Ultrasound management of twin pregnancies

The rate of multiple pregnancies is showing a significant increase all over the world. Twin gestations are considered as high-risk condition because they are responsible for the increase of perinatal morbidity and mortality.
The monitoring of twin pregnancies is mainly based on ultrasound. Usually, ultrasound monitoring is based on chorionicity. Thus, every attempt should be made to determine and report amnionicity and chorionicity when a twin pregnancy is identified. Dating should be done with first trimester ultrasound.
Beyond the first trimester, a combination of parameters rather than a single parameter should be used to confirm gestational age. However, to avoid missing a situation of early intrauterine growth restriction in one twin, in our unit we consider dating pregnancy using the larger fetus.
In twin pregnancies, aneuploidy screening using nuchal transluscency measurements should be offered. Detailed ultrasound examination to screen for fetal anomalies should be offered, preferably between 18 and 22 weeks' gestation, in all twin pregnancies. When ultrasound is used to screen for preterm birth in a twin gestation, endovaginal ultrasound measurement of the cervical length should be monthly performed.
Singleton growth curves currently provide the best predictors of adverse outcome in twins and may be used for evaluating growth abnormalities. Increased fetal surveillance should be considered when there is either growth restriction diagnosed in one twin or significant growth discordance. Umbilical artery Doppler  is routinely offered in complicated twin pregnancies.
For defining oligohydramnios and polyhydramnios, the deepest vertical pocket in either sac is used.
More frequent examinations are required in case of monochorionic pregnancies. Thus, a detailed ultrasound exam should be performed every two weeks to exclude any markers of specific complications (TTTS, TAPS…) including the measurement of the systolic blood flow in the MCA.

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