Increase in normal placental weights related to increase in maternal body mass index

Reference values of normal placental weights are many decades old. Recently, a trend of increasing weights of normal placentas has been noted. We aimed to confirm this observation and to find any associated fetal and maternal factors.

Information on all live singleton deliveries that met our inclusion criteria was collected for the years 1995 and 2004 at Creighton University Medical Center in Omaha, Nebraska. This information was compared to the standards set forth in the older references. The Student's t-test and correlation-regression statistics were applied.

The mean weight of the mature, term (37-42 weeks of gestation) placenta has increased significantly from 1995 to 2004 (499 g to 537 g, p = 0.02), as well as from the older standards (27% increase at 40 weeks of gestation). There has also been a significant increase in the maternal body mass index (BMI) from 1995 to 2004 (25.2 to 26.5, p = 0.02), which correlates with maternal weight gain during pregnancy, and fetal and placental weights.

Normal placental weights have increased over the last decades and this may correlate with increasing maternal obesity. Further studies with larger populations are needed to confirm these findings.