Fetal Fraction Of Cell-free DNA Research Articles

Association between fetal fraction of cell-free DNA and adverse pregnancy outcomes.

To determine the association between fetal fraction (FF) levels in cell-free fetal DNA (cffDNA) testing and adverse pregnancy outcomes. This retrospective cohort study, conducted at a single center, involved 2063 pregnant women with normal 1st and 2nd trimester non-invasive prenatal test (NIPT) results between 2016 and 2021. Pregnancy outcomes were examined by determining the < 4% and < 5th percentile (3.6%) cut-off values for low fetal fraction (LFF). Pregnancy outcomes were also examined by dividing the FF into population-based quartiles. Adverse pregnancy outcomes were pregnancy-induced hypertensive diseases (PIHD), gestational diabetes mellitus (GDM), spontaneous preterm birth (PTB), intrahepatic cholestasis of pregnancy (ICP), small for gestational age (SGA), large for gestational age (LGA), low birth weight (LBW), macrosomia, and 1st and 5th minutes low APGAR scores (< 7). PIHD was significantly higher in LFF (< 4% and < 5th percentile) cases (p = 0.015 and p < 0.001, respectively). However, in population-based quartiles of FF, PIHD did not differ significantly between groups. Composite adverse maternal outcomes were significantly higher in the FF < 4% group (p = 0.042). When analyzes were adjusted for maternal age, BMI, and gestational age at NIPT, significance was maintained at < 4%, < 5th percentile LFF for PIHD, and < 4% LFF for composite adverse maternal outcomes. However, there was no significant relationship between LFF with GDM, ICP and PTB. Additionally, there was no significant association between low APGAR scores, SGA, LGA, LBW, macrosomia, and LFF concerning neonatal outcomes. Our study showed that LFF in pregnant women with normal NIPT results may be a predictor of subsequent PIHD.

A statistical investigation of parameters associated with low cell-free fetal DNA fraction in maternal plasma for noninvasive prenatal testing

Background Noninvasive prenatal testing (NIPT) is the most common method for prenatal aneuploidy screening. Low fetal fraction (LFF) is the primary reason for NIPT failure. Consequently, factors associated with LFF should be elucidated for optimal clinical implementation of NIPT. Methods In this study, NIPT data from January 2019 to December 2022 from the laboratory records and obstetrical and neonatal data from the electronic medical records were collected and analyzed. Subjects with FF >3.50% were assigned to the control group, subjects with FF <3.50% once were assigned to the LFF group, and subjects with FF <3.50% twice were assigned to the repetitive low fetal fraction (RLFF) group. Factors, including body mass index (BMI), gestational age, maternal age, twin pregnancy, and in vitro fertilization (IVF) known to be associated with LFF were assessed by Kruskal–Wallis H test and logistic regression. Clinical data on first trimester pregnancy-associated plasma protein-A (PAPP-A), beta-human chorionic gonadotropin (β-hCG), gestational age at delivery, birth weight at delivery, and maternal diseases were obtained from the hospital’s prenatal and neonatal screening systems (twin pregnancy was not included in the data on gestational age at delivery and the control group did not include data on maternal diseases.), and were analyzed using Kruskal–Wallis H test and Chi-square test. Results Among the total of 63,883 subjects, 63,605 subjects were assigned to the control group, 197 subjects were assigned to the LFF group, and 81 subjects were assigned to the RLFF group. The median of BMI in the three groups was 22.43 kg/m2 (control), 25.71 kg/m2 (LFF), and 24.54 kg/m2 (RLFF). The median gestational age in the three groups was 130 days (control), 126 days (LFF), and 122/133 days (RLFF). The median maternal age in the three groups was 29 (control), 29 (LFF), and 33-years-old (RLFF). The proportion of twin pregnancies in the three groups was 3.3% (control), 10.7% (LFF), and 11.7% (RLFF). The proportion of IVF in the three groups was 4.7% (control), 11.7% (LFF), and 21.3% (RLFF). The factors significantly associated with LFF included BMI [2.18, (1.94, 2.45), p < 0.0001], gestational age [0.76, (0.67, 0.87), p < 0.0001], twin pregnancy [1.62, (1.02, 2.52), p = 0.0353], and IVF [2.68, (1.82, 3.86), p < 0.0001]. The factors associated with RLFF included maternal age [1.54, (1.17, 2.05), p = 0.0023] and IVF [2.55, (1.19, 5.54), p = 0.016]. Multiples of the median (MOM) value of β-hCG and pregnant persons’ gestational age at delivery were significantly decreased in the LFF and RLFF groups compared to the control group. Conclusion According to our findings based on the OR value, factors associated strongly with LFF include a high BMI and the use of IVF. Factors associated less strongly with LFF include early gestational age and twin pregnancy, while advanced maternal age and IVF were independent risk factors for a second LFF result.

Fetal fraction of cell-free DNA in non-invasive prenatal testing and adverse pregnancy outcomes: a nationwide retrospective cohort study of 56,110 pregnant women

BackgroundNon-invasive prenatal testing by cell-free DNA analysis is offered to pregnant women worldwide to screen for fetal aneuploidies. In non-invasive prenatal testing, the fetal fraction of cell-free DNA in the maternal circulation is measured as a quality control parameter. Since fetal cell-free DNA originates from the placenta, the fetal fraction might also reflect placental health and maternal pregnancy adaptation. ObjectiveTo assess the association between the fetal fraction and adverse pregnancy outcomes. Study DesignWe performed a retrospective cohort study of women with singleton pregnancies opting for non-invasive prenatal testing between June 2018 and June 2019 within the Dutch nationwide implementation study (TRIDENT-2). Multivariable logistic regression analysis was used to assess associations between fetal fraction and adverse pregnancy outcomes. Fetal fraction was assessed as a continuous variable and as <10th percentile, corresponding to a fetal fraction below 2.5%. ResultsThe cohort comprised 56,110 pregnancies. In the analysis of fetal fraction as a continuous variable, a decrease in fetal fraction was associated with an increased risk of hypertensive disorders of pregnancy (adjusted OR [aOR] 2.27 [95% CI 1.89 to 2.78]), small for gestational age neonates <p10 (aOR 1.37 [1.28 to 1.45]) and <p2.3 (aOR 2.63 [1.96 to 3.57]), and spontaneous preterm birth from 24 to 37 weeks of gestation (aOR 1.02 [1.01 to 1.03]). No association was found for fetal congenital anomalies (aOR 1.02 [1.00 to 1.04]), stillbirth (aOR 1.02 [0.96 to 1.08]), or neonatal death (aOR 1.02 [0.96 to 1.08]). Similar associations were found for adverse pregnancy outcomes when fetal fraction was <10th percentile. ConclusionsIn early pregnancy, a low fetal fraction is associated with an increased risk of adverse pregnancy outcomes. These findings can be utilized to expand the potential of non-invasive prenatal testing in the future, enabling the prediction of pregnancy complications and facilitating tailored pregnancy management through intensified monitoring or preventive measures.

Association between the first and second trimester cell free DNA fetal fraction and spontaneous preterm birth

ABSTRACT Objective To evaluate whether the fetal fraction of cell-free DNA at the first and second trimesters is associated with spontaneous preterm birth. Methods This was a retrospective cohort study with singleton pregnancies who underwent noninvasive prenatal testing. According to pregnancy outcome, eligible patients were divided into a delivery group ≥37 weeks of pregnancy (term group) and <37 weeks of pregnancy (spontaneous preterm group). Stepwise linear regression was used to identify maternal characteristics associated with the fetal fraction of cell‐free DNA. Logistic regression analysis was performed to evaluate the association between the fetal fraction of cell-free DNA and spontaneous preterm birth, adjusted for confounding factors. Results 14,020 cases were included in the study, 13292 cases (94.81%) in the term group and 728 cases (5.19%) in the spontaneous preterm group. The cell-free fraction of fetal DNA was inversely correlated with maternal age and body mass index. Positively correlated with gestational age, fertility, and assisted reproductive technology. After adjusting for the covariates, logistic regression analysis revealed no statistically significant association between the fetal fraction of cell-free DNA and spontaneous preterm birth. Conclusion In our original study, we found no association between the fetal fraction on NIPT and subsequent spontaneous preterm birth.

Correlation of low fetal fraction of cell-free DNA at the early second-trimester and pregnancy complications related to placental dysfunction in twin pregnancy.

This study aimed to determine the correlation between fetal fraction (FF) of cell-free DNA (cf-DNA) and pregnancy complications related to placental dysfunction in Twin Pregnancy. This retrospective cohort study analyzed twin pregnant women who underwent non-invasive prenatal testing (NIPT) at 12+0-26+6 weeks of gestation from April 2017 to April 2021. Low fetal fraction (LFF) was defined individually as less than the 25th, 10th, 5th, and 2.5th percentile among all fetal fractions in the cohort. Primary outcomes included gestational hypertension (GH), preeclampsia (PE), gestational diabetes mellitus (GDM), and small for gestational age (SGA). Logistic regression analysis was used to assess the relationship between LFF and pregnancy complications. A total of 500 twin pregnancies (male-male twins, 245; female-female twins, 255) were included in this study. In LFF group (FF < 25th percentiles), maternal BMI was significantly higher than FF > 75th percentiles (23.6 kg/m2 vs. 21.3 kg/m2; P < 0.001). The risk of SGA increased gradually from FF < 25th percentiles [adjusted odds ratio (OR), 1.71; 95% confidence interval (CI), 1.07-2.99; P = 0.016] to FF < 2.5th percentiles (adjusted OR, 4.44; 95% CI,1.33-14.82; P < 0.015). In addition, the risks of SGA in both fetuses were higher than the risks of at least one fetus SGA in LFF group. LFF had no correlation with GH, PE, and GDM in twin pregnancy. LFF has a strong association with increased risk of SGA in twin pregnancy. Moreover, FF of cf-DNA may provide a new idea for the early screening of diseases related to placental dysfunction in twin pregnancy.

The effect of abnormal placentation on maternal serum fetal fraction of cell-free DNA.

Abnormal placentation may affect the maternal serum fraction of cell-free fetal DNA (fetal fraction) determined as part of non-invasive prenatal screening (NIPS). This study aimed to assess whether the fetal fraction can predict placenta accreta spectrum (PAS) with or without placenta previa (PP). We also investigated the impact of trophoblastic invasion depth on the fetal fraction. This is a retrospective case-control study of pregnant women with and without abnormal placentation carrying a singleton and having undergone NIPS prior to 20weeks of gestation. The eligible subjects were selected from a cohort managed at our institution for PAS suspected antenatally. We compared women with normal placentation (controls) to PAS, PP, or PAS+PP cases. Data were abstracted from electronic medical records, and PAS was confirmed histologically. Of the 146 patients in our cohort, 8 controls, 10 PP, 6 PAS, and 7 PAS+PP cases were eligible for the study. Among the groups, there were no significant differences in baseline demographic and clinical characteristics except the median number of prior uterine surgeries. Also, the groups did not significantly differ in their median fetal fraction. The fetal fraction did not discriminate any group when stratified according to the depth of placental invasion, i.e.,no PAS, abnormally adherent, and abnormally invasive placenta. The maternal serum fraction of cell-free fetal DNA measured before 20weeks of gestation is not predictive of PAS with or without concurrent PP or the depth of trophoblastic invasion.

Low Fetal Fraction of Cell Free DNA at Non-Invasive Prenatal Screening Increases the Subsequent Risk of Preterm Birth in Uncomplicated Singleton Pregnancy.

ObjectiveTo examine the association between low fetal fraction (FF) of cell free DNA determined at non-invasive prenatal screening (NIPS) and the subsequent risk of preterm birth in uncomplicated singleton pregnancy.MethodsWe retrospectively interrogated NIPS System and hospitalization records from April 2018 to August 2019 and obtained results from 1521 consecutive and uncomplicated women with singleton pregnancy in which plasma FF of cell free DNA at NIPS had been investigated together with birth outcomes. We examined the association between FF and preterm birth (PTB) by regression analysis.ResultsThe incidence of preterm birth, low birthweight, and macrosomia in the study population was 5.06%, 2.89%, and 7.17%, respectively. FF at NIPS in the second to fourth quartiles (8.40–11.07, 11.08–13.70, and >13.70%, respectively) was associated with higher gestational age at delivery relative to the lowest quartile (<8.40%), with estimated mean increases of 0.27 weeks (95% CI: 0.05–0.49), 0.29 weeks (95% CI: 0.06–0.51), and 0.28 weeks (95% CI: 0.05–0.51), respectively (P for trend = 0.027). Low FF (< the 5th percentile) was associated with an increased risk of PTB (adjusted OR: 2.23, 95% CI: 1.01–4.98, P = 0.047) compared to normal FF (≥ the 5th and ≤ the 95th percentiles). In addition, when compared to women with normal FF and body mass index (BMI) <25 at NIPS, the risk of early PTB (< 34 weeks gestation) was remarkably significantly higher among those with low FF and BMI ≥25 (adjusted OR: 6.29, 95% CI: 1.71–23.15, P = 0.006).ConclusionOur study supports the association of low FF at NIPS with PTB (especially early PTB) for uncomplicated singleton pregnancy.

Simulated confined placental mosaicism proportion (SCPMP) based on cell-free fetal DNA fraction enrichment can reducefalse-positive results in non-invasive prenatal testing.

To decrease the false-positive rate of NIPT using cell-free fetal DNA (cffDNA) fraction enrichment and the simulated confined placental mosaicism proportion (SCPMP) threshold application via cffDNA quantification. Using a cffDNA enrichment method, 303 plasma samples with positive NIPT results (Z-score > 3.0; 200 true-positive and 103 false-positive cases) were re-sequenced. A method to calculate the SCPMP based on the quantified cffDNA fraction was developed; the SCPMP threshold between true- and false-positive NIPT results was determined and used for re-analyses. With enrichment, the fetal fraction of the 303 samples was 26.9±8.4%, compared to 11.0±3.2% without enrichment. The optimized threshold method with double determination using the Z-value-defined SCPMP can reduce the false-positive rates for trisomies 21, 18, and 13 by 87%, 80%, and 88.9%, respectively. Our optimized method can decrease the false-positive rate of NIPT results.

Comparison of the Fetal Fraction of Cell-Free DNA in In-Vitro Fertilization (IVF) Versus Natural Conception Evaluation of the Fetal Fraction With IVF Parameters.

BackgroundAs the offspring of assisted reproduction techniques (ARTs) have become a substantial proportion of the population, increased attention has been placed on the safety of ART. Investigators have focused on identifying a tool that combines molecular or biological tests that can predict the outcomes of in-vitro fertilization (IVF) or intracytoplasmic sperm injection and the resulting pregnancy after ART-mediated embryo implantation. This study aimed to answer the following questions: is there a difference between natural conception and IVF pregnancies regarding fetal fraction (FF) of cell-free DNA (cfDNA) in maternal age, birth weight, gender, and gestational age? Is there a difference between FF concentration regarding the parameters of IVF as possible predictive factors affecting the outcomes of IVF?MethodologyThis study included 31 women with singleton pregnancies conceived via IVF who underwent cell-free fetal DNA (cffDNA) screening for trisomy 13, 18, and 21; sex determination; and FF. The control group included 55 women who experienced natural conception. For all women, anthropometric characteristics such as age, weight, height, and body mass index (BMI) were recorded. For the IVF group, early follicular phase values of follicle-stimulating hormone, luteinizing hormone, prolactin, anti-müllerian hormone, thyroid-stimulating hormone, and estradiol were recorded.ResultsThe natural conception and IVF groups were similar regarding maternal age, BMI of the mother, gender, birth weight, and gestational age. FF was not significantly different between the natural conception and IVF groups (10 (3.8) vs. 9 (2.6); p = 0.144). The results were similar after adjusting for maternal age via regression analysis. cfDNA was not associated with maternal age, birth weight, gender, or gestational age in the entire study sample or separately for the natural conception and IVF groups. No significant correlation was found between cfDNA and IVF parameters.ConclusionsThe FF is an important factor for non-invasive prenatal testing (NIPT) accuracy. Several studies have found a reduction in FF in pregnancies following ART compared with natural conception, while other studies have presented no differences in the FF. All researchers agree on the importance of NIPT; however, knowledge on how the FF is affected in ART pregnancies compared with naturally conceived pregnancies is very limited. In this study, no difference in FF for the IVF group compared with natural conception women was observed. The cffDNA concentrations in maternal serum do not appear to be affected in IVF conception. We suggest that FF is an independent factor compared with IVF parameters.

Noninvasive prenatal testing of hereditary colorectal cancer syndromes using cell-free DNA in maternal plasma.

This study aimed to establish a practical protocol for early noninvasive prenatal testing (NIPT) for fetuses at risk of Peutz-Jeghers syndrome or familial adenomatous polyposis, two classical types of hereditary colorectal cancer syndromes, for risk evaluation and whole-life monitoring. Target enrichment was performed using hybridization probes coordinating the serine-threonine kinase 11 gene region and APC gene region, with 1458 highly heterozygous Single Nucleotide Polymorphisms included. Semitarget amplification random sequencing was used for large fragment deletion detection. For relative haplotype dosage (RHDO) analysis, haplotype construction was performed by segmented haplotype estimation and imputation tool software, the circular binary segmentation algorithm was used for recombination event calculation, and Bayes factor was used for the determination of whether the fetus was affected. Haplotypes were successfully constructed in the nine recruited families with different pedigree characteristics, and the results for the RHDO analysis were consistent with the amniocentesis sampling detection results. The cell-free fetal DNA fraction can be detected as low as 2% in maternal plasma. This is the first NIPT assay on hereditary colorectal cancer syndromes based upon RHDO analysis.

The value of re-sampling for patients who had failed non-invasive prenatal testing due to low cell-free fetal DNA fraction

To assess the value of re-sampling for patients who had failed non-invasive prenatal testing (NIPT) due to low cell-free fetal DNA (cffDNA) fraction. Clinical data of 20 387 patients undergoing NIPT test was reviewed. The patients were re-sampled when initial blood test did not yield a result due to cffDNA fraction. The results were analyzed, and the outcome of pregnancy was followed up. Among all samples, 17 (0.08%) had failed to yield a result due to low cffDNA fraction, all of which accepted re-sampling. A result was attained in 16 cases, with a success rate of 94.12%. Only one sample had failed the re-test. For patients who had failed the initial NIPT due to low cffDNA fraction, re-sampling should be considered with gestational week and ultrasound results taken into consideration.

Estimation of cell-free fetal DNA fraction from maternal plasma based on linkage disequilibrium information

Cell-free fetal DNA fraction (FF) in maternal plasma is a key parameter affecting the performance of noninvasive prenatal testing (NIPT). Accurate quantitation of FF plays a pivotal role in these tests. However, there are few methods that could determine FF with high accuracy using shallow‐depth whole‐genome sequencing data. In this study, we hypothesized that the actual FF in maternal plasma should be proportional to the discrepancy rate between the observed genotypes and inferred genotypes based on the linkage disequilibrium rule in certain polymorphism sites. Based on this hypothesis, we developed a method named Linkage Disequilibrium information-based cell-free Fetal DNA Fraction (LDFF) to accurately quantify FF in maternal plasma. This method achieves a high performance and outperforms existing methods in the fetal DNA fraction estimation. As LDFF is a gender-independent method and developed on shallow-depth samples, it can be easily incorporated into routine NIPT test and may enhance the current NIPT performance.

Screening for Fetal Aneuploidy and Sex Chromosomal Anomalies in a Pregnant Woman With Mosaicism for Turner Syndrome-Applications and Advantages of Cell-Based NIPT.

Background: Cell-free NIPT and cell-based NIPT are risk-free testing options using maternal blood samples to screen for fetal aneuploidies, but the methods differ. For cell-free NIPT, the fetal fraction of cell-free DNA in plasma is analyzed with a high background of maternal DNA. In contrast, for cell-based NIPT, a limited number of the rare, intact fetal cells are isolated for the genetic analysis. This case demonstrates the differences regarding testing for fetal sex-chromosomes anomalies (SCAs) between these two tests.Materials and Methods: A pregnant woman with mosaicism for Turner syndrome opted for NIPT in first trimester. For the cell-free NIPT analysis, DNA extraction, genome-wide massive parallel sequencing, and data analysis were carried out as described by the kit manufacturer (Illumina©, San Diego, CA, USA). For cell-based NIPT, the first sample gave no result, but the woman consented to repeat cell-based NIPT. After whole genome amplification and STR analysis, fetal DNA from three individual fetal cells was subjected to chromosomal microarray (aCGH, Agilent oligoarray, 180 kb).Results: Fetal fraction was 7%, and cell-free NIPT showed 2 copies of chromosomes 13, 18, and 21 and a decreased proportion of chromosome X, suggestive of fetal Turner syndrome. In contrast, the cell-based NIPT result showed no aneuploidy and two X-chromosomes in the fetus.Conclusion: cell-based NIPT may provide a non-invasive testing option to screen for SCAs in women with mosaicism for monosomy-X in blood, where cell-free NIPT cannot discriminate whether the X-loss is maternal or fetal.

The impact of maternal autoimmune disease on cell-free DNA test characteristics

Maternal biologic factors can affect the fetal fraction in cell-free DNA-based prenatal screening assays, thereby limiting the effectiveness. Higher rates of indeterminate results because of a low fetal fraction have been described in cases of maternal autoimmune disease in pregnancy. Existing studies are confounded by the concomitant maternal use of anticoagulants, which may independently influence the test characteristics. This study aimed to evaluate the differences in fetal fraction, indeterminate results, and total cell-free DNA concentration among women with an autoimmune disease in comparison with controls, using our in-house developed, noninvasive prenatal screening platform in the absence of maternal anticoagulation use. This was a retrospective, single institution cohort study of a previously validated, cell-free DNA-based, noninvasive prenatal screening assay using a low-pass whole-genome sequencing platform between 2017 and 2019. A diagnosis of an autoimmune disease included systemic lupus erythematosus, rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, and others. Immunomodulator therapies included biologics, corticosteroids, hydroxychloroquine, azathioprine, and intravenous immunoglobulin. Women who were using anticoagulants were excluded. We evaluated the association between autoimmune disease and fetal cell-free DNA fraction, indeterminate results, and total cell-free DNA concentration using univariate and multivariate analyses, stratified according to immunomodulator therapy and adjusted for body mass index, fetal sex, and gestational age at sample collection. A total of 1445 patients met inclusion criteria. Of those, 43 women had a confirmed autoimmune disease, with 25 of those not on immunomodulator therapy and 18 on immunomodulator therapy. The mean fetal fraction for women with an autoimmune disease was significantly lower than for controls (9.7% vs 11.9%; P=.004). The rate of indeterminate results was significantly higher among women with an autoimmune disease than among controls (16.3% vs 3.5%; P<.001). The total cell-free DNA concentration was not statistically different between the groups (94.8 pg/µL for women with an autoimmune disease vs 83.9 pg/µL for controls; P=.06). In a logistic regression, women with an autoimmune disease had significantly higher odds of receiving an indeterminate result than controls, (adjusted odds ratio, 5.3; 95% confidence interval, 2.0-14.2). Linear regression analysis showed a significant negative association between having an autoimmune disease and the fetal cell-free DNA fraction (aβ, -2.1; 95% confidence interval, -3.4 to -0.6). When stratifying by treatment status, the mean fetal fraction was 9.8%, 9.6%, and 11.9% for women with an autoimmune disease not on immunomodulator therapy, women with an autoimmune disease on immunomodulator therapy, and the controls, respectively (P=.02). The rate of indeterminate results increased in a stepwise fashion from 3.5% to 11.1% to 20.0% for controls, women with an autoimmune disease on immunomodulator therapy, and women with an autoimmune disease not on immunomodulator therapy, respectively (P<.001). Logistic regression analysis demonstrated higher odds of an indeterminate resultfor women with an autoimmune disease not on immunomodulator therapy than for controls, (adjusted odds ratio, 7.3; 95% confidence interval, 2.3-22.5). There was a negative association between women with an autoimmune disease not on immunomodulator therapy and the fetal fraction when compared with controls (aβ, -2.2; 95% confidence interval, -4.2 to -0.3). Women with an autoimmune disease have lower fetal cell-free DNA fractions and higher rates of indeterminate results than women without an autoimmune disease. There was no difference in total cell-free DNA concentration. Treatment of maternal autoimmune diseases with immunomodulator therapy may decrease the indeterminate result rate.

Discordant structural chromosomal aberrations in chorionic villi and amniotic fluid leading to a formation of an isochromosome 21: a case report

BackgroundFetoplacental discrepancies occur in approximately 1–2% of analyzed prenatal cases. They are typically due to confined placental mosaicism, where an aberration is observed in the placental cells but not found in the fetal cells. Confined placental mosaicism usually involves aneuploidies and more sparsely structural chromosomal aberrations. To the best of our knowledge, this is the first reported case of a discrepancy in the analyses of chorionic villus sampling and amniocentesis involving two different structural chromosomal aberrations of chromosome 21.Case presentationWe report a 33-year-old woman who was referred for a non-invasive prenatal testing due to an increased risk of trisomy 21 gleaned from a combined ultrasound and blood test. The non-invasive prenatal testing showed an increased risk of trisomy 21 with a normalized coverage signal that did not match the fetal cell-free DNA fraction. Rapid aneuploidy detection performed on uncultured chorionic villi indicated mosaicism for trisomy 21. The follow-up analyses revealed discordant chromosomal aberrations: 46,XY,der(21)t(10;21)(p11.21;q10) in the analysis of the chorionic villus sampling and 46,XY, + 21,der(21;21)(q10;q10) in the analysis of the amniocentesis. Thus, the analyses indicated mosaicism for a cell line containing trisomy 21 and a cell line containing a partially duplicated short arm of chromosome 10 in the chorionic villi and complete trisomy 21 resulting from an isochromosome 21 in the amniotic fluid. The analyses of the lymphocytes and the fibroblasts of the woman were normal.ConclusionsWe propose a multiple-step mechanism as a possible theoretical explanation for the formation of these discordant structural chromosomal aberrations in the chorionic villi and amniotic fluid. With this case report, we want to highlight the importance of understanding the possible underlying embryological mechanisms when interpreting results from different prenatal analyses.

Sequencing Cell-free Fetal DNA in Pregnant Women With GCK-MODY.

Individuals with monogenic diabetes due to inactivating glucokinase (GCK) variants typically do not require treatment, except potentially during pregnancy. In pregnancy, fetal GCK genotype determines whether treatment is indicated, but noninvasive methods are not clinically available. This work aims to develop a method to determine fetal GCK genotype noninvasively using maternal cell-free fetal DNA. This was a proof-of-concept study involving 3 pregnant women with a causal GCK variant that used information from 1) massive parallel sequencing of maternal plasma cell-free DNA, 2) direct haplotype sequences of maternal genomic DNA, and 3) the paternal genotypes to estimate relative haplotype dosage of the pathogenic variant-linked haplotype. Statistical testing of variant inheritance was performed using a sequential probability ratio test (SPRT). In each of the 3 cases, plasma cell-free DNA was extracted once between gestational weeks 24 and 36. The fetal fraction of cell-free DNA ranged from 21.8% to 23.0%. Paternal homozygous alleles that were identical to the maternal GCK variant-linked allele were not overrepresented in the cell-free DNA. Paternal homozygous alleles that were identical to the maternal wild-type-linked allele were significantly overrepresented. Based on the SPRT, we predicted that all 3 cases did not inherit the GCK variant. Postnatal infant genotyping confirmed our prediction in each case. We have successfully implemented a noninvasive method to predict fetal GCK genotype using cell-free DNA in 3 pregnant women carrying an inactivating GCK variant. This method could guide tailoring of hyperglycemia treatment in pregnancies of women with GCK monogenic diabetes.

Obesity and no call results: optimal timing of cell-free DNA testing and redraw

Fetal fraction of cell-free DNA decreases with increasing maternal weight. Consequently, cell-free DNA screening for fetal aneuploidy has higher screen failures or "no call" rates in women with obesity owing to a low fetal fraction. The optimal timing of testing based on maternal weight is unknown. This study aimed to identify the optimal timing of initial cell-free DNA testing based on maternal weight and to identify the optimal timing of repeat cell-free DNA testing in cases with an initial screen failure. This was a retrospective cohort study of women undergoing cell-free DNA for fetal aneuploidy screening between 9 and 18 weeks through a single laboratory over 1 year from 2018 to 2019. Fetal fraction change per week was calculated, and generalized linear models were used to calculate relative risk and 95% confidence interval of a no call result at given maternal weights and gestational ages. The vast majority of samples (99.22%) received a test result. The risk of a no call result owing to a low fetal fraction was higher with increasing maternal weight. At 9 to 12 weeks, the rate of a no call result owing to a low fetal fraction in women who weighed <150 lb was 0.14% compared with 17.39% in women weighing >400 lb. Fetal fraction increased with increasing gestational age, although the incremental increase in fetal fraction over time is inversely proportional to maternal weight. At 13 to 18 weeks' gestation, 6.45% of women weighing >400 lb received a no call result owing to a low fetal fraction. In women in the highest weight category, >400 lb, fetal fraction increased 0.5% with each week of gestation. Although the risk of a no call result increases with maternal weight, cell-free DNA screening should be offered to all women at 9 to 12 weeks' gestation, allowing the option to have chorionic villus sampling after a positive test result. Pretest counseling for women with obesity should include the increased chance for a test failure. Most women weighing less than 400 lb will receive a test result and more than 80% of women with a weight of >400 lb will receive a test result at 9 to 12 weeks' gestation. Data regarding the expected increase in cell-free DNA fetal fraction per week may help guide the timing of a redraw to optimize test success.

1053 Abnormal placentation and affect on fetal fraction of cell-free DNA

Abnormal placentation may affect fetal fraction (FF) of cell-free fetal DNA (cffDNA). Second-trimester cffDNA fraction is higher in pregnancies complicated by placenta previa (PP) alone, but not with placenta accreta spectrum (PAS) compared to women with normal placentation. Since concurrent PP and PAS occurs frequently, we hypothesized a decrease in the FF due to PAS might be masked in patients with concurrent placenta previa. We compared women with normal placentation to cases of PAS, PP, or PAS+PP, all of whom had non-invasive prenatal screening (NIPS). Assuming a standard deviation of 3% for the population and using an α of .05 and β of .8, we estimated that we need at least six subjects in each group to detect a difference of 6% in means of cffDNA fraction. Data was abstracted from electronic medical records. PAS spectrum disorders were confirmed histologically and/or clinically. We used the Shapiro-Francia test to assess the distribution of our data for normality. Normally distributed data were compared with unpaired t-test. Data with non-normal distribution were compared with the Mann-Whitney test. Percentages were compared with Fisher's exact test. We studied 10 cases of normal placentation, 9 cases of PAS, 8 cases of PAS+PP, and 6 cases with PP. There were no significant differences between the groups, including maternal age, ethnicity, pre-pregnancy body mass index, previous cesarean deliveries, pregnancy-induced hypertension, autoimmune disease, treatment with anti-coagulants, median gestational age when blood sample was collected, or commercial laboratory where NIPS was performed. The mean FF of cffDNA from patients with PAS was significantly lower than those with normal placentation or with PAS+PP, i.e., 95% confidence interval for the difference between means, .3 to 6.9% and .3 to 7.8, respectively (p< .05). The difference between PP and other groups were not statistically significant. The pathogenesis leading to PAS is associated with low fetal fraction of cffDNA in the maternal serum. This association is masked among those with concurrent PAS and PP.

Fetal fraction of cell-free DNA in pregnancies after fresh or frozen embryo transfer following assisted reproductive technologies.

Is the fetal fraction (FF) of circulating cell-free DNA (cfDNA) affected in pregnancies following ART treatment with either fresh or frozen embryo transfer (ET) compared with natural conception? This study shows a significant reduction in the FF in ART patients compared with naturally conceived pregnancies, which seems to be more pronounced after fresh ET compared with frozen ET. Non-invasive prenatal testing (NIPT) is based on cfDNA in maternal blood, of which about 10% is of placental origin and thus represents the fetal karyotype. Validation studies have demonstrated a high sensitivity, specificity and positive predictive value of NIPT for the detection of fetal trisomy 21, 18 and 13. Nevertheless, the FF of cfDNA is an important factor for NIPT test accuracy. Several studies have found a reduction in FF for pregnancies following ART in comparison with natural conception. However, knowledge on how the FF is affected in ART pregnancies after fresh ET compared with frozen ET is very limited. The study was designed as a case-control study. A total of 54 women with an ongoing pregnancy following ART treatment were included. After exclusion for different reasons, statistical analyses were based on 23 NIPT samples from pregnant women treated with fresh ET and 26 NIPT samples from pregnant women treated with frozen-thawed ET in a modified natural cycle. Women were included between February 2018 and November 2018. The results were compared with a control group of 238 naturally conceived pregnancies with a high-risk result from the combined first trimester screening (cFTS). The study included women from the Fertility Clinics at Copenhagen University Hospital Hvidovre and Copenhagen University Hospital Rigshospitalet. Blood samples for NIPT analysis were drawn between 11 + 0 and 14 + 2 weeks of gestation and were all analyzed at the NIPT Center at Copenhagen University Hospital Hvidovre. The NIPT-test was performed by massive-parallel whole-genome sequencing. The FF was determined using the SeqFF algorithm. We found a reduction in FF in ART patients compared with naturally conceived pregnancies, and the reduction was more pronounced for ART pregnancies after fresh ET (mean FF = 0.049) compared with frozen ET (mean FF = 0.063) (multivariate analysis adjusted for maternal BMI, P = 0.02). Another multivariate analysis, adjusted for BMI and multiples of median (MoM) values for pregnancy-associated plasma protein-A (PAPP-A), demonstrated a significantly reduced FF for ART pregnancies (mean FF = 0.056) compared with naturally conceived pregnancies (mean FF = 0.072) (P < 0.0001). We found that FF was significantly reduced with increasing maternal BMI (P < 0.0001) and with decreasing MoM values of PAPP-A (P = 0.003). A limitation of our study design was the relatively small sample size. Another limitation was that the control group was not matched with the ART-treated women. The majority of the women from the control group had a high risk from cFTS, thereby their biochemical markers were diverging. However, the biochemical markers for the ART-treated women with fresh or frozen ET were not divergent within the subgroups. Concurrent with other studies demonstrating a reduced FF for singleton pregnancies after ART treatment compared with naturally conceived pregnancies, we found a reduction in FF between the two groups. This is one of the first studies to examine FF in ART pregnancies after fresh ET compared with frozen ET, hence the existing knowledge is limited. We find that FF is even more reduced in pregnancies following fresh ET compared with frozen ET, which might possibly reflect the predisposition of being small for gestational age after fresh ET compared with natural cycle frozen ET. The study was supported by the A.P. Møller og Hustru Chastine Mc-Kinney Møllers Fond til almene Formaal (the A.P. Møller Foundation for General Purposes). All authors declare no conflicts of interest. NA.

Association between fetal fraction at the second trimester and subsequent spontaneous preterm birth.

To evaluate the association between the fetal fraction of cell-free DNA at the second trimester and subsequent spontaneous preterm birth. In this retrospective cohort study, data were collected from women with singleton pregnancies who underwent noninvasive prenatal testing at 14 to 25weeks of gestation. The eligible patients were classified into three groups according to pregnancy outcome: birth at ≥37weeks of gestation (term group), delivery at <34weeks of gestation (early spontaneous preterm), and delivery at 34+0 to 36+6 weeks of gestation (late spontaneous preterm). Stepwise linear regression was performed to determine the maternal characteristics associated with the fetal fraction of cell-free DNA. Logistic regression was used to determine the relationship between the fetal fraction of cell-free DNA and pregnancy outcomes by adjusting for history of preterm birth. A total of 8129 singleton pregnancies met the recruitment criteria. Among them, 7790 (95.83%) were in the term group, 284 (3.49%) were in the late spontaneous preterm group, and 55 (0.68%) were in the early spontaneous preterm group. The fetal fraction of cell-free DNA was negatively correlated with body mass index, maternal age, nulliparity, and history of spontaneous preterm birth; positively correlated with gestational age; and not correlated with assisted reproduction or surface antigen of hepatitis B virus (HBsAg) positivity. After adjusting for history of preterm birth, a logistic regression analysis demonstrated no statistically significant associations between the fetal fraction of cell-free DNA and spontaneous preterm birth in any of the preterm groups (<34weeks, 34+0 to 36+6 weeks, and <37weeks). Our preliminary study found no relationship between the fetal fraction on NIPT at the second trimester and subsequent spontaneous preterm birth.