Diagnosis of fetal defects in twin pregnancies at routine 11–13‐week ultrasound examination

Abstract

Objectives To examine the performance of the routine 11–13‐week scan in detecting fetal defects in twin pregnancies and to examine if, in pregnancies with a fetal defect, compared to those with normal fetuses, there is increased incidence of nuchal translucency thickness (NT) ≥ 95th and ≥ 99th percentiles or intertwin discordance in crown–rump length (CRL) ≥ 10% and ≥ 15%. Methods This was a retrospective analysis of prospectively collected data in twin pregnancies undergoing routine ultrasound examination for fetal anatomy, according to standardized protocols, at 11–13 weeks' gestation between 2002 and 2019. Pregnancies with known chromosomal abnormality were excluded. The final diagnosis of fetal defect was based on the results of postnatal examination in cases of live birth and on the findings of the last ultrasound examination in cases of pregnancy termination, miscarriage or stillbirth. The performance of the 11–13‐week scan in the detection of fetal defects was determined. Results The study population of 6366 twin pregnancies with two live fetuses at 11–13 weeks' gestation included 4979 (78.2%) dichorionic (DC) and 1387 (21.8%) monochorionic (MC) twin pregnancies. The main findings were: first, the overall incidence of fetal defects was higher in MC than in DC twins (2.8% vs 1.3%); second, the proportion of defects diagnosed in the first trimester was higher in MC than in DC twins (52.6% vs 27.1%); third, the pattern of defects in relation to detectability at the 11–13‐week scan (always detectable, sometimes detectable and never detectable) was similar to that reported previously in singleton pregnancies; fourth, always‐detectable defects included acrania, alobar holoprosencephaly, encephalocele, pentalogy of Cantrell, exomphalos, body‐stalk anomaly, twin reversed arterial perfusion sequence and conjoined twins; fifth, the incidence of fetal NT ≥ 95th percentile was higher in those with than in those without a defect (16.5% vs 4.5% in DC twins and 19.2% vs 5.9% in MC twins) and this was also true for NT ≥ 99th percentile (8.3% vs 1.0% in DC twins and 15.4% vs 2.0% in MC twins); and sixth, the incidence of CRL discordance ≥ 10% was higher in those with than in those without a defect (20.2% vs 7.9% in DC twins and 33.8% vs 9.3% in MC twins) and this was also true for CRL discordance ≥ 15% (10.1% vs 1.9% in DC twins and 28.2% vs 2.8% in MC twins). Conclusions First, fetal defects are more common in MC than in DC twin pregnancies. Second, first‐trimester detection of fetal defects in DC twin pregnancies is similar to that in singleton pregnancies. Third, first‐trimester detectability of defects in MC twins is higher than in DC twins. Fourth, in twin pregnancies with a fetal defect, there is higher intertwin discordance in CRL and incidence of increased NT, but the predictive performance of screening by these markers is poor. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Outcome of twin pregnancy with two live fetuses at 11–13 weeks' gestation

“…Endoscopic laser ablation of intertwin communicating placental vessels was carried out in 127 (10.0%) MCDA twin pregnancies at a median gestational age of 18 (range, [16][17][18][19][20][21][22][23][24][25][26][27] weeks. The indications for intervention were TTTS Stage IV (n = 1), Stage III (n = 54), Stage II (n = 11) and Stage I (n = 5), sFGR Type II (n = 25) and Type III (n = 3), sFGR Type II and TTTS Stage III (n = 19), sFGR…”

“…This study constitutes a retrospective analysis of data derived from a routine clinical service and did not require ethics committee approval. The same database used in this study was also used in our previous publications on the relationship of increased discordance in crown-rump length and increased nuchal translucency thickness with pregnancy outcome 20,21 , first-trimester diagnosis of non-chromosomal fetal abnormalities 22 and the effect of one fetal death on pregnancy outcome 23 .…”

Intertwin discordance in fetal size at 11–13 weeks' gestation and pregnancy outcome

“…We excluded pregnancies with chromosomal abnormality or a major defect diagnosed prenatally or postnatally and those with twin reversed arterial perfusion sequence. The same database used in this study was also used in our previous publications on the outcome of MC and DC twins, the relationship between increased nuchal translucency thickness and pregnancy outcome, first‐trimester diagnosis of non‐chromosomal fetal abnormalities and the effect of one fetal death on pregnancy outcome.…”

Monochorionic diamniotic twins: What do I tell the prospective parents?

“…6,7 Moreover, 65% of spontaneous monozygotic twins are monochorionic and 35% dichorionic, whereas monozygotic twins after fertility treatment are more likely to have a monochorionic placenta (80%) with only 20% being dichorionic. 7,8 So even with a single embryo transfer, the chance of conceiving a monozygotic and mostly monochorionic twin is around 1.5% to 2%, 6,7,9 and their survival is probably lower than that of spontaneously conceived MCDA twins. 10 Apart from fertility treatment, there are no other known risk factors.…”

“…We also label the twins according to their position and cord insertion in the placenta. 12,13 Because MCDA twins have an increased risk of anomalies, of which 50% can be detected in the first trimester, 8 we perform a thorough anatomic survey. We also offer to screen for chromosomal anomalies.…”