Embryonic statistical analyses reveal 2 growth phenotypes in mouse models of Down syndrome

BACKGROUND

Down syndrome is associated with several comorbidities, including intellectual disability, growth restriction, and congenital heart defects. The prevalence of Down syndrome-associated comorbidities is highly variable, and intellectual disability, although fully penetrant, ranges from mild to severe. Understanding the basis of this interindividual variability might identify predictive biomarkers of in utero and postnatal outcomes that could be used as endpoints to test the efficacy of future therapeutic interventions.

OBJECTIVE

The main objective of this study was to examine if antenatal interindividual variability exists in mouse models of Down syndrome and whether applying statistical approaches to clinically relevant measurements (ie, the weights of the embryo, placenta, and brain) could define cutoffs that discriminate between subgroups of trisomic embryos.

STUDY DESIGN

Three commonly used mouse models of Down syndrome (Dp(16)1/Yey, Ts65Dn, and Ts1Cje) and a new model (Ts66Yah) were used in this study. Trisomic and euploid littermate embryos were used from each model with total numbers of 102 for Ts66Yah, 118 for Dp(16)1/Yey, 92 for Ts65Dn, and 126 for Ts1Cje. Placental, embryonic, and brain weights and volumes at embryonic day 18.5 were compared between genotypes in each model. K-mean clustering analysis was applied to embryonic and brain weights to identify severity classes in trisomic embryos, and brain and placental volumetric measurements were compared between genotypes and classes for each strain. In addition, Ts66Yah embryos were examined for malformations because embryonic phenotypes have never been examined in this model.

RESULTS

Reduced body and brain weights were present in Ts66Yah, Dp(16)1/Yey, and Ts65Dn embyos. Cluster analysis identified 2 severity classes in trisomic embryos-mild and severe-in all 4 models that were distinguishable using a putative embryonic weight cutoff of <0.5 standard deviation below the mean. Ts66Yah trisomic embryos develop congenital anomalies that are also found in humans with Down syndrome, including congenital heart defects and renal pelvis dilation.

CONCLUSION

Statistical approaches applied to clinically relevant measurements revealed 2 classes of phenotypic severity in trisomic mouse models of Down syndrome. Analysis of severely affected trisomic animals may facilitate the identification of biomarkers and endpoints that can be used to prenatally predict outcomes and the efficacy of treatments.

Clinical implications of crown-rump length discordance at 11 to 14 weeks in dichorionic twins

BACKGROUND

Crown-rump length discordance, defined as ≥10% discordance, has been investigated as an early sonographic marker of subsequent growth abnormalities and is associated with an increased risk of fetal loss in twin pregnancies. Previous studies have not investigated the prevalence of fetal aneuploidy or structural anomalies in twins with discordance or the independent association of crown-rump length discordance with adverse perinatal outcomes. Moreover, data are limited on cell-free DNA screening for aneuploidy in dichorionic twins with discordance.

OBJECTIVE

This study aimed to evaluate whether crown-rump length discordance in dichorionic twins between 11 and 14 weeks of gestation is associated with a higher risk of aneuploidy, structural anomalies, or adverse perinatal outcomes and to assess the performance of cell-free DNA screening in dichorionic twin pregnancies with crown-rump length discordance.

STUDY DESIGN

This was a secondary analysis of a multicenter retrospective cohort study that evaluated the performance of cell-free DNA screening for the common trisomies in twin pregnancies from December 2011 to February 2020. For this secondary analysis, we included live dichorionic pregnancies with crown-rump length measurements between 11 and 14 weeks of gestation. First, we compared twin pregnancies with discordant crown-rump lengths with twin pregnancies with concordant crown-rump lengths and analyzed the prevalence of aneuploidy and fetal structural anomalies in either twin. Second, we compared the prevalence of a composite adverse perinatal outcome, which included preterm birth at <34 weeks of gestation, hypertensive disorders of pregnancy, stillbirth or miscarriage, small-for-gestational-age birthweight, and birthweight discordance. Moreover, we assessed the performance of cell-free DNA screening in pregnancies with and without crown-rump length discordance. Outcomes were compared with multivariable regression to adjust for confounders.

RESULTS

Of 987 dichorionic twins, 142 (14%) had crown-rump length discordance. The prevalence of aneuploidy was higher in twins with crown-rump length discordance than in twins with concordance (9.9% vs 3.9%, respectively; adjusted relative risk, 2.7; 95% confidence interval, 1.4-4.9). Similarly, structural anomalies (adjusted relative risk, 2.5; 95% confidence interval, 1.4-4.4]) and composite adverse perinatal outcomes (adjusted relative risk, 1.2; 95% confidence interval, 1.04-1.3) were significantly higher in twins with discordance. A stratified analysis demonstrated that even without other ultrasound markers, there were increased risks of aneuploidy (adjusted relative risk, 3.5; 95% confidence interval, 1.5-8.4) and structural anomalies (adjusted relative risk, 2.7; 95% confidence interval, 1.5-4.8) in twins with CRL discordance. Cell-free DNA screening had high negative predictive values for trisomy 21, trisomy 18, and trisomy 13, regardless of crown-rump length discordance, with 1 false-negative for trisomy 21 in a twin pregnancy with discordance.

CONCLUSION

Crown-rump length discordance in dichorionic twins is associated with an increased risk of aneuploidy, structural anomalies, and adverse perinatal outcomes, even without other sonographic abnormalities. Cell-free DNA screening demonstrated high sensitivity and negative predictive values irrespective of crown-rump length discordance; however, 1 false-negative result illustrated that there is a role for diagnostic testing. These data may prove useful in identifying twin pregnancies that may benefit from increased screening and surveillance and are not ascertained by other early sonographic markers.

Immunological Role of the Maternal Uterine Microbiome in Pregnancy: Pregnancies Pathologies and Alterated Microbiota

Understanding what happens at the time of embryo implantation has been the subject of significant research. Investigators from many differing fields including maternal fetal medicine, microbiology, genetics, reproductive endocrinology and immunology have all been studying the moment the embryo interacts with the maternal endometrium. A perfect relationship between the uterus and the embryo, mediated by a tightly controlled interaction between the embryo and the endometrium, is required for successful implantation. Any factors affecting this communication, such as altered microbiome may lead to poor reproductive outcomes. Current theories suggest that altered microbiota may trigger an inflammatory response in the endometrium that affects the success of embryo implantation, as inflammatory mediators are tightly regulated during the adhesion of the blastocyst to the epithelial endometrial wall. In this review, we will highlight the various microbiome found during the periconceptual period, the microbiomes interaction with immunological responses surrounding the time of implantation, its effect on implantation, placentation and ultimately maternal and neonatal outcomes.

Influence of distribution of mother's abdominal body fat on first trimester fetal growth

Objective: Fetal growth in the first trimester is estimated by measuring the crown to rump length of the fetus (CRL). There are no data on the relation between fetal growth and fat distribution in pregnant women. The objective was to investigate the influence of fat distribution in pregnant women on fetal growth in the first trimester of pregnancy.Methods: This was a controlled observation using a random sampling method. Newly registered pregnant women were included in the sample during a 12-18-month period. The study included 400 pregnant women from Bjelovarsko-bilogorska County, Croatia. Participants were divided into three groups according to their pregravid BMI values, normal weight (n = 254), overweight (n = 103), and obese (n = 43). In the 12th week of pregnancy, the CRL was measured by transvaginal ultrasound. The subcutaneous and preperitoneal fat was measured by transabdominal ultrasound, using the Suzuki method. The correlation was tested by the Pearson's coefficient, and a linear regression analysis was performed on the variables with good correlation.Results: In normal weight pregnant women, there is no correlation between the adipose tissue and fetal length, but there is a significant correlation between overweight and obese ones.Conclusion: The distribution of adipose tissue in obese and overweight pregnant women is associated with fetal length in the first trimester of pregnancy, with a stronger correlation between visceral fat and fetal length. The influence of this correlation on the overall fetal growth should be investigated by longitudinal monitoring of these variables during the entire pregnancy.

Expanded conventional first trimester screening

Objective

The study aims to determine the performance of a five (5) serum marker plus ultrasound screening protocol for T21, T18 and T13.

Method

Specimens from 331 unaffected, 34 T21, 19 T18 and 8 T13 cases were analyzed for free Beta human chorionic gonadotropin, pregnancy‐associated plasma protein A, alpha‐fetoprotein, placental growth factor and dimeric inhibin A. Gaussian distributions of multiples of the median values were used to estimate modeled false positive and detection rates (DR).

Results

For T21, at a 1/300 risk cut‐off, DR of screening with all five serum markers along with nuchal translucency and nasal bone was 98% at a 1.2% false positive rate (FPR). Using a 1/1000 cut‐off, the DR was 99% with a 2.6% FPR. For T18/13 with free Beta human chorionic gonadotropin, pregnancy‐associated plasma protein A, placental growth factor and nuchal translucency at a 1/150 cut‐off, DR was 95% at a 0.5% FPR while at a 1/500 risk cut‐off, DR was 97% at a 1.2% FPR.

Conclusion

An expanded conventional screening test can achieve very high DRs with low FPRs. Such screening fits well with proposed contingency protocols utilizing cell‐free DNA as a secondary or reflex but also provides the advantages of identification of pregnancies at risk for other adverse outcomes such as early‐onset preeclampsia. © 2017 Eurofins NTD, LLC. Prenatal Diagnosis published by John Wiley & Sons, Ltd.

What's already known about this topic?

Conventional Down syndrome screening with ultrasound markers and free Beta hCG and PAPP‐A has been successfully utilized for nearly 20 years to screen for trisomies 21, 18 and 13.

Cell‐free DNA screening has much higher detection and lower false positive rates but is expensive.

What does this study add?

An expanded conventional screen with nuchal translucency and nasal bone that includes additional serum markers AFP, placental growth factor and dimeric inhibin A can detect 98% of trisomy 21 and 95% of trisomy 18/13 cases at a false positive rate of 1.2% and 0.5%, respectively.

Offering cell‐free DNA testing to those patients found at increased risk with the expanded screen maintains the detection efficiency but brings the invasive testing rate to an exceedingly low level.

Down syndrome birth weight in England and Wales: Implications for clinical practice

The aim of this study was to determine if syndrome‐specific birth weight charts were beneficial for babies with Down syndrome in England and Wales. Birth weights of 8,825 babies with Down syndrome born in England and Wales in 1989–2010 were obtained from the National Down Syndrome Cytogenetic Register. Birth weight centiles for 30–42 weeks gestation by sex were fitted using the LMS method and were compared to those for unaffected babies from the UK‐WHO growth charts. For babies born with Down syndrome the median birth weight from 37 to 42 weeks was 2,970 g (10th–90th centile: 2,115–3,680) for boys and 2930 g (2,100–3,629) for girls, and the modal age of gestation was 38 weeks, 2 weeks earlier than for unaffected babies. At 38 weeks gestation they were only slightly lighter than unaffected babies (159 g for boys and 86 g for girls). However at 40 weeks gestation the shortfall was much greater (304 g and 239 g, respectively). In neonates with Down syndrome there is little evidence of growth restriction before 38 weeks gestation, so up to this age it is appropriate to use the UK‐WHO birth weight charts. Thereafter birth weight is below that of unaffected babies and it should be plotted on the UK Down syndrome growth charts. © 2015 The Authors. American Journal of Medical Genetics Part A Published by Wiley Periodicals, Inc.

First-trimester crown-rump length and embryonic volume of aneuploid fetuses measured in virtual reality

OBJECTIVES

To examine whether embryonic volume (EV), as measured using three-dimensional (3D) ultrasound and a virtual reality approach, is a better measure of growth restriction than is crown-rump length (CRL) in aneuploid fetuses.

METHODS

We retrospectively measured CRL and EV in prospectively collected 3D ultrasound volumes of 55 aneuploid fetuses using the Barco I-Space VR system. The gestational age ranged from 11 + 2 to 14 + 4 weeks. We compared our measured data with previously published reference curves for euploid fetuses. Delta-values were calculated by subtracting the expected mean for euploid fetuses of the same gestational age from observed values. The one-sample t-test was used to test the significance of differences observed.

RESULTS

The CRL measurements of fetuses with trisomy 21 (n = 26), trisomy 13 (n = 5) and monosomy X (n = 5) were comparable with those of euploid fetuses, but in fetuses with trisomy 18 (n = 19) the CRL was 14.5% smaller (P < 0.001). The EV in fetuses with trisomies 21, 18 and 13 and monosomy X was smaller than in euploid fetuses (-27.8%, P < 0.001; -39.4%, P < 0.001; -40.9%, P = 0.004; and -27.3%, P = 0.055, respectively).

CONCLUSIONS

When relying on CRL measurements alone, first-trimester growth restriction is especially manifest in trisomy 18. Using EV, growth restriction is also evident in trisomies 21 and 13 and monosomy X. EV seems to be a more effective measurement for the assessment of first-trimester growth restriction in aneuploid fetuses.

The K-P algorithm: a new first-trimester growth model - comparison with other formulae and correlations with recorded embryonic lengths

OBJECTIVE

To generate and validate individually fitted first-trimester growth curves using a new growth model. Secondary aims were to compare this new model with actual recorded embryonic measurements and validate its predictive accuracy.

METHODS

A prospective study of women presenting to the Early Pregnancy Unit in the first trimester. Women with viable singleton pregnancies at the end of the first trimester who had had at least two crown-rump length (CRL) measurements were selected. An individual power function of CRL was derived from serial CRL measurements. Individual curves were fitted using computer software to estimate a dating adjustment factor ('k'), and a growth coefficient ('P') for each case. The predictive accuracy of the growth curves was then tested in a validation subset of the population that had a third CRL measurement. The population average curve from the developed model was also extrapolated to day 27 menstrual age (Carnegie stage 6), day 30 menstrual age (Carnegie stage 7) and day 84 menstrual age, and values were compared to previously reported measurements.

RESULTS

326 viable pregnancies were selected for CRL growth curve development. The mean time interval between CRL measurements was 20.5 days (range 2-44). The mean value for 'P' was 2.058, and for 'k' 24.6. Testing the model on a subset of 81 cases showed that the average error in predicting a third CRL measurement was 1% (SD 9.1%).

CONCLUSIONS

These new, individually fitted growth curves for the first trimester correlate more closely with the recorded embryonic lengths than other standards.

Anthropometric charts for infants with trisomies 21, 18, or 13 born between 22 weeks gestation and term: the VON charts

Data on birth weight for gestational age (GA) are not well described for infants with trisomy 21 (T21), trisomy 18 (T18), or trisomy 13 (T13). We report on anthropometric charts of infants with these conditions using data from the Vermont Oxford Network (VON). Data from a total of 5,147 infants with T21 aged 22-41 weeks, 1,053 infants with T18 aged 22-41 weeks, and 613 infants with T13 aged 22-40 weeks were used to create birth weight for GA charts. Head circumference for GA charts were created for infants with T21 only. Combined-sex charts were generated for infants with T18 or T13 while sex-specific charts were generated for infants with T21. Smoothed centiles were created using LmsChartMaker Pro 2.3. Among the three examined groups, infants with T18 were the most likely to be growth restricted while infants with T21 were the least likely to be growth restricted. The new charts for infants with T21 were also compared to the Lubchenco and Fenton charts and both show frequent misclassification of infants with T21 as small or large for GA. The new charts should prove to be useful, especially for infants with T21, to assist in medical management and guide nutrition care decisions.

Prenatal sonographic features of fetuses in trisomy 13 pregnancies. IV

Prenatal ultrasound is a powerful tool to detect structural abnormalities associated with the fetuses in trisomy 13 pregnancies. This article provides a comprehensive review of the prenatal sonographic markers of trisomy 13 in the first trimester, including fetal nuchal translucency thickness, fetal heart rate, fetal nasal bone, fetal tricuspid regurgitation, ductus venous flow, fetal crown-rump length, fetal trunk and head volume, fetal frontomaxillary facial angle, gestational sac volume and umbilical cord diameter, along with biochemical markers such as maternal serum free beta-human chorionic gonadotropin, maternal serum pregnancy-associated plasma protein-A, maternal serum placental growth factor, and the fetal and total cell-free DNA concentration in the maternal circulation.

An innovative virtual reality technique for automated human embryonic volume measurements

BACKGROUND

The recent introduction of virtual reality (VR) enables us to use all three dimensions in a three-dimensional (3D) image. The aim of this prospective study was to evaluate an innovative VR technique for automated 3D volume measurements of the human embryo and yolk sac in first trimester pregnancies.

METHODS

We analysed 180 3D first trimester ultrasound scans of 42 pregnancies. Scans were transferred to an I-Space VR system and visualized as 3D 'holograms' with the V-Scope volume-rendering software. A semi-automatic segmentation algorithm was used to calculate the volumes. The logarithmically transformed outcomes were analysed using repeated measurements ANOVA. Interobserver and intraobserver agreement was established by calculating intraclass correlation coefficients (ICCs).

RESULTS

Eighty-eight embryonic volumes (EVs) and 118 yolk sac volumes (YSVs) were selected and measured between 5(+5) and 12(+6) weeks of gestational age (GA). EV ranged from 14 to 29 877 mm(3) and YSV ranged from 33 to 424 mm(3). ANOVA calculations showed that when the crown-rump length (CRL) doubles, the mean EV increases 6.5-fold and when the GA doubles, the mean EV increases 500-fold (P < 0.001). Furthermore, it was found that a doubling in GA results in a 3.8-fold increase of the YSV and when the CRL doubles, the YSV increases 1.5-fold (P < 0.001). Interobserver and intraobserver agreement were both excellent with ICCs of 0.99.

CONCLUSION

We measured the human EV and YSV in early pregnancy using a VR system. This innovative technique allows us to obtain unique information about the size of the embryo using all dimensions, which may be used to differentiate between normal and abnormal human development.

Dating and growth in the first trimester

Measurement of embryonic or foetal size using the greatest length of the embryo or foetal crown rump length can be used to accurately determine the gestational age of a normal first trimester pregnancy to within three to five days. Transvaginal ultrasound scan can be used to measure the size of an embryo and gestation sac earlier than transabdominal ultrasound. The original Robinson curve used for dating pregnancies is still valid in most cases. Ultrasound dating in the first trimester is now recommended for all women with spontaneous pregnancies, even those with certain menstrual dates. First trimester growth in normal pregnancy is not uniform and is influenced by both maternal and foetal factors. Early foetal growth restriction is demonstrated in many pregnancies that subsequently end in first trimester miscarriage and is also demonstrated in fetuses with triploidy, trisomy 18 and possibly trisomy 13. Pregnancies which are small at the 11-14 week ultrasound scan appear to be at risk of later intrauterine growth restriction, preeclampsia and preterm delivery. Cross-sectional and serial measurement of foetal growth in the first trimester may be helpful in predicting both miscarriage and adverse late pregnancy outcomes.

First trimester ultrasonography in screening and detection of fetal anomalies

An obstetrical ultrasound examination provides invaluable information regarding the fetus. Until the mid-1980s, ultrasound in the first trimester was limited to localization of the pregnancy, establishing viability, and accurate dating. With the advent of high-resolution ultrasound and transvaginal scanning, a significant amount of information about the fetus can be gained and provided to the patient at a very early stage in gestation. This article provides an overview of the role of first trimester (11-13 + 6 weeks' gestation) ultrasound in screening and diagnosis of fetal anomalies. The first trimester is an ideal time for screening for aneuploidy, primarily due to the advantages that nuchal translucency (NT) measurement provides. NT measurement is also useful in establishing the risk of congenital cardiac disorders and a number of genetic and non-genetic syndromes. Significant NT thickening is associated with an increase in perinatal morbidity and mortality. Potential mechanisms resulting in increased NT are discussed. A number of new ultrasound markers for fetal aneuploidy have been investigated over the past several years, some of which appear to improve the screening efficacy of early ultrasonography. The role of these is reviewed. A number of fetal anomalies can now be consistently diagnosed in the first trimester. Their appearance at this early gestational age is discussed as well. It is clear that, data obtained by first trimester ultrasound are useful in counseling expectant parents and in planning the appropriate follow-up.

Cardiac Circumference Measurement: Possible Screening Tool in Early Pregnancy for Anomalous Cardiac Development

OBJECTIVE

In this study, cardiac circumference (CC), measured by transvaginal sonography, was analyzed to determine the growth during the early stage of pregnancy and its relationship to abdominal circumference and femur length (FL).

METHODS

Biometric measurements, including CC, were obtained in 1,182 euploid fetuses at 9-16 weeks' gestation. The CC measurements were related to gestational age (GA), abdominal circumference, and FL. The corresponding 95% confidence intervals were calculated.

RESULTS

A linear growth function was observed between CC (mm) and GA (days) (r2 = 0.601; p < 0.0001; y = 0.573 GA - 24.185). Similarly, a good correlation is described with a linear function between CC (mm) and abdominal circumference (mm) (r2 = 0.70; p < 0.0001; y = 0.343 AC + 3.696) and between CC (mm) and FL (mm) (r2 = 0.626; p < 0.0001; y = 1.335 FL + 14.444). The regression analysis that best correlates the dependent variable CC (mm) with the independent variables, GA (days), abdominal circumference (mm), and FL (mm), is: y = 0.137 GA + 0.235 AC + 0.199 FL - 3.303 (r2 = 0.708; p < 0.0001).

CONCLUSION

Our results provide normative data of the growth of the CC in early pregnancy. The good correlation described between CC and abdominal circumference and FL suggests that cardiac measurements in early pregnancy alone, or related to other fetal biometric parameters, could be used as a screening tool to identify fetuses at risk for abnormal heart development.

Fetal head-to-trunk volume ratio in chromosomally abnormal fetuses at 11 + 0 to 13 + 6 weeks of gestation

OBJECTIVE

To determine the pattern of early growth disturbance in chromosomally abnormal fetuses by comparing the volume of the fetal head to that of the trunk.

METHODS

The fetal trunk and head volume was measured using three-dimensional (3D) ultrasound in 145 chromosomally abnormal fetuses at a median gestational age of 12 (range, 11 + 0 to 13 + 6) weeks. The head volume was measured separately and then subtracted from the total head and trunk volume to obtain the volume of the fetal trunk. The head-to-trunk ratios were then calculated and the Mann-Whitney U-test was used to determine the significance of differences from 500 chromosomally normal fetuses.

RESULTS

The fetal head volume for crown-rump length (CRL) was significantly smaller than normal in trisomy 21, trisomy 13 and Turner syndrome (P < 0.001, P < 0.001 and P = 0.001, respectively), whereas no significant differences were found in trisomy 18 and triploidy (P = 0.139 and P = 0.070, respectively). The fetal trunk volume for CRL was significantly smaller in all chromosomal abnormalities (P < 0.001) except Turner syndrome (P = 0.134). The head-to-trunk ratio for CRL was significantly larger in trisomy 18, trisomy 13 and triploidy (P < 0.001), but normal in trisomy 21 (P = 0.221) and Turner syndrome (P = 0.768).

CONCLUSIONS

In trisomy 21 and Turner syndrome, the growth deficit was symmetrical with the head and trunk being equally affected, whereas in triploidy and trisomies 18 and 13 there was asymmetrical growth restriction with the trunk being more severely compromised than the head.

Alveolar capillary dysplasia in an infant with trisomy 21

We present a case of an infant with Down syndrome (trisomy 21) who was affected by alveolar capillary dysplasia and other complications including endocardial cushion defect, hypothyroidism, and intrauterine growth restriction. The patient was the product of a third pregnancy to a 33-year-old woman with no significant risk factors. The child lived for 3 months, during which he developed intractable dyspnea, hypoxemia, and cardiac dysfunction and he eventually died from septicemia and multiorgan failure. In addition to the facial phenotypic features and cardiac anomalies, the autopsy revealed the characteristic microscopic pulmonary findings of alveolar capillary dysplasia with misalignment of pulmonary veins. This appears to be the first reported case of this anomaly associated with trisomy 21. In addition to the many reasons for pulmonary hypertension that occur in children with trisomy 21, alveolar capillary dysplasia may have to be included in the differential diagnosis although it appears to be a rare association.

Fetal trunk and head volume in chromosomally abnormal fetuses at 11+0 to 13+6 weeks of gestation

OBJECTIVE

To examine the pattern of growth in chromosomally abnormal fetuses at 11+0 to 13+6 weeks of gestation and compare the trunk and head volume to crown-rump length (CRL) in defining the growth deficit in such fetuses.

METHODS

The fetal trunk and head volume was measured using three-dimensional (3D) ultrasound in 140 chromosomally abnormal fetuses at 11+0 to 13+6 (median 12) weeks of gestation, and the values were compared to 500 chromosomally normal fetuses. In each chromosomally abnormal fetus, the observed fetal trunk and head volume was subtracted from the expected mean (delta value) of the chromosomally normal fetuses of the same gestational age, and this difference was expressed as a percentage of the appropriate normal mean. The Mann-Whitney U-test was used to determine the significance of differences between the chromosomally normal and abnormal groups.

RESULTS

In trisomy 21 (n=72) and Turner syndrome (n=14) fetuses, compared to chromosomally normal fetuses, the CRL for gestation was similar (P=0.335 and P=0.317, respectively), but the fetal trunk and head volume was about 10-15% lower (P<0.001 and P=0.004, respectively). In trisomy 18 (n=29), trisomy 13 (n=14) and triploidy (n=11), the deficit in volume was about 45% (P<0.001), whereas the deficit in CRL was less than 15% (P<0.001).

CONCLUSIONS

In the quantification of the degree of early growth impairment in chromosomally abnormal fetuses, measurement of the fetal trunk and head volume using 3D ultrasound may be better than measurement of CRL.

Early transvaginal fetal orbital measurements: a screening tool for aneuploidy?

OBJECTIVE

To assess whether simple biometric parameters such as orbital diameters measured in early pregnancy by transvaginal sonography can be used as screening tools for aneuploid fetuses.

METHODS

The study group consisted of 2771 fetuses of pregnant women referred to our center for genetic amniocentesis and examined by transvaginal sonography between 11 and 16 weeks' gestation. Karyotypes were normal in 2717 fetuses, and 54 fetuses were aneuploid. Individual values for the aneuploid fetuses were compared with normative data obtained previously for single orbital measurements (interocular and binocular distance) versus gestational age and head measurements.

RESULTS

The orbital diameters were within the normal range in the cases with trisomy 21, gonosomal aberrations, trisomy 18, and unbalanced anomalies. Three of the 4 fetuses with trisomy 13 had hypotelorism, confirmed later at autopsy in 2 cases and after delivery in 1 case.

CONCLUSIONS

With regard to the small number of cases, our data suggest that ocular biometric parameters may be useful sonographic markers for trisomy 13, even if further evaluation is needed.

Uterine artery Doppler at 11-14 weeks of gestation in chromosomally abnormal fetuses

OBJECTIVE

To determine whether the major chromosomal abnormalities are associated with impaired placentation in the first trimester of pregnancy.

METHODS

This was a prospective study of 692 singleton pregnancies undergoing fetal karyotyping at 11-14 weeks of gestation. Uterine artery Doppler was carried out and the mean pulsatility index was calculated just before chorionic villus sampling.

RESULTS

The fetal karyotype was normal in 613 pregnancies and abnormal in 79, including 39 cases of trisomy 21, 11 of trisomy 18, 11 of trisomy 13, eight of Turner syndrome and 10 with other defects. There were no significant differences in the median value of uterine artery mean PI between any of the individual groups. Although in the combined group of trisomy 18, trisomy 13 and Turner syndrome fetuses, the median pulsatility index (1.60) was significantly higher than in the chromosomally normal group (median pulsatility index, 1.51; P = 0.021), in the majority of abnormal fetuses (24 of 30) mean pulsatility index was below the 95th centile of the normal group (mean pulsatility index, 2.34). There was no significant association between uterine artery mean pulsatility index and fetal nuchal translucency thickness or fetal growth deficit.

CONCLUSIONS

The high intrauterine lethality and fetal growth restriction associated with the major chromosomal abnormalities are unlikely to be the consequence of impaired placentation in the first trimester of pregnancy.

Fetal heart rate in chromosomally abnormal fetuses

OBJECTIVES

To determine the effects of chromosomal defects on fetal heart rate at 10-14 weeks of gestation.

METHODS

Fetal heart rate at 10-14 weeks of gestation in 1061 chromosomally abnormal fetuses was compared to that from 25,000 normal pregnancies. The chromosomally abnormal group included 554 cases of trisomy 21, 219 cases of trisomy 18, 95 of trisomy 13, 50 of triploidy, 115 of Turner syndrome and 28 of sex chromosome abnormalities other than Turner syndrome.

RESULTS

In the normal group, fetal heart rate decreased from a mean value of 170 beats per minute (bpm) at 35 mm of crown-rump length to 155 bpm at 84 mm crown-rump length. In trisomy 21, trisomy 13 and Turner syndrome fetal heart rate was significantly higher, in trisomy 18 and triploidy the heart rate was lower and in other sex chromosome defects it was not significantly different from normal. Fetal heart rate was above the 95th centile of the normal range in 10%, 67% and 52% of fetuses with trisomy 21, trisomy 13 and Turner syndrome, respectively. The fetal heart rate was below the 5th centile in 30% of fetuses with triploidy and 19% of those with trisomy 18.

CONCLUSIONS

Trisomy 21, trisomy 13 and Turner syndrome are associated with fetal tachycardia, whereas in trisomy 18 and triploidy there is fetal bradycardia. Inclusion of fetal heart rate in a first-trimester screening program for trisomy 21 by a combination of maternal age and fetal nuchal translucency thickness is unlikely to provide useful improvement in sensitivity.

Diagnosis and management of intrauterine growth retardation

Intrauterine growth retardation (IUGR) is associated with significant perinatal morbidity and mortality. This condition can be a sign of genetic disorders, fetal infection, uteroplacental insufficiency, or constitutionally small fetuses. Correct determination of gestational age is the first step in prenatal screening of growth-retarded fetuses. The discovery of a small-for-gestational age fetus necessitates fetal assessment for the evaluation of the etiology and prognosis, and for the determination of the optimal timing for delivery of these fetuses at risk of perinatal asphyxia. IUGR is more frequent in multiple-gestation pregnancies (23-34%) and will be discussed separately. There is no medical treatment for IUGR. Early aspirin treatment reduces the incidence of IUGR in a high-risk population but should not be used routinely in all pregnant women.

Detection of trisomy 18 by double screening in a low-risk pregnant population

OBJECTIVE

A combination of low concentrations of maternal serum alpha fetoprotein (MSAFP) and human chorionic gonadotropin (hCG) was used to screen for trisomy 18 in early 2nd-trimester pregnancies in a low-risk child-bearing population.

METHODS

Women less than 37 years of age were offered screening between 15 and 20 weeks of gestation. Those pregnancies showing low concentrations of MSAFP (<0. 75 multiples of the median) and hCG (<0.5 multiples of the mean) were considered positive. If gestational age was confirmed, genetic counselling and invasive prenatal diagnosis were offered.

RESULTS

Between January 1995 and December 1996, 19,491 women were screened, of whom 252 were found to be positive (1.25%). 145 invasive procedures were carried out, and 3 cases were detected. The odds of a fetus being affected after a positive screen result were 1 in 36.

CONCLUSIONS

Measurement of low concentrations of MSAFP and hCG in pregnant women less than 37 years of age is an effective screening test for Edward's syndrome, but with regard to the natural history of this genetic condition, it can result in overuse of invasive tests which in turn can harm chromosomally normal pregnancies. This stresses the need to evaluate these pregnancies further with detailed ultrasonographic assessment and selective fetal karyotyping only.

Chromosomally abnormal early ongoing pregnancies: correlation of ultrasound and placental histological findings

The pathophysiology of placental microscopic changes in chromosomally abnormal pregnancies remains poorly understood. We have reviewed the relationship between ultrasound findings and villous histological features in a group of 25 ongoing pregnancies presenting with fetal aneuploidy at 11 to 15 weeks of gestation. The chromosomal abnormalities were diagnosed by chorion villous sampling, and the data were compared with those of a group of 25 chromosomally normal pregnancies undergoing surgical termination and matched for gestational age. The aneuploid group included 10 pregnancies with trisomy 21, nine with trisomy 18, three with triploidy, two with monosomy X, and one with trisomy 13. The overall degree of agreement between the two investigators for the histological diagnosis was good (kappa, 0.64), and the sensitivity of histology ranged between 72.0% and 80.0%. Fetal and placental edema was observed on scan in 10 and 7 cases, respectively, of the aneuploid group and was systematically associated with trophoblastic hypoplasia, stromal edema, or cavitation, reduced vascularization, and ramification of the main villous trunks. Fetoplacental hydrops was not observed in the euploid group. These findings indicate that histological changes observed in the placenta of fetuses from ongoing pregnancies presenting with aneuploidy can be linked with early fetal hydrops. The villous features in these cases are probably secondary to a reduction in the villous circulation due to a cardiovascular defect and leading to generalized stromal edema. The reduced villous branching and trophoblastic hypoplasia could be secondary to the enlargement of all villous types or to a basic defect in placental development.

Antenatal screening for aneuploidy

There are several methods of antenatal screening for aneuploidy. Most are aimed at the identification of women at increased risk of Down syndrome, the most common abnormal karyotype conferring a significant risk of serious long-term morbidity. Traditional maternal-age-based screening has largely been replaced by programmes based on biochemical markers in maternal serum in the second trimester of pregnancy. However, in recent years there has been a considerable drive towards earlier screening such that there are now a range of potential programmes based on various combinations of maternal age, serum markers and ultrasound findings. There is currently much debate as to which are the most effective methods of screening for aneuploidy.