Partial gene duplications (PGDups) are a significant contributor to genetic disease. The precise genomic location and structure of PGDups are often unresolved using conventional methods, so prenatal diagnosis for PGDups is challenging, especially without ultrasound abnormalities. We retrospectively applied structural variation sequencing (SVseq) to 26 amniotic fluid samples with PGDups initially identified by chromosomal microarray or sequencing. SVseq utilized mate-pair library construction and high-throughput sequencing to map PGDup structures. Pathogenicity was classified using ACMG guidelines, followed by postnatal phenotypic follow-up. SVseq deciphered the PGDup structure for all twenty-six cases. Twenty-two (84.62%) were tandem duplications (TDs), three (11.54%) chromosomal complex rearrangements (CCRs), and one (3.85%) had no duplication. Among twenty-two TDs, thirteen were extragenic (TDEG), preserving gene integrity, and were classified as benign or variants of uncertain significance (VUS). Nine were intragenic (TDIG), disrupting gene structure, and were rated pathogenic or likely pathogenic (P/LP) or VUS. Postnatal follow-up revealed obvious abnormal phenotypes in only two TDIG cases (one inherited and one de novo). SVseq effectively resolves PGDup location and structure, allowing confident pathogenicity assessment and clear genotype-phenotype correlation. SVseq is a robust method for prenatal PGDup evaluation that could be adopted in diagnostic protocols to improve clinical outcomes.

Prenatal genetic testing for imprinting disorders is rarely requested with the exception of Beckwith-Wiedemann syndrome (BWS) which is associated with specific ultrasound findings (e.g.,placental mesenchymal dysplasia, omphalocele). However, genetic testing for BWS is challenging as aberrant DNA methylation has to be addressed which often occur as mosaicism. As a growing number of requests for prenatal BWS testing is observed, data from genetic prenatal BWS testing was compiled to delineate its suitability as well as limitations. Three European laboratories compiled the experiences from 646 prenatal samples. The samples were analysed by methylation-specific assays targeting the imprinting centres in 11p15.5, in a sub-cohort CDKN1C was sequenced. The overall detection rate for BWS specific molecular disturbances was 9.75%, and the spectrum of alterations reflected that from postnatal BWS cohorts. The rate of failing samples was in total 4.3%, nearly all failures were observed in native samples. Prenatal testing for BWS should be considered in pregnancies with ultrasound findings or family history suggestive for BWS. In the majority of tests, evaluable results can be achieved, though mosaicism can never be excluded and therefore false-negative results are possible.

To evaluate whether fetal cerebrovascular resistance estimated by middle cerebral artery pulsatility index (MCA PI) and cerebroplacental ratio (CPR) predicts 2-year neurodevelopment, accounting for physiology-based subtypes of congenital heart disease (CHD). This cohort study included fetuses with isolated CHD and healthy controls. Cardiac physiology was classified by ventricular circulation, outflow obstruction and expected cerebral substrate concentration. All subjects underwent fetal echocardiography and neurodevelopmental evaluation at 2years of age using the Bayley Scales of Infant and Toddler Development. There were no differences in MCA PI or CPR between cases (n=74) and controls (n=45). There were no associations between cerebral Dopplers and neurodevelopment in CHD overall. When stratified by fetal cardiac physiology, lower MCA PI was associated with higher Bayley cognitive, language, and motor scores and lower CPR with higher Bayley cognitive and language scores in cases with systemic outflow tract obstruction. Lower CPR was associated with higher cognitive score in single ventricle circulation. In multivariable analysis of predictors of neurodevelopment in cases overall, lower fetal brain volume predicted lower cognitive score, lower maternal education predicted lower language score, and lower fetal brain volume and single ventricle circulation predicted lower motor score. Lower cerebrovascular resistance predicted improved neurodevelopmental outcomes only among cases with systemic outflow tract obstruction and/or single ventricle physiology, suggesting that effective compensatory cerebral autoregulation is CHD-type specific.

Severe brain injury has been reported following fetoscopic laser ablation (FLA) for twin-to-twin transfusion syndrome (TTTS), but imaging patterns and temporal evolution remain poorly defined. This study aimed to characterize the progression of severe brain injury after FLA. We conducted a retrospective case series of TTTS pregnancies with severe brain injury identified after FLA at the Ontario Fetal Center (June 2023-March 2025). FLA was performed for Quintero stage≥II and selected stage I cases. Severe abnormalities were defined as severe intraventricular haemorrhage or destructive lesions. Serial ultrasound and fetal MRI were reviewed and categorized as early (<4weeks) or late (≥4weeks) post-FLA. Fifteen fetuses from 14 pregnancies were identified. Mean gestational age at FLA was 19.7±3.2weeks; 66.7% were stage III-IV and 60% were donor twins. Early imaging (n=8) most commonly showed periventricular haemorrhagic infarction (62.5%) and cerebellar haemorrhage (25.0%). Late imaging (n=13) predominantly demonstrated cerebral volume loss (76.9%), often involving the parietal lobes, with polymicrogyria (38.5%) and Wallerian degeneration (30.8%). Findings remained unchanged after 4weeks. Brain injury after FLA evolves from acute haemorrhagic/ischaemic insults to irreversible destructive changes. These preliminary findings suggest a consistent pattern of injury that warrants further prospective study.

The aim of this study was to evaluate the feasibility and clinical value of implementing first-trimester molecular HPA screening to identify pregnancies at risk for FNAIT. In this prospective cohort study, pregnant women were genotyped during the first trimester for HPA-1, -2, -3, -4, -5, -6, -9, and -15 using molecular methods. When low-frequency maternal genotypes were identified, paternal genotyping and risk stratification were performed to assess maternal-fetal incompatibility. At-risk pregnancies underwent structured clinical monitoring, and neonatal platelet counts were obtained at birth. Among 200 screened pregnancies, three (1.5%) were HPA-1b/1b. Prenatal screening identified five pregnancies at risk for FNAIT: three involving HPA-1, one HPA-3, and one HPA-15 incompatibility. Two neonates required compatible platelet transfusions. Early detection allowed anticipatory perinatal management and facilitated timely transfusion support when indicated. First-trimester molecular HPA screening is feasible and enables an early identification of pregnancies at risk for FNAIT across multiple antigen systems, allowing for appropriate clinical interventions. These findings support the potential role of targeted prenatal screening programs in improving the recognition and management of FNAIT, even in populations with a low prevalence of HPA-1a-negative women.

Cell free DNA (cfDNA) screening for common aneuploidies is now widely integrated into prenatal care, and recent advances in next-generation sequencing, enhanced by unique molecular indexing methodology, have enabled cfDNA for selected single-gene disorders (cfDNA-SGD). Commercially available cfDNA-SGD panels target predominantly either de novo autosomal dominant or X-linked conditions that have recognizable prenatal or neonatal phenotypes. However, it remains a screening modality that relies on placental cell-free DNA, and encounters limitations. In this review, we summarize a currently available cfDNA-SGD panel that screens for 25 autosomal or X-linked dominant conditions corresponding to 30 unique genes, with several genes contributing to multiple conditions on the panel. We highlight the potentially associated prenatal and postnatal phenotypes and the imaging modalities that may help refine a prenatal genetic evaluation. We also discuss how ultrasound, fetal echocardiography, and fetal MRI across all trimesters can refine the prenatal differential diagnosis and help contextualize cfDNA-SGD results, while emphasizing that imaging findings remain the primary guide for management and that confirmatory diagnostic testing is required before clinical decisions and action.

To evaluate ethnic disparities in carrier status ascertainment between Tier 3 (conditions with carrier frequency ≥ 1/200) and Tier 4 panels (conditions with carrier frequencies < 1/200), and to assess the utility of Tier 4-only screening in an ethnically diverse cohort. This IRB-approved retrospective chart review included adults undergoing carrier screening panel between January 2020 and April 2024, with self-reported ethnicities mapped to regions based on the United Nations Geoscheme, a system to group countries into regions used for analysis. We calculated the prevalence and number needed to screen (NNS) for Tier 4-only variants across geographic regions and ancestral subgroups. Among 2000 patients, 65.7% carried at least one Tier 4-only variant across the cohort, with most ancestral subgroups showing ≥ 60% prevalence. NNS to detect one Tier 4-only carrier ranged from 1.0 to 2.2, with the greatest efficiency in Africa, Southeast Asia, and Eastern Europe. Carrier couples were identified across multiple regions, with NNS ranging from 7.3 to 58.1. Tier 3 panels rely on carrier frequency thresholds largely derived from European populations and fail to identify carriers in underrepresented ethnic groups. Tier 4 panels provide greater carrier ascertainment across diverse populations and yield lower NNS. Our data support universal Tier 4 carrier screening.

Prenatal sequencing of fetuses with abnormalities detected on imaging is expanding globally. Debate continues over whether variants of uncertain significance (VUS) should be reported prenatally, with some recent national position statements opposing this. In England, VUS that fit the fetal phenotype and require little further evidence for upgrade are discussed at multidisciplinary team (MDT) meetings to determine whether to report. We review the VUS reported by one English laboratory that provides prenatal sequencing to half of England. The laboratory's database was searched from 01/10/2020 to 30/04/2025 to ascertain all cases where a VUS was reported. Pregnancy outcomes were obtained from local clinical teams to determine whether the VUS status had been resolved. VUS were reported in 41/881 fetuses sequenced. Follow-up data were available for 38/41 cases, of which 23 were subsequently upgraded to likely pathogenic and 1 downgraded to likely benign. The most common reason for upgrade was new information from post-mortem or postnatal review (17/23). There is clinical utility in reporting VUS from prenatal sequencing following MDT discussion. Although reporting VUS leaves parents with uncertainty, follow up (including post-mortem when applicable) resolves this in over 50% of cases (79% of cases re-examined pre- or postnatally).