Maternal BMI, Mid-Pregnancy Fatty Acid Concentrations,and Perinatal Outcomes.

PURPOSE: Maternal body mass index (BMI) and systemic fatty acid (FA) concentrations affect inflammatory balance in pregnancy and play a key role in fetal growth and well-being. Little is known about how maternal BMI may affect the association between key FA concentrations and neonatal outcomes. The objective of this study was to examine the associations between the maternal omega (n)6:n3 FA ratio and neonatal outcomes according to maternal pre-pregnancy BMI category.

METHODS: This study is a secondary analysis of the Maternal-Fetal Medicine Units Network randomized controlled trial of omega-3 FA supplementation to prevent recurrent preterm birth. At consent (16-22 weeks of pregnancy), women were randomized to either the intervention arm (2g of n3 FAs) or the control arm (placebo). For the present analysis, the primary exposure was the ratio of proinflammatory to anti-inflammatory (n6:n3) FAs at 25 to 28 weeks of pregnancy. The primary outcome was fetal growth as measured by using birth-weight-for-gestational-age z score, birth-length-for-gestational-age z score, and head-circumference-for-gestational-age z score. BMI categories were defined as lean (18.5-24.9 kg/m²) and overweight/obese (OWOB) (≥25.0 kg/m²). Final analysis was stratified according to BMI and adjusted for education, race, parity, smoking status, total fish intake at the time of the blood draw, and number of days in the study at the time of delivery.

FINDINGS: A total of 440 participants were included in this analysis; 49% were lean, and 51% were OWOB. After adjustment for covariates, a higher maternal n6:n3 FA ratio was associated with impaired fetal growth (birth-weight-for-gestational-age z score, β = -0.04 per unit increase in n6:n3; 95% CI, -0.07 to -0.01), 1day shorter length of gestation (β = -0.14 week; 95% CI, -0.27 to -0.01), higher incidence of neonatal respiratory distress syndrome (odds ratio, 1.37; 95% CI, 1.04 to 1.80), and increased length of neonatal hospital stay (β = 0.29 day; 95% CI, 0.003 to 0.58) in OWOB, but not lean, participants.

IMPLICATIONS: Higher maternal inflammation during pregnancy, as measured by using the n6:n3 FA ratio, may be a marker of adverse perinatal and neonatal outcomes, particularly among OWOB women.