Maternal iron status in early pregnancy and birth outcomes: insights from the Baby’s Vascular health and Iron in Pregnancy study

Iron deficiency anaemia during early pregnancy has been linked with low birth weight and preterm birth. However, this evidence comes mostly from studies measuring haemoglobin levels rather than specific measures of iron deficiency. This study aimed to examine the association between maternal iron status during the first trimester of pregnancy, as assessed by serum ferritin, transferrin receptor and their ratio, with size at birth and preterm birth. In the Baby VIP (Baby’s Vascular health and Iron in Pregnancy) study we recruited 362 infants and their mothers after delivery in Leeds, UK. Biomarkers were measured in maternal serum samples previously obtained in the first trimester of pregnancy. The cohort included 64 (18%) small for gestational age (SGA) babies. 33 babies were born preterm (9%; between 34-37 weeks). First trimester maternal iron depletion was associated with a higher risk of SGA (adjusted OR 2.2, 95% CI 1.1, 4.1). This relationship was attenuated when including early pregnancy haemoglobin in the model, suggesting it as a mediator (adjusted OR 1.6, 95% CI 0.8, 3.2). For every 1g/dl increase in maternal haemoglobin level in the first half of pregnancy the risk of SGA was reduced by 30% (adjusted 95% CI 0-40%); levels below 11 g/dl were associated with 3 fold increase in the risk of SGA (95% 1.0, 9.0). There was no evidence of association between maternal iron depletion and preterm birth (adjusted OR 1.5, 95% 0.6, 3.8). This study shows that depleted iron stores in early pregnancy are associated with higher risk of SGA.