[First trimester ultrasound screening for structural and chromosomal anomalies in multiple pregnancy]

To assess the feasibility of first trimester ultrasound screening for structural and chromosomal fetal anomalies in multiple gestations.

An observational prospective follow up study was carried out in 32 cases of multiple pregnancies. Two scans were scheduled in each case--the first, between 6-9 weeks of gestation (w.g.) and the second, between 11-14 w.g. The aim was assessment of fetal number, viability, chorionicity/amnionicity and fetal biometry. In addition, nuchal translucency [NT] measurement, assessment of risk for chromosomal anomalies and fetal anatomy survey were always performed. Increased NT > or = 95 percentile and/or detection of structural anomaly were considered indications for invasive prenatal diagnosis and fetal karyotyping. Selective fetocide was considered in cases of chromosomal or structural anomalies and in high-order multiple gestations (> or = 3 fetuses). Pregnancy outcome was ascertained by the physical examination of the fetuses, placentas and membranes postpartum, the hospital records, the referring physicians or the parents.

From 32 cases of multiple pregnancies included in the study, 28 were twins, and 4--triplets. 68% (19/28) of the twin pregnancies were bichorionic-biamniotic [Bi-Bi], 25% (7/28)--monochorionic-biamniotic [Mo-Bi] and 7% (2/28)--monochorionic-monoamniotic [Mo-Mo]. 4 cases of increased NT in one of the twins (1--associated with trisomy 21) were observed, as well as 2 cases of structural fetal anomalies (1--discordant for exencephaly, and 1--with conjoint twins), 2 cases of feto-fetal transfusion syndrome that developed in the second trimester (1--associated with increased NT between 11-14 w.g.), 1 case of TRAP syndrome [twin-reversed arterial perfusion] and 1 case of cord entanglement in monoamniotic twins. In addition, there were 4 cases of a vanishing twin in the first trimester, and in 2 other cases spontaneous miscarriage of both twins occurred before 24 w.g. In two of the triplet pregnancies selective fetocide was performed, one was successfully delivered at 33 w.g. and in the last case the parents chose to terminate the pregnancy.

First trimester ultrasound is a method of choice for detection of major structural fetal anomalies in multiple gestations. Increased NT between 11-14 w.g. in multiple pregnancies is a useful screening tool for detection of chromosomal fetal anomalies, while in monochorionic twins its presence might predict the development of fetofetal transfusion syndrome. First trimester selective fetocide in high-order multiple gestations or in affected twins is one of the options in pregnancy management.