Twin pregnancies.

Abstract

Twin pregnancies, resulting in 2-3\u200a% of all deliveries, are high risk pregnancies which need specialized care. A correct dating of pregnancy and the assessment of the chorionicity/amnionicity in the first trimester (<\u200a=\u200a13\u200a+\u200a6 gestational weeks, GW) is essential for further monitoring. During first trimester risk stratification of monochorionic pregnancies includes evaluation of discordance of crown-rump-lengths, nuchal translucencies and amniotic fluid. At 16 GW sonographic risk evaluation of monochorionic twins involves differences in amniotic fluid and abdominal circumferences and detection of a velamentous cord insertion. A screening for fetal malformations with cervical length measurement as screening for preterm birth (cut-off <\u200a25\u200amm) should be offered all twin pregnancies around 20 GW. In uncomplicated dichorionic pregnancies US examination should be performed every 4 weeks onwards to check fetal growth and amniotic fluid. An intertwin weight discordance >\u200a20\u200a% identifies pregnancies at increased risk of adverse outcome. Monochorionic pregnancies should be followed at least every two weeks for screening of twin-twin transfusion syndrome (TTTS), twin-anemia-polycythemia-sequence (TAPS) and selective fetal growth retardation (sFGR) with a start at 16 GW. The type 1-3 classification of sFGR in monochorionic twins depends on the pattern of end-diastolic velocity at the umbilical artery Doppler. The diagnosis of TTTS requires the presence of an oligyohydramnios (deepest vertical pocket (DVP) <\u200a2\u200acm) in the donor twin and a polyhydramnios (DVP >\u200a8\u200acm) in the recipient twin. However, the diagnosis of TAPS is based on the finding of discordant MCA Doppler values with a delta-MCA PV >\u200a0.5\u200aMoM.