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Placental Cord Insertion and Birth Weight Discordancy in Twin Gestations

Hanley, Maryellen L. MD, MPH; Ananth, Cande V. PhD, MPH; Shen-Schwarz, Susan MD; Smulian, John C. MD, MPH; Lai, Yu-Ling RNC, MSN; Vintzileos, Anthony M. MD

Original Research

OBJECTIVE To evaluate whether abnormal umbilical cord insertion (UCI) into the placenta is a risk factor for birth weight discordancy in twin gestations.

METHODS Pathology records of all liveborn twins delivered between January 1993 and June 1996 were reviewed. The information collected included gestational age at delivery, birth weight, gross placental pathology, and placental UCI—velamentous, marginal, or disc. Discordancy in birth weight was defined as an intrapair difference of at least 20%. Analyses were stratified on placental chorionicity. Odds ratios and 95% confidence intervals for birth weight discordancy were calculated based on the presence of an abnormal (velamentous or marginal) placental UCI relative to normal (disc) UCI on both placentae, after adjusting for potential confounders.

RESULTS There were 447 twin pairs identified. Dichorionic diamniotic placentation was present in 358 pairs (80.1%), monochorionic diamniotic in 84 (18.8%), and monochorionic monoamniotic in five (1.1%). There was a 13-fold increase in the risk of birth weight discordancy in monochorionic diamniotic twins in the presence of a velamentous UCI (odds ratio 13.5, 95% confidence interval 1.4, 138.4), with a rate of birth weight discordancy of 46%. This relationship was not demonstrated in dichorionic diamniotic twins (odds ratio 1.0, 95% confidence interval 0.3, 3.5).

CONCLUSION Birth weight discordancy in twins is a different entity depending on chorionicity. The substantial increase in birth weight discordancy in monochorionic diamniotic twins that accompanies velamentous UCI underscores the need for prenatal detection and increased surveillance in these twins.

Nearly half of monochorionic diamniotic twins with velamentous cord insertions demonstrate birth weight discordancy; therefore, efforts to identify such pregnancies prenatally may facilitate management.

Division of Maternal-Fetal Medicine, and Section of Epidemiology and Biostatistics, Department of Obstetrics, Gynecology, and Reproductive Sciences, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, St. Peter's University Hospital, and Department of Pathology, St. Peter's University Hospital, New Brunswick, New Jersey.

Reprints are not available. Address correspondence to: Maryellen L. Hanley, MD, MPH, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, St. Peter's University Hospital, 254 Easton Avenue, MOB-4th Floor, New Brunswick, NJ 08903–0591; E-mail:

Received June 20, 2001. Received in revised form October 15, 2001. Accepted October 25, 2001.

© 2002 The American College of Obstetricians and Gynecologists