Prenatal diagnosis for multiple pregnancies

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Abstract
In multiple pregnancies, first trimester ultrasound is crucial to diagnose chorionicity, to detect major structural defects, and to screen for chromosomal abnormalities based on nuchal translucency measurement. The efficacy of nuchal translucency measurement screening in twins might be improved when combined with first trimester maternal serum screening. In twins as in singletons, the risk of fetal loss attendant to chorionic villi sampling and to amniocentesis are similar. When an invasive procedure is indicated in twins, chorionic villi sampling has, over amniocentesis, the advantage of allowing selective termination to be performed in the first trimester, when the procedure related risk of miscarriage is minimal. It has the disadvantage of leading to ambiguous results in up to 2% of cases. While chorionic villi sampling is the choice technique in pregnancies at very high risk, amniocentesis is still indicated in cases at more moderate risk. In monochorionic pregnancies, selective termination can now be performed using a variety of techniques including bipolar or monopolar cord coagulation, and, in acardiac twins, alcohol ablation. However, selective termination remains more hazardous in monochorionic than in dichorionic pregnancies. The outcome of the twin-to-twin transfusion syndrome has been substantially improved by laser photocoagulation of placental shunts and by amniodrainage, but randomized trials are needed to establish the optimal therapeutic strategy, and further pathophysiologic research might result in new treatments.

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