Prediction of chorionicity in twin pregnancies at 10-14 weeks of gestation

Objective To examine the accuracy of sonographic determination of chorionicity in twin pregnancies at 10–14 weeks of gestation.
Design Prospective study on the sonographic prediction of chorionicity at 10–14 weeks of gestation.
Participants During a 30 month period, from October 1997 to May 2000, 165 women attending the departments of fetal medicine or ultrasound.
Methods Sonographic criteria used in the diagnosis of chorionicity were the number of placental sites, the lambda (λ) and T signs and the thickness of the inter-twin membrane. The diagnosis of chorionicity was made at the time of the ultrasound examination using all these features and subsequently compared with the postnatal diagnosis, confirmed either by placental histology or discordancy in infant sex.
Results In 150 cases with confirmation of chorionicity following delivery, 116 were postnatally classified as dichorionic and 34 monochorionic. Prenatal ultrasound examination correctly identified chorionicity in 149 (99.3%) cases. The most reliable indicator for dichorionicity was a combination using the λ sign or two separate placentae with a sensitivity and specificity of 97.4% and 100%, respectively. The most useful test in predicting monochorionicity was the T sign with a sensitivity of 100% and specificity of 98.2%. Measurement of the inter-twin membrane thickness was a less reliable indicator where the sensitivity for dichorionicity and specificity for monochorionicity was only 92.6%.
Conclusions Ultrasound examination of twin pregnancies at 10–14 weeks of gestation predicts chorionicity with a high degree of accuracy using a combination of the number of placentae, λ and T signs and inter-twin membrane thickness. All hospitals should encourage departments providing ultrasound services to undertake chorionicity determination when examining women with twin pregnancies at this gestation.     

The prevalence and consequences of missed abortion in twin pregnancies at 10 to 14 weeks of gestation

In singleton pregnancies at 10 to 14 weeks of gestation the prevalence of missed abortion is about 2%. In an ultrasound screening study at 10 to 14 weeks of gestation involving 492 twin pregnancies the prevalence of missed abortion was about twice as high as in singletons. The risk of subsequent miscarriage in twin pregnancies with one missed abortion was about ten times higher than in normal twin pregnancies. These findings may have important implications both in terms of counselling and for future research into the causes of miscarriage.     

Histomorphological features of chorionic villi at 10-14 weeks of gestation in trisomic and chromosomally normal pregnancies

This study examines histomorphometric features in chorionic villi obtained by chorionic villus sampling (CVS) at 11-14 weeks of gestation from 124 ongoing pregnancies (38 with trisomy 21, 14 with trisomy 18, 11 with trisomy 13 and 61 chromosomally normal controls). In the trisomy 21 group there was an inverse relationship between fetal nuchal translucency thickness (NT) and villus diameter and number of capillaries per villus cross-section. In about half of the cases there was perivillous fibrinoid present, and the amount of this increased with gestation. Compared to the chromosomally normal group, in trisomy 18 the villus diameter was smaller and the number of capillaries per villus cross-section was reduced. In the trisomy 21 group, villi had an increased percentage of two layered trophoblast present and an increased proportion of villus capillaries with nucleated red blood cells present. In all three trisomies, but particularly in trisomies 18 and 13, both the amount of basophilic stippling of the basement membrane and the proportion of cases with stippling was increased. These results provide data on the possible mechanisms of increased fetal NT and on abnormal placental development in fetal trisomies.     

Maternal serum alpha-fetoprotein in fetal neural tube and abdominal wall defects at 10 to 14 weeks of gestation

Maternal serum alpha-fetoprotein concentration was determined in nine pregnancies with fetal anencephaly, seven with exomphalos containing liver, two with spina bifida and 100 normal controls at 10 to 14 weeks of gestation. The median alpha-fetoprotein in the group with fetal anencephaly and exomphalos was significantly higher than in normal fetuses but the sensitivity of this test is likely to be only about 30% for a false positive rate of 5%.     

Maternal serum activin A and inhibin A in trisomy 18 pregnancies at 10-14 weeks

In 45 cases of trisomy 18 and 493 control pregnancies at 10-14 weeks of gestation, maternal serum inhibin A, total activin A, free beta-hCG and PAPP-A were measured. In the trisomy 18 pregnancies the median values were 0.74 MoM for inhibin A, 1.23 MoM for activin A, 0.38 MoM for free beta-hCG and 0.16 MoM for PAPP-A. The degree of deviation from normal in the levels of inhibin and activin is small in comparison with free beta-hCG and PAPP-A and they are therefore unlikely to be of value in improving the sensitivity of 90% for a 1% false-positive rate achieved by screening with fetal nuchal translucency and maternal serum free beta-hCG and PAPP-A.     

Diamniotic twin pregnancies with a single placental mass; prediction of chorionicity at 11 to 14 weeks of gestation

OBJECTIVE: To assess the accuracy of transvaginal ultrasound (US) in the prediction of the chorionicity of diamniotic twin pregnancies with a single placental mass at 11 to 14 weeks of gestation. METHOD: From June 2006 to April 2007, we determined chorionicities by depiction of the amnion and chorion at the membrane-to-placental interface using transvaginal US. Pregnancies were classified as monochorionic when two layers of the amnion were identified as dichorionic when either one layer of the chorion and two layers of the amnion or one layer of the chorion and one layer of the amnion were seen. RESULTS: In 65 out of 70 (92.9%) diamniotic twin pregnancies with a single placental mass, we were able to determine the chorionicity by depiction of the amnion and chorion at the membrane-to-placental interface using transvaginal US. The predictive accuracy was 100% (95% confidence interval: 92-100%) for 52 twin pregnancies considered to be dichorionic by transvaginal US and 100% (95% CI: 73-100%) for 13 twin pregnancies considered to be monochorionic. CONCLUSION: The chorionicity of diamniotic twin pregnancies with a single placental mass can be reliably predicted by transvaginal US depiction of the amnion and chorion at 11 to 14 weeks of gestation.     

Screening for trisomy 21 in twin pregnancies by maternal age and fetal nuchal translucency thickness at 10–14 weeks of gestation

Objective To determine the prevalence of increased fetal nuchal translucency thickness in twin pregnancies and to evaluate screening for trisomy 21 by a combination of translucency thickness and maternal age.
Design Prospective screening study at 10 to 14 weeks of gestation.
Setting Fetal Medicine Centre.
Population 22,518 self-selected pregnant women at 10 to 14 weeks of gestation, including 21,477 singleton and 448 twin pregnancies with live fetuses.
Methods Fetal nuchal translucency thickness was measured by ultrasound examination at 10–14 weeks. Sensitivity and false positive rates of screening for trisomy 21 by a combination of fetal nuchal translucency thickness and maternal age were calculated.
Main outcome measures Prevalence of increased nuchal translucency thickness and detection of trisomy 21.
Results In the 448 twin pregnancies the nuchal translucency thickness was above the 95th centile of the normal range (for crown-rump length in singletons) in 65/896 fetuses (7.3%), including 7/8 (88%) with trisomy 21. Increased translucency was also present in four fetuses with other chromosomal abnormalities. In the chromosomally normal twin prebmancies the prevalence of increased nuchal translucency was higher in fetuses from monochorionic (8.4%; 16/190) than in those with dichori-onic pregnancies (5.4%; 37/688). The minimum estimated risk for trisomy 21, based on maternal age and fetal nuchal translucency thickness, was 1 in 300 in 19.5% (175/896) of the twins including all eight of those with trisomy 21.
Conclusions In twin pregnancies the sensitivity of fetal nuchal translucency thickness in screening for trisomy 21 is similar to that in singleton pregnancies, but the specificity is lower because translucency is also increased in chromosomally normal monochorionic twin pregnancies.     

Raised maternal serum inhibin A concentration at 10 to 14 weeks of gestation is associated with pre-eclampsia

Maternal serum inhibin A and free β human chorionic gonadotrophin (β-hCG) were measured in 759 chromosomally normal, pregnant women at 10–14 weeks of gestation. There were nine who subsequently developed pre-eclampsia and in these women the maternal serum inhibin A concentration was significantly higher than in the normotensive controls.     

Maternal midtrimester serum AFP and free beta-hCG levels in in vitro fertilization twin pregnancies

We aimed to compare the levels of alpha-fetoprotein (AFP) and free beta-human chorionic gonadotrophin (beta-hCG) levels as multiples of the median (MoM) values between spontaneous and in vitro fertilized (IVF) twin pregnancies. The control group of spontaneous singleton pregnancies was used for calculating the gestational age specific median levels of the values. Within a cohort of 19 310 pregnancies, 145 twin pregnancies were identified. The data were collected from Down syndrome (DS) screening programmes in four University catchment areas in Finland between 1994-98. Maternal midtrimester serum marker levels were measured across gestational weeks 14-18. There were no fetal chromosome anomalies in either of the twin groups or the singleton group. Serum AFP of 145 and beta-hCG values of 39 spontaneous twin pregnancies were compared to the values of 6548 singleton pregnancies. In IVF twins 30 AFP and 29 beta-hCG values were compared to the levels of the control group. Both AFP and beta-hCG values were twice as high in the spontaneous twin pregnancies (medians 2.18 and 1.83 MoM respectively) as in the singleton group (medians 1.00 and 1.00 MoM respectively). In IVF twin pregnancies beta-hCG levels were higher (median 2.20 MoM) than in spontaneous twins (p=0.08), whereas no significant difference was found in AFP levels (2.30 MoM). In conclusion, the higher levels of beta-hCG levels in IVF twin pregnancies should be considered in DS screening to avoid high false positive rates.     

Screening for triploidy by fetal nuchal translucency and maternal serum free beta-hCG and PAPP-A at 10-14 weeks of gestation

In 25 cases of triploidy at 10-14 weeks of gestation, compared with 947 controls, the median multiple of the median (MoM) fetal nuchal translucency (NT) thickness was significantly increased (1.89 MoM), and maternal serum total and free beta-human chorionic gonadotrophin (hCG) were increased (3.13 MoM and 4.59 MoM respectively), alpha fetoprotein (AFP) was increased (2.14 MoM), and pregnancy associated plasma protein A (PAPP-A) was decreased (0.12 MoM). There are two types of triploidy. In type I, where the additional chromosome set is of paternal origin, the placenta is partially molar and the fetus is relatively well-grown. Type II, where the extra chromosome set is of maternal origin, is characterized by a small normal looking placenta and severe asymmetrical fetal growth restriction. In type I triploidy there was increased fetal NT (2.76 MoM), maternal serum total hCG (4.91 MoM), free beta-hCG (8.04 MoM), and AFP (3.22 MoM), and mildly decreased PAPP-A (0.75 MoM). In type II triploidy fetal NT was not increased (0.88 MoM), and there was a decrease in maternal serum total hCG (0.16 MoM), free beta-hCG (0.18 MoM), PAPP-A (0.06 MoM) and AFP (0.77 MoM). We conclude that a large proportion of triploidy cases of both phenotypes could be identified in the first trimester using NT, maternal serum free beta-hCG and PAPP-A with a combination of trisomy 21 risk and an atypicality approach.     

Maternal serum free beta-hCG levels in uncomplicated pregnancies at the 10th-15th week of gestation and the development of obstetric complications

OBJECTIVE: To determine if free beta-human chorionic gonadotropin (hCG) serum levels at the 10th-14th week of gestation were different in groups of women who had experienced pregnancy complications. STUDY DESIGN: The obstetric records of women who had uncomplicated pregnancies when they consented to donate blood for biochemical research purposes early in pregnancy were reviewed. Two hundred thirteen of these women had donated blood at the 10th-14th week of gestation. Of these, 135 had uneventful pregnancies and delivered at term, 19 delivered before 37 weeks'gestation, 10 had fetuses small for gestational age, 4 developed pregnancy-induced hypertension, 7 developed gestational diabetes, 10 aborted spontaneously, 4 had an intrauterine fetal death after 20 weeks' gestation, and 24 were lost to follow-up. After the clinical groups had been identified, the 213 maternal serum stored samples were thawed and free beta-hCG measured by enzyme-linked immunosorbent assay. After normalization of the data, ANOVA was used to compare mean gestational age and mean free beta-hCG levels within groups. RESULTS: The overall mean gestational age at maternal blood sampling was 12.5 weeks. All groups had similar gestational ages at blood sampling (P = .18). The overall mean free beta-hCG serum level was 18.05 mIU/mL. Only the group of women who went on to experience spontaneous abortions had significantly lower free beta-hCG lev- els (mean, 10.45 mIU/mL; P < .03) CONCLUSION: Our data suggest that of the groups with obstetric complications evaluated, only the group of women who experienced spontaneous abortions had significantly different serum levels of free beta-hCG at the 10th-14th week of gestation.