Maternal but not fetal <em>FADS</em> gene variants modify the association between maternal long-chain PUFA intake in pregnancy and birth weight.

Several studies have shown a positive association between maternal fish intake in pregnancy and pregnancy duration and child birth weight (BW), probably due to fish n-3 (&omega;-3) long-chain polyunsaturated fatty acids (LC-PUFAs). n-3 LC-PUFAs can also be synthesized endogenously, and their synthesis depends on single nucleotide polymorphisms (SNPs) in the fatty acid desaturase (FADS) gene encoding for FADS. We assessed the associations of maternal docosahexaenoic acid (DHA) intake in pregnancy with pregnancy duration and BW and investigated whether these associations are modified by maternal or fetal FADS SNP genotypes. We hypothesized that we would find stronger associations in minor allele homozygous mothers or fetuses due to their lower n-3 LC-PUFA endogenous synthesis and hence higher dependence on dietary supply. Data on maternal diet, pregnancy duration, and BW were available for 2622 mother-child pairs from the KOALA (Kind, Ouders en gezondheid: Aandacht voor Leefstijl en Aanleg) Birth Cohort Study. The rs174556 FADS SNP was genotyped in 1516 mothers and 1515 children. Associations and gene-diet interactions were tested with linear regression adjusting for potential confounders, including intake of other PUFAs. Women at the 75th percentile of DHA intake had 0.7-d longer pregnancies (P = 0.016) and 28-g heavier infants (P = 0.039) than did women at the 25th percentile of intake. Associations with arachidonic acid intake were of the same order but in the opposite direction. Mothers who were homozygous for the minor allele had 2-d shorter pregnancies (P = 0.035) and infants who were nearly 140 g lighter (P = 0.006) than did mothers who were major allele homozygotes. Post hoc analyses revealed that they had higher prepregnancy BMI (P = 0.020). Among the women homozygous for the minor allele, those at the 75th percentile of DHA intake had 226-g heavier infants than those at the 25th percentile of intake (P = 0.030), whereas DHA intake was not significantly associated with BW in major allele carriers. These findings suggest that maternal and fetal fatty acid requirements during pregnancy depend on maternal genetic variation in LC-PUFA synthesis