Are Iron Supplements Taken in Pregnancy Related to a Baby’s Growth?

Recently researchers at the University of Cambridge engaged in a research project to determine the if taking iron supplements during pregnancy is connected with the speed at which an infant grows and other biological factors associated with the growth and nutritional status of a child. The general idea behind the study is to understand whether the typical iron supplements recommended to women as part of prenatal care are having unintended effects. Based on prior research, the researchers at Cambridge knew that iron supplements seemed to increase the size of an infant and the percentage of body fat that an infant has at birth. The prior thinking was that this could be caused by a risk of diabetes that the baby has in the womb (gestational diabetes). The researchers set out in this study to see if iron supplements affected the growth, glucose tolerance (ability to use sugar in the body), and blood pressure of children. These potential changes are labeled as nutritional programming – when exposure to a certain nutritional environment in the womb affects the baby’s health after birth.

Method for Answering the Question

The research study was conducted from 2001 to 2009. 2,229 pregnant women were recruited to the study (Cambridge Baby Growth Study) from ultrasound clinics in a hospital in Cambridge, UK. The research participants were asked to complete a pregnancy questionnaire as their pregnancy moved forward. The questionnaires were then collected after the birth. During the study, 571 women dropped out leaving 1,658 for the first part of the study. For the babies that were enrolled in the study through the mothers, the racial/ethnic characteristics were: 95% White, 1.3% Black (African or Caribbean), 1.7% Asian, and 1.7% mixed race. Women in the study were divided into those taking iron supplement during their pregnancy and those were not taking iron supplements. Information was collected on any diseases that the women had during the study. During the study some additional women were removed if their questionnaires were not complete or they met some other criteria for removal.

Different indicators of growth were used for babies at different time periods: 3, 12, and 24 months. The weight of infants was determined from hospital records. Some of the other factors measured included length or height, head circumference (distance around the head), length of waistline, and skinfold thickness (a way to estimate body fat). This was done for 341 infants who had mothers taking supplemental iron and 222 infants whose mothers did not. A smaller group of children had measurements of growth and whether they were likely to have diabetes or high blood pressure at 9 years of age.


The results of the study are quite interesting for the mothers who used iron supplements during pregnancy. At 3 months, their infants had more body fat as measured by skinfold thickness and waistlines. However, there were no differences in other factors including weight, head circumference and height. Between 3 and 12 months, there was a significant drop in the skinfold thickness measurement for infants whose mothers used iron supplementation compared to those who did not. At 12 months old, the only difference was a larger waist circumference. At 24 months of age, there were no differences. Overall, the larger size of the child seemed to occur early in life.

What does this mean for the future?

These results help answer the question of whether iron supplementation by a pregnant woman can increase the size of children. At 3 months, children are larger, but they become more similar as they age. Parents worried about iron setting their child up for having diabetes or some other disease can benefit from this info. The study also found that older children (mid-childhood) had one difference – blood pressure in arteries. Other indicators remained similar for the groups. The researchers indicate that iron supplementation seems to offer benefits to children early on but that decreases over time. During that period, children can be given supplements or a multivitamin, as appropriate. Working closely with clinicians, parents can figure out the best plan for their baby before and after birth. The results of the study show that it is great news for mothers who used iron supplementation in the past and also currently pregnant women. Anemia is a common challenge for some pregnant women, and iron is often one key way to combat this.

Perry Payne
Dr. Perry Payne is a public health practitioner and scholar with expertise in quality of care, health equity, prescription drug policy, and health care ethics. He has over ten years of experience as a freelance health care/medical writer and editor. His full-time work experience includes working as a professor and researcher in universities, serving as a federal government official, and a brief stint working for healthcare technology companies.

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