Placental weight and birthweight: does the association differ between pregnancies with and without preeclampsia?

Placental weight and infant birthweight may be markers of different types of preeclampsia. We studied birthweight within placental weight percentiles in pregnancies with and without preeclampsia.

This was a population study of 317,688 singleton births.

Within the lowest 10% of placental weight, 36% of the offspring were small for gestational age (SGA) in preeclamptic pregnancies and 14% in normotensive pregnancies (relative risk, 2.6; 95% confidence interval, 2.4-2.8). Risk of SGA subsided with increasing placental weight and was negligible at >50th percentile. At low placental weights, large for gestational age (LGA) offspring were nearly nonexistent; however, at >70th percentile, LGA occurred more often in pregnancies with preeclampsia. Within the highest 10% of placental weight, 20.7% of the infants were LGA in the preeclampsia group, and 15.3% of the infants were LGA in pregnancies without preeclampsia (relative risk, 1.4; 95% confidence interval, 1.2-1.5).

In pregnancies with small placentas, the offspring were more often SGA in preeclamptic pregnancies and more often LGA at high placental weights. The results support the hypothesis that preeclampsia may represent different diseases, depending on placental size and infant birthweight.