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Does Sonographic Determination of Placental Location Predict Fetal Birth Weight in Diamniotic-Dichorionic Twins?

Division of Maternal-Fetal Medicine, Department of Obstetrics, Gynecology, and Reproductive Sciences (V.B., K.A.E., J.L.S.), and Department of Community and Preventive Medicine (S.M.E., L.F.), Mount Sinai School of Medicine and Medical Center, New York, New York USA.

Address correspondence to Victoria Belogolovkin, MD, Division of Maternal-Fetal Medicine, Department of Obstetrics, Gynecology, and Reproductive Sciences, Mount Sinai Medical Center, 5 E 98 St, Second Floor, Box 1171, New York, NY 10029-6574 USA. E-mail: victoria.belogolovkin{at}mssm.edu

Objective. The purpose of this study was to determine the association between placental location in diamniotic-dichorionic twins as determined at the time of anatomic survey and birth weight. Methods. We retrospectively identified all diamniotic-dichorionic twins in our Maternal-Fetal Medicine sonography database between 2000 and 2005 who had an anatomic survey, went on to be delivered at our hospital, and had records available for review (n = 304). Placental location for each twin was determined at the time of anatomic survey and grouped into both anterior or both posterior versus separate anterior and posterior. Maternal and fetal characteristics were collected from chart review. Placental pathologic findings were available for 249 (83%) patients. Outcomes analyzed were percent discordance, small size for gestational age of twin A or B, and difference in birth weight as a continuous variable. Multivariable logistic regression using stepwise backward elimination was used to adjust for potential confounders. Results. There was no difference in discordance of 20% or greater or incidence of small size for gestational age when both placentas were both anterior and both posterior compared with separate anterior and posterior: adjusted odds ratio (AdjOR), 1.38 (95% confidence interval [CI], 0.64–2.95); and AdjOR, 1.29 (95% CI, 0.57–2.89). The actual birth weight difference (A – B) was not affected by placental location (P = .36). Opposite sex fetuses and nulliparity were significantly associated with birth weight discordance: AdjOR, 2.68 (95% CI, 1.39–5.17); and AdjOR, 0.34 (95% CI, 0.28–0.94). Conclusions. We did not find a correlation between birth weight and placental location in our cohort analysis. The presence of sex-discordant twins was associated with birth weight discordance of 20% or greater, whereas nulliparity was protective.

Key Words: birth weight • diamniotic-dichorionic twins • placental location

Abbreviations: A-A, both anterior • A-P, separate anterior and posterior • IUGR, intrauterine growth restriction • IVF, in vitro fertilization • MPR, multifetal pregnancy reduction • P-P, both posterior • SGA, small for gestational age