Maternal long-chain polyunsaturated fatty acid status, methyl mercury exposure and birth outcomes in a high fish-eating mother-child cohort

Background: Maternal status of long-chain polyunsaturated fatty acids (LCPUFAs) may be related to fetal growth. Maternal fish consumption exposes the mother to the neurotoxicant methylmercury (MeHg), which in contrast may restrict fetal growth. Objective: Our aim was to examine relationships between maternal LCPUFA status at 28 weeks and birth outcomes (birth weight, length and head circumference), controlling for MeHg exposure throughout pregnancy, in the Seychelles Child Development Study Nutrition Cohort 2. Our secondary aim was to examine the influence of maternal variation in genes regulating the desaturation of LCPUFAs (fatty acid desaturase (FADS)) on birth outcomes. Methods: From non-fasting blood samples collected at 28 weeks gestation, we measured serum total LCPUFA concentrations and FADS1 (rs174537, rs174561), FADS1-FADS2 rs3834458 and FADS2 rs174575 genotypes, with hair total mercury (Hg) concentrations assessed at delivery. Data were available for n=1236 mother-child pairs. Associations of maternal LCPUFAs, MeHg and FADS genotype with birth outcomes were assessed by multiple linear regression models, adjusting for child sex, gestational age, maternal age, BMI, alcohol use, socioeconomic status and parity. Results: In our cohort of healthy mothers, neither maternal LCPUFA status nor MeHg exposure were significant determinants of birth outcomes. However, when compared to major allele homozygotes, mothers who were heterozygous for the minor allele of FADS1 (rs174537 and rs174561, GT vs TT, β=0.205, P=0.03; TC vs CC, β=0.203, P=0.04) and FADS1-FADS2 (rs3834458, Tdel vs DelDel, β=0.197, P=0.04) had infants with a greater head circumference (all P<0.05). Homozygosity for the minor allele of FADS2 (rs174575) was associated with a greater birth weight (GG vs CC, β= 0.109, P=0.04). Conclusions: In our mother-child cohort, neither maternal LCPUFA status, nor MeHg exposure were associated with birth outcomes. The observed associations of variation in maternal FADS genotype with birth outcomes should be confirmed in other populations.