Neonatal Size and Birth Canal Dimensions

Abstract

The limitation of the fetal growth process during pregnancy is supposed to be an adaptative response to a physical or a physiological constraint: the pelvic size or the maternal resources and metabolism. In this study 131 mother-infant dyads were recruited. We investigate correlation between maternal traits (height, BMI) pelvic variables (conjugate diameter, inter-spinous diameter, sub-pubic angle) and neonatal traits (gestational age, birthweight, head, suboccipito-brematic and abdominal girth). We found that the three neonatal variables are significantly inter-correlated. Among maternal traits, height is highly correlated with conjugate and inter-spinous diameters. Subpubic angle is correlated with inter-spinous diameter. Among neonatal and pelvimetry correlations, conjugate diameter is highly correlated with suboccipito-bregmatic girth. The pelvic size seems to be the primary constraint to the fetal growth process. This adjustement of fetus size to the birth canal dimensions limits the risk of dystocia. But the way this adjustement occurs at the end of pregnancy is unclear. We assume that the uterus expansion limitation may be an intermediate mechanism explaining the high correlation between pelvic and neonatal traits.