AbstractsSome investigators think that placental size is just a manifestation of fetal growth and has no independent clinical significance. There are, however, cases in which abnormal-sized placentas are the result of clinically important disorders. The present study attempted to identify the factors that affect placental growth. The information thus obtained was used to determine if relative placental underweight and overweight have independent correlations with perinatal health and childhood growth and development.The data for the study came from the Collaborative Perinatal Study (CPS) of the National Institute of Neurological and Communicative Disorders and Stroke. The CPS followed the course of more than 55,000 pregnancies in 12 medical school-affiliated hospitals in different regions of the United States between 1959 and 1966 by recording (prospectively) events of gestation, labor, and the neonatal period. Placental weight and other data were available from 38,351 single-born children (20,724 white and 17,627 black), 65 per cent of whom were available for follow-up at 7 years of age. This made it possible to determine if abnormal placental size has any long-term correlation with the growth and development of children.All but two of the 10 factors that had significant positive or negative correlations with birth weights had similar correlations with placental weights (Table 1). The two exceptions were cigarette smoking and short maternal stature, neither of which affected placental weight significantly.A placental growth table and percentile growth charts were constructed, taking into consideration the factors that had the greatest influence on placental weights, i.e., maternal pregravid body weight, race, pregnancy weight gain, and gestational blood pressure (Table 2, Figs. 1 and 2). Baseline placental weights in Table 2 are for normotensive women who weighed 48 to 66 kg before pregnancy and gained 6 to 14 kg during pregnancy. Adjustments in placental weights for gravidas in different body-weight and weight-gain categories are found in Table 2. After these adjustments are made, the weight percentile for any placenta can be determined from the curves in Figures 1 or 2.Relatively low placental weight was associated with higher-than-expected hemoglobin values in newborns. Relative placental underweight was associated also with small body size at 7 years of age, independent of the factors that have the greatest effect on placental growth. The latter correlation was present in blacks but not in whites.Neonatal manifestations of acute or subacute antenatal hypoxia, including death and neurological abnormalities, were most frequent when placentas were relatively overweight. These effects were greatest before 35 weeks of gestation and decreased progressively toward term. Some of the neurological abnormalities present in newborns with overweight placentas persisted into later childhood. At 7 years of age, 5.6 per cent of the children whose placentas had been overweight demonstrated neurological abnormalities, compared with 4.2 per cent of the children whose placentas had been of normal weight (P <0.001). Relative placental underweight was not followed by long-term neurological abnormalities.