Reference weights for placentas delivered before the 28th week of gestation.

CONTEXT Very few studies have measured the weight of large numbers of placentas delivered before the 28th post-menstrual week. METHODS We measured the weight of 930 singleton placentas delivered before the 28th post-menstrual week, and examined the distributions of weights in selected groups (week of gestation, reason for preterm birth, birth weight Z-score categories, placenta histology). We excluded 90 singleton placentas based on growth restriction as indicated by birth weight Z-score, resulting in a normative sample of 840 placentas. Weights for unfused twin placentas are also presented. RESULTS Standard weights derived from our data set differ from those previously published, partly due to a larger sample size. Placenta weight varied with birth weight. Placentas from pregnancies ending due to preeclampsia, fetal indications or those showing evidence of poor perfusion on histology were among the smallest and their weights correlated with the smallest birth weights for gestational age. CONCLUSIONS Placenta weights appear to be influenced by multiple maternal and fetal processes. We present a standard weight table for singleton placentas among live infants born between 23 and 27 completed weeks.