Maternal body mass index impacts fetal-placental size at birth and umbilical cord oxygen values with implications for regulatory mechanisms.

BACKGROUND: Maternal under- and over-nutrition are known to effect fetal growth with altered placental development and nutrient transport, but whether fetal oxygenation is also altered remains unknown.

AIMS: To examine linkages between maternal BMI and birth weights, placental weights, and umbilical vein and artery PO2, with implications for signaling mechanisms.

STUDY DESIGN: Population-based cohort study.

SUBJECTS: Analysis of hospital database information on all patients with pre-pregnant BMI values delivering viable, singleton infants between Jan 1, 1999 and Dec 31, 2010 (N=29,212). BMI was categorized into underweight, normal weight, overweight, and obese, with birth weights categorized into small (SGA), appropriate (AGA), and large for gestational age (LGA).

OUTCOME MEASURES: Maternal BMI, birth and placental weights, umbilical vein and artery PO2 .

RESULTS: Underweight mothers with smaller infants and overweight/obese mothers with larger infants had disproportionately large placentas, suggesting compensatory and/or enhanced placental growth in these pregnancies. All SGA infants had lower umbilical vein and artery PO2 , consistent with aberrant placental development leading to diffusional impairment of oxygen. Both maternal overweight/obese BMI and LGA resulted in lower artery PO2 , likely due to increased growth rates with the larger size in these infants.

CONCLUSIONS: These findings support fetal hypoxemia as a common determinant of growth restriction, whether in underweight mothers and due to under-nutrition or in overweight/obese mothers and due to placental insufficiency. However, oxygen is unlikely to be the primary promotor for fetal growth in overweight/obese mothers and LGA infants, with other substrates of more importance as nutritional cues in these pregnancies.