Relationship of twin zygosity and risk of preeclampsia

OBJECTIVE: Twin gestations are known to be at higher risk for preeclampsia. One theory suggests that maternal recognition of fetal and trophoblastic t issues as foreign may be a factor. If that hypothesis Is true, mothers carr ying monozygous (MZ) gestations (ie a single fetal graft) might be predicte d to have a lower rate of preeclampsia than those carrying dizygous; (DZ) g estations. To evaluate this hypothesis, we compared the rate of preeclampsi a in mothers with MZ and DZ twin gestations. STUDY DESIGN: Seven hundred sixty-eight twin deliveries from 1994 to 1999 w ere reviewed. Placental pathology reports were reviewed to determine the ch orionic state of each placenta. Monochorionic placentas were assumed to be MZ. Dichorionic placentas were categorized as DZ if the neonates were of di fferent sexes or different blood types. Maternal and fetal data were abstra cted from the medical records. Preeclampsia was defined by standard criteri a of the National Institutes of Health Working Group on High Blood Pressure . Our analysis was limited to women with pregnancies reaching at least 30 w eeks of gestation where zygosity could be determined. RESULTS: Our analysis included 464 twin pregnancies, 154 MZ and 310 DZ. Amo ng nulliparous. women, the rate of preeclampsia was 16% (25/170) for DZ twi ns versus 20% (15/75) for MZ twins (P = .3). Among multiparous women, the r ate was 8% (11/140) for DZ twins and 5% (4/79) for MZ twins (P = .4). In a logistic regression performed to control for confounding by maternal age, g estational age at delivery, assisted reproduction, and male sex, dizygotic state was associated with an odds ratio of 1.4 (95% CI = 0.5-3.9) for devel oping preeclampsia in nulliparous women and 1.2 in multiparous women (95% C I = 0.3-5.0). CONCLUSIONS: These results do not support the hypothesis that zygosity affe cts the rate of preeclampsia in twin gestations, though the number of subje cts in our study was too small to allow definitive conclusions. Larger stud ies are needed to evaluate this finding.