Background

Pregnancy increases iron needs because of the expansion of maternal blood volume and fetal needs. It is unclear to what extent overweight/obesity (owob) related inflammation during pregnancy influences fractional iron absorption(FIA), iron supply of the fetus and risk of iron deficiency.

Methods

In this multicenter case-control study we included 44 normal weight (nw) and 36 owob women around pregnancy week (PW) 12. We administered 57Fe or 58Fe labeled FeSO4 to women during the 2nd and 3rd trimester of pregnancy. We measured FIA determining erythrocyte incorporation of iron stable isotopes 14 days after administration. From PW 12 until PW 36 iron-, inflammation and hepcidin were monitored. Iron transfer to the fetus was determined as iron stable isotope concentration in cord blood. Sample analysis is currently ongoing, all results will be available in October.

Results

Subject characteristics in PW 12 for the nw (n=26) and owob (n=10) were: mean BMI: 21.4±2.2 and 36.7±6.8 kg/m2, mean hemoglobin: 12.4±1.2 and 12.4±0.9 g/dL and median plasma ferritin: 41.3 (29.6-83.6) and 61.6 (24.3-119.0) µg/L. FIA increase by 2.4 fold in the nw and by 1.3 fold in the owob women between the 2nd and the 3rd trimester of pregnancy. Iron stores decreased in both groups over the course of pregnancy. Hepcidin was still significantly higher in the owob women in the 3rd trimester. Inflammation tended to be higher in ow/ob women throughout pregnancy. Iron isotopes were highly detectable in cord blood. The 58Fe:57Fe-ratio determined in cord blood corresponded to the 58Fe:57Fe-ratio determined in the mother in the 3rd trimester.

Conclusions

ow/ob women, the increase in FIA throughout pregnancy to support iron needs of mother and fetus is blunted compared to nw women. This is consistent with elevated hepcidin in the 3rd trimester and higher inflammation throughout pregnancy. Thus, even though iron demands are strongly increased, owob may prohibit an adequate iron supply to the expecting mother and the fetus due to