Fetal dependency on maternal fatty acids: a pilot study in human pregnancies using the natural abundance variation of 13C.

The extent of de-novo biosynthesis of non-essential fatty acids (FA) and the endogenous biosynthesis of long chain PUFA in human fetuses remain largely unknown. We used natural variations in the 13C:12C (δ 13C) of plasma phospholipids of the woman at delivery and of cord blood to infer fetal biosynthesis of FA. We studied thirty-nine mother-fetus pairs with uncomplicated pregnancies and term delivery. Eighteen women were supplemented with DHA, from pregnancy week 20 until delivery, sourced from an algae (n 13) or fish oil (n 5), each with slightly different 13C content. Twenty-one women did not receive DHA supplementation. We measured the δ 13C value of selected phospholipid FA (C16:0, C18:0, C18:1n-9, C18:2n-6, C20:4n-6 and C22:6n-3) in maternal and cord plasma samples at delivery using isotope ratio MS. We found significant linear correlations for δ 13C values of FA between mothers and their fetuses (C16:0, r = 0·8535; C18:0, r = 0·9099; C18:1n-9, r = 0·8079; C18:2n-6, r = 0·9466; C20:4n-6, r = 0·9257 and C22:6n-3, r = 0·9706). Women supplemented with algal DHA had significantly lower DHA δ 13C values in their plasma phospholipids than those supplemented with fish DHA or those who did not receive DHA supplementation (P < 0·001). There was no significant difference in δ 13C values of FA between women at delivery and their fetuses. These findings strongly suggest that the human fetus is highly dependent on the placental transport of maternal plasma FA, particularly DHA. The limited fetal biosynthesis of major FA emphasises the crucial role of maternal nutrition and placental well-being in fetal development.