TY - CHAP M1 - Book, Section TI - Monoamniotic Twins A1 - Bianchi, Diana W. A1 - Crombleholme, Timothy M. A1 - D'Alton, Mary E. A1 - Malone, Fergal D. PY - 2015 T2 - Fetology: Diagnosis and Management of the Fetal Patient, 2e AB - Key PointsMonoamniotic twinning is a rare form of twinning where both twins occupy a single amniotic sac.This form of twinning occurs when a single embryo splits during postovulation days 8 to 10.The most common way to diagnose monoamniotic twins antenatally is failure to visualize a dividing membrane in the presence of a single placental mass and like-gender twins. During the first trimester, the presence of two embryos in a single sac, but with only one yolk sac, is highly suggestive of monoamnionicity.These pregnancies are at risk for significant perinatal morbidity and mortality. This has been attributed to preterm delivery, intrauterine growth restriction, congenital anomalies, vascular anastomoses between twins, and umbilical cord entanglement or cord accidents.Intense antenatal surveillance and timed delivery has been shown to improve outcomes. This typically takes the form of elective hospitalization with daily nonstress testing at 24 to 26 weeks’ gestation, and increased frequency of testing if variable decelerations are noted.Elective delivery at 32 to 34 weeks’ gestation is recommended if fetal testing remains reassuring and cesarean delivery is most commonly recommended. SN - PB - McGraw-Hill Education CY - New York, NY Y2 - 2024/04/19 UR - obgyn.mhmedical.com/content.aspx?aid=1106401476 ER -