Fetal sex impacts birth to placental weight ratio and umbilical cord oxygen values with implications for regulatory mechanisms.

Background: We determined the effect of fetal sex on birth/placental weight and umbilical vein and artery oxygen values with implications for placental efficiency and regulatory mechanisms underlying fetal-placental growth differences.

Methods: A hospital database was used to obtain birth/placental weight, cord PO and other information on patients delivering between Jan 1, 1990 and Jun 15, 2011 with GA > 34 weeks (N = 69,836). Oxygen saturation was calculated from the cord PO and pH data, while fractional O extraction was calculated from the oxygen saturation data.