Impact of second trimester iron deficiency on maternal and infant outcomes: A Danish cohort study

Iron is a fundamental component during pregnancy; however, there is a lack of understanding of how iron deficiency (ID) during the second trimester affects maternal and infant outcomes. We aimed to investigate the prevalence of ID among pregnant women during the second trimester of pregnancy and to evaluate the associations with adverse maternal and infant outcomes.

This was an exploratory analysis of data from a longitudinal cohort study including singleton pregnant women at a single center, where P-ferritin was analyzed in blood samples drawn between 24 and 28 weeks gestation. Multivariable regression analyses with Bonferroni corrections were used to evaluate the association between ID (P-ferritin <15 µg/L) in the second trimester and maternal and infant outcomes.

Second trimester ID was found in 182 of the 449 included women (40.5 %), among whom anemia was present in 4.4 %. Women with ID were more often multiparous (73.1 % vs. 52.4 %) and subsequently treated with intravenous iron infusion (5.5 % vs. 1.1 %). Infants born to women with ID had a significantly higher placental weight (700 g vs. 630 g), higher birth weight (3713 g vs. 3522 g), birth weight z-score (0.3 vs. -0.1), and significantly lower prevalence of small for gestational age (2.7 % vs. 9.8 %) compared to women with normal iron levels. ID in the second trimester of pregnancy was not associated with adverse maternal or infant outcomes such as emergency cesarean section, induction of labor, preterm birth, or fetal acidosis.

Despite recommended iron supplements from 10 weeks gestation, ID was frequent among pregnant Danish women in the second trimester and associated with accelerated placental and infant growth, but not adverse pregnancy outcomes. This study indicates that the clinical relevance of the current cut-off level for ID in the second trimester of pregnancy among pregnant Danish women needs further investigation.