Antenatal assessment of twin gestation

We have identified that twin gestation presents considerable risks to the well-being of both infants that can be traced to either related maternal or intrinsic fetoplacental factors. A protocol for the assessment of twin gestation is established, beginning with a basis in ultrasound identification of twinning and correct gestational dating. Because most hazards for twins are related to abnormal growth, discrepant growth between twins, and abnormalities of placentation, the approach to assessing well-being requires good serial biometry of twins. This critical review addresses the individual and combined application of standard tests used for evaluation of intrauterine health in single pregnancies: (1) ultrasound fetal growth curves; (2) Doppler velocimetry of the umbilical artery; (3) nonstress tests; (4) amniotic fluid assessment and (5) biophysical profile testing. The best current evidence suggests that there are clear deficiencies in the basis for growth nomograms for twin gestations, and with the exception of femur length, most individual anatomic measurements start to deviate from singleton standards between 21 and 30 weeks' gestation. Regardless of formulae used, estimated fetal weight provides the best discriminator for discordant growth. Dynamic assessment of fetal well-being is best provided by a combination of Doppler velocimetry and nonstress testing. Semiquantitative amniotic fluid assessment, other than establishing pathological conditions (eg, twin transfusion syndrome), is problematic and difficult to reproduce. Inadequate data exist to establish the value of the biophysical profile in twins. Given the limitations of present knowledge, serial assessment of twins beginning in the midtrimester with ultrasound observation, and adding combinations of Doppler velocimetry and nonstress testing in the third trimester, seems to represent the most reasonable current clinical approach to twin well-being.