Gross placental structure in a low-risk population of singleton, term, first-born infants.

Suboptimal fetal growth has been associated with an increased risk of adult disease, which may be exacerbated by an increased placental weight-to-fetal weight ratio. Placental weight is a summary measure of placental growth and development throughout pregnancy. However, measures of placental structure, including the chorionic disk surface area and thickness and eccentricity of the umbilical cord insertion, have been shown to account for additional variance in birth weight beyond that explained by placental weight. Little is known of the variability of these placental parameters in low-risk populations; their association with maternal, pregnancy, and neonatal characteristics; and the agreement between manual and digital measures. This study used manual and digital image analysis techniques to examine gross placental anatomy in 513 low-risk, singleton, term, first-born infants. Parametric methods compared groups and examined relationships among variables. Maternal birth weight, prepregnancy weight, and body mass index were associated with increased placental and birth weight (all P < 0.005), but only maternal birth weight was associated with increased placental surface area (P < 0.0005) and thickness (P = 0.005). Smoking during pregnancy reduced birth weight and increased the eccentricity of umbilical cord insertion (P = 0.012 and 0.034, respectively). The variability in these placental parameters was consistently lower than that reported in the literature, and correlations between digital and manual measurements were reasonable (r = .87-.71). Detailed analyses of gross placental structure can provide biologically relevant information regarding placental growth and development and, potentially, their consequences.