Twin pregnancies are followed more closely than singleton pregnancies due to higher risk for complications such as twin-twin transfusion syndrome, selective fetal growth restriction, and preterm labor. Ultrasound is a non-invasive and highly useful tool for screening, diagnosis, and guiding management of these potential complications. Ultrasound monitoring protocols vary between different types of twin pregnancies.
Image by Kevin Dufendach, MD (2008). Used by permission. CC BY 3.0
Lambda or Delta Sign Indicating Dichorionic Twins
T Sign Indicating Monochorionic Twins
Uncomplicated monochorionic twin pregnancy (see SMFM checklist in ‘Learn More – Primary Sources’ below)
Note: ISUOG guidelines do include umbilical artery Doppler monitoring as part of routine surveillance | ACOG/ SMFM considers evidence to be unclear for uncomplicate monochorionic twins
Uncomplicated dichorionic twin pregnancy
Most twin pregnancies will have good outcomes. However, diligence is required, especially in the case of monochorionic twins due to risk for twin-twin transfusion syndrome (TTTS) and twin anemia polycythemia sequence (TAPS). Monochorionic twins may have potentially significant vascular anastomoses such that the twins share a common vasculature. Significant risks for dichorionic twins include preterm labor, medical complications due to increased placental mass (e.g., preeclampsia and GDM) and selective growth restriction. Different centers will have different protocols for labeling twin A vs twin B. The important point is to be consistent with labeling.
ACOG/ SMFM Practice Bulletin 231: Multifetal Gestations: Twin, Triplet, and Higher-Order Multifetal Pregnancies
SMFM Special Statement: Updated checklists for management of monochorionic twin pregnancy
ISUOG Practice Guidelines: role of ultrasound in twin pregnancy
ACOG SMFM Committee Opinion 831: Medically Indicated Late-Preterm and Early-Term Deliveries
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