Mid-trimester Ultrasound Scan Research Articles

Automatic Deep Learning-Based Pipeline for Automatic Delineation and Measurement of Fetal Brain Structures in Routine Mid-Trimester Ultrasound Images

Introduction: The aim of this study was to develop a pipeline using state-of-the-art deep learning methods to automatically delineate and measure several of the most important brain structures in fetal brain ultrasound (US) images. Methods: The dataset was composed of 5,331 images of the fetal brain acquired during the routine mid-trimester US scan. Our proposed pipeline automatically performs the following three steps: brain plane classification (transventricular, transthalamic, or transcerebellar plane); brain structures delineation (9 different structures); and automatic measurement (from the structure delineations). The methods were trained on a subset of 4,331 images and each step was evaluated on the remaining 1,000 images. Results: Plane classification reached 98.6% average class accuracy. Brain structure delineation obtained an average pixel accuracy higher than 96% and a Jaccard index higher than 70%. Automatic measurements get an absolute error below 3.5% for the four standard head biometries (head circumference, biparietal diameter, occipitofrontal diameter, and cephalic index), 9% for transcerebellar diameter, 12% for cavum septi pellucidi ratio, and 26% for Sylvian fissure operculization degree. Conclusions: The proposed pipeline shows the potential of deep learning methods to delineate fetal head and brain structures and obtain automatic measures of each anatomical standard plane acquired during routine fetal US examination.

Childhood Outcomes in Children with and without Cardiac Echogenic Foci: An Electronic Birth Cohort Study in Wales, UK.

There is uncertainty about outcomes associated with cardiac echogenic foci (CEF) seen at the midtrimester ultrasound scan because of limited population-based follow-up data. This can lead to unnecessary invasive testing and significant parental anxiety. We analysed data from a cohort study, The Welsh Study of Mothers and Babies, to examine whether children with CEF had more adverse outcomes during childhood compared with children without CEF. Children born between 1 January 2009 and 31 December 2011 were followed until 31 January 2018, migration out of Wales, or death. The primary outcome was cardiac hospital admissions, defined a priori by an expert steering group. Secondary outcomes included congenital cardiac anomalies, and hospital admissions for other causes. There was no evidence of an association between isolated CEF and cardiac hospital admissions (hazard ratio 0.87, 95% confidence interval [CI] 0.33-2.25, p value 0.768), or with congenital cardiac anomalies. There was a small increased risk of a respiratory admission with isolated CEF (hazard ratio 1.27, 95% CI 1.04-1.54, p value 0.020). Further research is needed on features of CEF, such as location or number, to fully understand the clinical significance of these findings.

Short cervix and preterm birth in the top end.

Reducing rates of preterm birth (PTB) remains a significant challenge. The Northern Territory (NT) records some of the highest rates of PTB in the country, especially in First Nations women. In 2014, a Western Australian (WA) preterm birth prevention initiative involved the implementation of seven key initiatives. One of these was routine mid-trimester cervical length measurement. The initiative successfully reduced PTB rates following its first year of implementation. This was the first successful reduction in PTB, including the earlier gestational ages, across a population. To assess the uptake of routine cervical length measurement in the Top End of the NT after the success of the WA PTB prevention initiative and assess if treatment of a short cervix improved PTB rates. A retrospective cohort study of all women who received antenatal care and delivered their baby at the NT's only tertiary hospital was performed. Mid-trimester ultrasound scan data were collected from two separate time windows, before and after the implementation of the WA intervention. Treatments and gestational age at birth were recorded. Adoption of routine screening of cervical length measurement at mid-trimester ultrasound in the NT was successful, increasing from 4 to 88%. Detection rates of short cervix doubled. However, there was no difference to PTB rates despite targeted management. PTB remains a significant challenge in the NT, especially for First Nations women who are found to have a short cervix more commonly than non-Indigenous women in the Top End.

Accuracy of Mid-Trimester Ultrasound Scan in Foetal Gender Determination at the University College Hospital, Ibadan Nigeria

Objectives: This study aimed to determine the accuracy of prenatal sonographic gender determination during foetal anomaly ultrasound and the overall sensitivity pattern in our institution.
 Materials and Methods: A cross-sectional study of 520 consenting pregnant women who presented for foetal anomaly scans within a one-year period in our institution. The diagnostic accuracy of gender determination during the anomaly and delayed scans were determined by comparing the sonographic gender with the birth gender and calculating sensitivity, specificity, positive predictive value and negative predictive value. Data were analyzed using the Statistical Package for Social Sciences (SPSS) version 20. Descriptive statistics, frequencies, Mc-Nemar chi-square test were used at 5% level of significance.
 Results: The mean maternal age was 31.51 ±5.02years. Of the 520 consenting pregnant women studied, 16(6.0%) women were having twin gestation. Four hundred and ninety-seven (92.7%) genders were determined during foetal anomaly scan. The accuracy of the ultrasonography (US) examination performed by the resident doctors was 98.02% while the accuracy of the scan performed by the consultant radiologists was 100%. Overall, the accuracy of the gender determination on ultrasound was 98.69%. The general specificity and sensitivity of the US were 98.71 % and 98.68% respectively while the positive and negative predictive value were 99.01 % and 98.29% respectively.
 Conclusion: The accuracy of ultrasound examination in detecting foetal gender during foetal anomaly ultrasound is high with equally high predictive values and therefore it is recommended as a mandatory variable during anomaly scans. There is need for continuous training of resident doctors or operators in lower cadre to improve their competency in foetal gender determination.

Accuracy of Mid-Trimester Ultrasound Scan in Foetal Gender Determination at the University College Hospital, Ibadan Nigeria

Objectives: This study aimed to determine the accuracy of prenatal sonographic gender determination during foetal anomaly ultrasound and the overall sensitivity pattern in our institution.
 Materials and Methods: A cross-sectional study of 520 consenting pregnant women who presented for foetal anomaly scans within a one-year period in our institution. The diagnostic accuracy of gender determination during the anomaly and delayed scans were determined by comparing the sonographic gender with the birth gender and calculating sensitivity, specificity, positive predictive value and negative predictive value. Data were analyzed using the Statistical Package for Social Sciences (SPSS) version 20. Descriptive statistics, frequencies, Mc-Nemar chi-square test were used at 5% level of significance.
 Results: The mean maternal age was 31.51 ±5.02years. Of the 520 consenting pregnant women studied, 16(6.0%) women were having twin gestation. Four hundred and ninety-seven (92.7%) genders were determined during foetal anomaly scan. The accuracy of the ultrasonography (US) examination performed by the resident doctors was 98.02% while the accuracy of the scan performed by the consultant radiologists was 100%. Overall, the accuracy of the gender determination on ultrasound was 98.69%. The general specificity and sensitivity of the US were 98.71 % and 98.68% respectively while the positive and negative predictive value were 99.01 % and 98.29% respectively.
 Conclusion: The accuracy of ultrasound examination in detecting foetal gender during foetal anomaly ultrasound is high with equally high predictive values and therefore it is recommended as a mandatory variable during anomaly scans. There is need for continuous training of resident doctors or operators in lower cadre to improve their competency in foetal gender determination.

Expected-value bias in mid-trimester preterm birth screening.

Cervical length (CL) measurement ≤ 25 mm on mid-trimester ultrasound scan is a known risk factor for preterm birth, for which vaginal progesterone is recommended. The aims of this study were to evaluate whether CL measurement is affected by observer bias and to assess the impact on short cervix prevalence of masking CL measurement during routine mid-trimester ultrasound scan. This was a flash study designed for a 2-month period (October and November 2018) at Cruces University Hospital (Bizkaia, Spain), in which all CL measurements from routine mid-trimester scans were masked. During the study period, there was no modification of the routine screening method, and women with a short cervix were prescribed 200 mg vaginal progesterone daily as per usual. The control group included women examined in a 2-month period (April and May 2018) prior to the study, in which CL measurements were taken as usual by a non-blinded operator. The primary outcome was the prevalence of short cervix in each group. A total of 983 CL measurements were analyzed, including 457 in the blinded group and 526 in the control group. The prevalence of short cervix was 2.7% in the non-blinded group and 5.5% in the blinded group (P = 0.024). We identified a statistically significant difference in the incidence of CL of 24-25 mm between the two groups, with a lower prevalence in the non-blinded vs blinded group (0.6% vs 2.4%; P < 0.005). Moreover, the distribution of CL values was normal in the blinded group, in contrast to the non-blinded group, which was characterized by skewed distribution of CL values. Expected-value bias exists and should be taken into account when measuring CL in mid-trimester preterm birth screening. Blinding has demonstrated to be an effective strategy to improve the performance of CL screening in clinical practice. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Accuracy of the mid-trimester ultrasound scan in the detection of fetal congenital anomalies in a reference center in Northeastern Brazil

ObjectiveTo assess the performance of a basic mid-trimester fetal ultrasound scan protocol for the diagnosis of congenital anomalies by calculating its accuracy, sensitivity, and specificity. MethodsThis longitudinal cohort study involved singleton pregnant women recruited at the mid-trimester fetal ultrasound scan through the postnatal evaluation of congenital anomalies. Pregnant women who underwent a routine mid-trimester ultrasound scan for fetal abnormalities at 20–24 weeks of gestation were enrolled in this study. After childbirth, we searched their medical records on gestational outcomes and neonatal examination records, as well as complementary medical examinations, to assess the ultrasound performance in diagnosing congenital malformations. ResultsWe included 967 pregnant women in the study population, and prenatal ultrasound scans detected congenital abnormalities in 67 fetuses (6.9%). Among newborns, 54 (5.6%) were postnatally diagnosed with malformations. The overall sensitivity and specificity of the mid-trimester ultrasound scan for congenital malformation detection were 61.1% and 96.3%, respectively, with an accuracy of 94.3% (p < .05). ConclusionThe mid-trimester ultrasound scan had good accuracy in the detection of congenital malformations, although the overall sensitivity does not support it as the only screening test for anomalies throughout pregnancy.

WAPM-World Association of Perinatal Medicine practice guidelines: fetal central nervous system examination

These practice guidelines follow the mission of the World Association of Perinatal Medicine (WAPM) in collaboration with the Perinatal Medicine Foundation, bringing together groups and individuals throughout the world, with the goal of improving the ultrasound assessment of the fetal central nervous system (CNS) anatomy. In fact, this document provides further guidance for healthcare practitioners for the evaluation of the fetal CNS during the mid-trimester ultrasound scan with the aim to increase the ability in evaluating normal fetal anatomy. Therefore, it is not intended to establish a legal standard of care. This document is based on consensus among perinatal experts throughout the world, and serves as a guideline for use in clinical practice.

WAPM-World Association of Perinatal Medicine Practice Guidelines: Fetal central nervous system examination.

These practice guidelines follow the mission of the World Association of Perinatal Medicine in collaboration with the Perinatal Medicine Foundation, bringing together groups and individuals throughout the world, with the goal of improving the ultrasound assessment of the fetal Central Nervous System (CNS) anatomy. In fact, this document provides further guidance for healthcare practitioners for the evaluation of the fetal CNS during the mid-trimester ultrasound scan with the aim to increase the ability in evaluating normal fetal anatomy. Therefore, it is not intended to establish a legal standard of care. This document is based on consensus among perinatal experts throughout the world, and serves as a guideline for use in clinical practice.

Accuracy of prenatal ultrasound in the diagnosis of corpus callosum anomalies

Objectives: The main objective of this study was to evaluate the accuracy of prenatal ultrasound to diagnose corpus callosum alterations, compared to prenatal magnetic resonance imaging (MRI), postnatal image techniques (ultrasound and/or MRI), and post-mortem examination in terminated pregnancies.Methods: Retrospective review of 86 cases of prenatal ultrasound diagnosis of corpus callosum anomalies between January 2007 and December 2015 at a third level Maternal Fetal Medicine center. The study reviewed the findings of prenatal ultrasound and MRI, post-mortem examination in cases of termination of pregnancy (TOP) or stillbirths and postnatal ultrasound, and MRI in neonates. The anomalies of corpus callosum (CC) were classified as complete agenesis of the corpus callosum (ACC), partial ACC, or dysgenesis of CC.Results: Fifty-eight (67.4%) cases resulted in TOP, 26 (30.2%) cases opted to continue with the pregnancy and two (2.3%) cases were lost to follow up. Among the 26 cases that continued with the pregnancy, 24 (92.3%) were live births and two (7.7%) were stillborn. All cases in which a third trimester MRI was performed (n = 46) confirmed the prenatal ultrasound diagnosis of CC anomaly. In seven (15.2%) of them, the MRI found additional intracranial findings and in three cases (6.5%) the type of CC anomaly (complete, partial, or dysgenesis) was reclassified (Kappa index: 0.86, 95% CI: 0.71–1.00). CC anomalies were confirmed in 46 (95.8%) of the 48 cases in which a post-mortem examination was available, the type of anomaly being reclassified in three cases (6.3%) (Kappa index: 0.88, 95% CI: 0.75–1.00). Among the 10 cases in which a postnatal ultrasound was performed, the CC anomaly was confirmed in all and the type of anomaly was reclassified in 1 (10%) of them (Kappa index: 0.75, 95% CI: 0.32–1.00).Conclusion: Corpus callosum agenesis can be detected on the routine mid-trimester ultrasound scan. Prenatal ultrasound and MRI can accurately classify the type of CC abnormality. Moreover, third trimester MRI can detect additional intracranial anomalies in 15% of cases.

The Evaluation of Uterine Leiomyoma Prevalence and Its Effect on Cervical Length During Mid-Trimester Ultrasound Scan

The Evaluation of Uterine Leiomyoma Prevalence and Its Effect on Cervical Length During Mid-Trimester Ultrasound Scan

Skeletal defect at mid-trimester ultrasound scan

Skeletal defect at mid-trimester ultrasound scan

Four Steps in Diagnosing Complete Agenesis oftheCorpus Callosum in Prenatal Life.

Among congenital brain anomalies, complete agenesis of the corpus callosum (cACC) including cases of callosal hypoplasia has a prevalence of 1.8 per 10 000 in the general population. It is also one of the most challenging brain anomalies to detect during the mid-trimester ultrasound scan. Standard axial planes do not provide enough information to make the definitive diagnosis of cACC. From our library of images and ultrasound reports, we reviewed our most recent cases of complete agenesis of the corpus callosum in the fetus at the mid-trimester scan. In our analysis we included only cases that were confirmed postnatally or by autopsy. Exams were performed between January 2010 and June 2012. All of the patients were scanned transabdominally by means of 2 D and static 3 D. From the 2 D and 3 D images we identified 4 anatomical views that consistently gave us enough information to identify cACC: axial biparietal transthalamic view (AX1); axial biparietal falx view (AX2); coronal transthalamic view (COR); mid-sagittal view (SAG). From our library 30 cases were selected with confirmed cACC postnatally or in autopsy findings. The mean gestational age at the time of referral to our center was 20.7 weeks (range 19 - 23 weeks). In all analyzed cases sufficient 2 D images were found and in 93.3 % of them informative 3 D volumes were also available for off-line review. We identified the following patterns of cACC at the mid-trimester scan: A- normal size of 3 rd ventricle + normal size of the lateral ventricles or mild ventriculomegaly; B1- dilated 3 rd ventricle + normal size of the lateral ventricles; B2- dilated 3 rd ventricle + mild or moderate ventriculomegaly; C- dilated 3 rd ventricle + severe ventriculomegaly; D- gross dilatation of 3 rd ventricle with the appearance of interhemispheric cyst. The AX1 view revealed: absence of the cavum septum pellucidi in all cases; dilatation of the third ventricle in 86.6 % of cases; separation of frontal horns in 83.3 % of cases; ventriculomegaly in 73.3 % of cases, including 13.6 % with severe forms. The AX2 view showed separation of the interhemispheric fissure (IHF) in 90 % of cases and upward displacement of the 3 rd ventricle in 80 % of cases. The COR view confirmed separation of the interhemispheric fissure in 90 % of cases including gross separation in 7.4 % of cases; absence of CC fibers at this level and descent of the falx towards the roof of the 3 rd ventricle in all cases, and upward displacement of the 3 rd ventricle in 80 % of cases. The SAG view revealed the absence of the CSP-CC complex in all cases and dilatation of the 3 rd ventricle in 86.6 % of cases. 1. We suggest a stepwise ultrasound diagnostic approach for cACC and variations of this condition. 2. We suggest a classification of characteristic patterns found in fetuses with proven cACC based on findings presented in axial views.

Relationship of Isolated Single Umbilical Artery to Fetal Growth, Aneuploidy, and Perinatal Mortality

The umbilical cord normally contains 2 arteries and a single vein. When an umbilical artery is absent, the condition is called single umbilical artery (SUA). The reported prevalence of SUA varies from 0.5% at the second-trimester prenatal ultrasound and in umbilical cord specimens from live-born infants to 2.1% in fetal deaths, autopsies, or aborted fetuses. Approximately 33% of fetuses with SUA have additional structural anomalies, and 10% are affected with aneuploidy. In ~65% of cases, SUA seems to be an isolated finding. In pregnancies with an apparently isolated SUA (iSUA), aneuploidy or fetal size (small for gestational age [SGA]) may become apparent later in pregnancy or at birth. This systematic review was undertaken to assess outcome of iSUA diagnosed at the midtrimester ultrasound scan and to determine whether data are sufficient to determine appropriate management of pregnancies with diagnosed iSUA. MEDLINE, EMBASE, and the Cochrane Library databases were searched for articles reporting on SUA. Randomized controlled trials, cohort studies, and case-control studies were eligible if they described 30 or more cases of apparent iSUA identified by ultrasound before a mean gestational age of 24 weeks. All studies that allowed construction of a 2 × 2 table were included, with the incidence of the outcome of interest in SUA fetuses and 3-vessel cord fetuses. Quantitative data on the outcome variables included incidence of SGA and perinatal mortality, median or mean birth weight, and frequency of aneuploidy. Odds ratios (ORs) with 95% confidence intervals (CIs) were determined for the occurrence of SGA, perinatal mortality, and frequency of aneuploidy in iSUA fetuses compared with those in 3-vessel cord fetuses. Of 449 articles, the final analysis included 3 cohort and 4 case-control studies, reporting on 68 and 297 cases of apparent iSUA, with a total of 982 patients with an iSUA. The mean gestational age at diagnosis of SUA was 19.0 to 24.3 weeks. A non–statistically significant association was found between iSUA and SGA at birth (OR for SGA in fetuses with iSUA, 1.6; 95% CI, 0.97–2.6; P = 0.06), with ORs in the cohort studies ranging from 1.1 to 3.3. In 3 of the case-control studies, iSUA fetuses did not have significantly lower mean birth weights compared with control fetuses (mean weight, 3154 vs 3176 g; mean difference, 51 g; 95% CI, −154.7 to 52.6 g; P = 0.33). The OR for preterm birth in fetuses with an iSUA compared with control fetuses was 2.1 (95% CI, 1.4–3.2) for delivery before 37 weeks and 3.3 (95% CI, 1.4–7.7) for delivery before 34 weeks. Although there was a positive association between iSUA and increased perinatal mortality, it did not meet statistical significance (OR, 2.0; 95% CI, 0.9–4.2; P = 0.07). Among 695 iSUA cases reported in 16 studies, 4 cases of aneuploidy (0.58%) occurred; the mean maternal age was 30.1 years. These results indicate that iSUA is associated with a nonsignificant trend for increased risk for SGA and perinatal mortality. The relatively low birth weight in iSUA neonates may occur as a result of a relatively high prevalence of preterm birth. On the basis of this review, no firm conclusions can be drawn about the association between iSUA and aneuploidy. More large-scale, prospective cohort studies are necessary to clarify these associations and identify appropriate management protocols for iSUA fetuses.

Knowledge, Expectations and Source of Information of Pregnant Saudi Women Undergoing Second Trimester Ultrasound Examination

Background: In Saudi Arabia, most antenatal units offer routine Ultrasound Scan (USS) in early and mid-trimester of pregnancy. USS examination is essential source of information for the obstetrical management of the pregnancy as well as a source of joy and reassurance for the mother about the wellbeing of her baby. Methods: A cross-sectional survey was conducted at the obstetrics ultrasound department at King Khalid University Hospital in Riyadh, Saudi Arabia. A questionnaire was designed to investigate the knowledge of the mothers about the purpose of the USS, their expectations and the source of the information provided to them about the mid-trimester USS examination in addition to the respondents demographic characteristics. Descriptive statistics were used for demographic variables. Association between women’s source of information and educational level was analyzed with chi-square test. P<0.05 was considered significant. Results: 600 women consented and completed the questionnaire. Most of the participants were 21-30 years of age and (51.4%) had university education or higher while only 1.8% of the respondents were illiterate. 28-30% of the respondents thought the purpose of the scan is to know the gender of the baby or to confirm that the baby is alive. Only 20% of the respondents reported purposes of the USS examination was to screen for congenital malformations. The obstetrician was the main source of information and the nurse was the least. The utilization of any source of information about USS examination increased with the increase of the level of maternal education. Conclusion: Saudi mothers’ knowledge about the purpose of mid-trimester USS is modest. Utilization of healthcare providers other than the obstetrician and contemporary technology for information provision will improve mothers’ knowledge and choices and put them at the center of health care.

Solitary median maxillary central incisor (SMMCI) syndrome

Solitary median maxillary central incisor syndrome (SMMCI) is a complex disorder consisting of multiple, mainly midline defects of development resulting from unknown factor(s) operating in utero about the 35th–38th day(s) from conception. It is estimated to occur in 1:50,000 live births. Aetiology is uncertain. Missense mutation in the SHH gene (I111F) at 7q36 may be associated with SMMCI. The SMMCI tooth differs from the normal central incisor, in that the crown form is symmetric; it develops and erupts precisely in the midline of the maxillary dental arch in both primary and permanent dentitions. Congenital nasal malformation (choanal atresia, midnasal stenosis or congenital pyriform aperture stenosis) is positively associated with SMMCI. The presence of an SMMCI tooth can predict associated anomalies and in particular the serious anomaly holoprosencephaly. Common congenital anomalies associated with SMMCI are: severe to mild intellectual disability, congenital heart disease, cleft lip and/or palate and less frequently, microcephaly, hypopituitarism, hypotelorism, convergent strabismus, oesophageal and duodenal atresia, cervical hemivertebrae, cervical dermoid, hypothyroidism, scoliosis, absent kidney, micropenis and ambiguous genitalia. Short stature is present in half the children. Diagnosis should be made by eight months of age, but can be made at birth and even prenatally at 18–22 weeks from the routine mid-trimester ultrasound scan. Management depends upon the individual anomalies present. Choanal stenosis requires emergency surgical treatment. Short stature may require growth hormone therapy. SMMCI tooth itself is mainly an aesthetic problem, which is ideally managed by combined orthodontic, prosthodontic and oral surgical treatment; alternatively, it can be left untreated.

Gestational age and induction of labour for prolonged pregnancy

To examine the length of gestation according to menstrual and ultrasound scan dates, and the rate of induction of labour in a unit with a routine induction policy for prolonged pregnancy. Retrospective analysis of computer files of 24,675 pregnancies delivered in a teaching hospital between 1988 and 1995, which had a record of the last menstrual period and a dating ultrasound scan. Detailed survey of 168 casenotes of consecutive inductions of labour to establish the indications given. Teaching hospital with policies of routine mid-trimester ultrasound scan and routine induction for prolonged pregnancy at 290 to 294 days. Gestational age at delivery by menstrual history and ultrasound biometry in spontaneous and induced labours. The single largest category of reasons given for induction of labour was prolonged pregnancy. 'Post-term pregnancy', from the date of expected delivery as recorded in the notes, together with 'maternal request' and 'social factors', were the reasons given for induction of labour in 71.3% of cases. Menstrual dates systematically overestimated gestational age at term when compared with scan dates. After 41 weeks, this difference exceeded the confidence limits for second trimester scan dating error, suggesting that most pregnancies which are considered 'prolonged' according to menstrual dates are in fact mis-dated. The median gestational age for induced labours was 286 days by last menstrual period but only 280 days by scan, and most (71.5%) inductions done post-term (> 294 days) according to menstrual dates were not post-term if scan dates alone are used to calculate the gestational age. The average induction rate over the seven year study period was 16.6%. It was higher when there was any gestational age error in either direction (16.8%) compared with when menstrual and scan dates were in complete agreement (13.7%, OR 1.27, CI 1.09-1.47, P < 0.001). The induction rate was highest (up to 21.8%) in the cases where menstrual dates overstated gestational age without exceeding the usual limits for adjusting dates according to scan. Such overestimation within tolerance limits of 7, 10 or 14 days occurred in 37.1%, 45.8%, or 52.6% of all pregnancies, respectively. Most pregnancies undergoing post-term induction are not post-term when assessed by ultrasound dates. Regardless of whether prolonged pregnancy is considered to be a risk factor requiring intervention, the proportion of pregnancies considered 'post-term' can be reduced considerably by a dating policy which ignores menstrual dates and establishes the expected delivery date on the basis of ultrasound dates alone.

Clinical significance of fetal choroid plexus cysts

Summary Choroid plexus (CP) cysts are commonly detected on routine mid-trimester ultrasound scan. When associated anomalies are detected, the risk is sufficient to justify an invasive diagnostic test such as amniocentesis. However, the risk when no associated anomalies are detected is much less well defined. This information is required to determine the appropriate management in cases of apparently isolated CP cysts. We thought the only way to resolve the difficulties in counselling prospective parents was to conduct a prospective study in a large unselected population. A registry of fetal CP cysts detected over 3 years in the Yorkshire Region was compiled and we identified 524 CP cysts. These cases were then amalgamated and analysed with 1361 cases from prospective studies reported in the world English literature and a further 71 unpublished cases identified from a 2 year prospective series from Ninewells Hospital, Dundee. The risk of chromosomal abnormalities was 1 in 150 (95% Cl 1 in 85, 1 in 261) when no fetal anatomic abnormalities, apart from the CP cysts themselves, were detected antenatally. The risk increased to approximately 1 in 3 if any other associated ultrasound abnormalities were detected antenatally. The risk did not appear to be related to whether or not cyst size diminished as gestation progresses, whether they were unilateral or bilateral, and whether they were small or large in size (60-80% <10 mm). 76% of aneuploidic cases were trisomy 18 and 17% were trisomy 21. The risk of Down's syndrome in fetuses with CP cysts but no other anomalies detected antenatally is 1 in 880. The probability of a chromosomal abnormality is high when CP cysts are associated with any other antenatally detected anomaly, indicating a clear need to offering amniocentesis. The predictive value is much lower when no other anomalies are detected. In such cases, it is probably advisable to regard CP cysts as an indication for detailed ultrasound assessment, rather than invasive testing.