Many women take prenatal vitamins before, during and after a pregnancy, often on the advice of their OB-GYN. Some doctors will write a prescription for one, others suggest over-the-counter brands. Both of these types will contain iron, some as much as 45 mg in a single tablet or capsule. Not surprising since the CDC and the American College of Obstetricians and Gynecologists recommend universal consumption of prenatal supplements containing iron to meet pregnancy needs and to prevent anemia.
A woman has an increased need for iron during pregnancy as her blood volume expands and the demands of her growing baby and placenta increase. According to WEBMD.com, she needs 27 mg per day during pregnancy, and 9 during lactation; this mirrors the Institute of Medicine recommendations.
A large percentage of women have iron deficiency during their reproductive years. What about during pregnancy? Iron deficiency prevalence during pregnancy increases with each trimester, 7% of women in the first, 14% in the second, and 30% in the third trimester test positive for it (1). So it would seem to make good sense to take a vitamin supplement with iron during pregnancy. But let's take a closer look.
What are the risks of iron deficiency during pregnancy? According to the National Library of Medicine at NIH:
"There are more than 60 studies on the use of iron supplements in pregnancy. A total of more than 30,000 women took part in the studies. The results show that, if women have normal blood values, taking 30 mg of iron per day as a precautionary measure does not have any noticeable health benefits for them or for their children. Although iron supplements were found to lower the risk of anemia, they did not influence the number of preterm births or infections in pregnant women." (2)
For some women, however, iron supplementation for all three trimesters may not always be the best course of action. Iron seems to be one of those "Goldilocks" nutrients - you don't want too much, or too little, just about right is ideal.
Beyond the more immediate side effects of higher doses of supplemental iron to a woman: constipation, nausea, and even vomiting in excess of what is normal during pregnancy, high body stores of iron (as measured by higher serum ferritin levels) appear to be linked to an increase in the risk for gestational diabetes. A blood test for ferritin can be good indicator of body stores of iron, but the test is affected by the body's level of inflammation. Pregnancy is considered an "inflammatory state", so measuring serum ferritin during pregnancy may or may not reflect the actual body stores of iron for a given woman (3).
My recommendation would be to get your serum ferritin checked prior to conception, along with a marker of inflammation such as hsCRP. Your doctor can then evaluate your need for iron supplementation well before or at the onset of your pregnancy, and monitor you throughout your gestation to see if and how your status changes.
You might want to consider those two tests (serum ferritin and hsCRP) at least 6 months prior to an anticipated pregnancy, so you can increase your dietary intake of iron-rich foods such as red meat, dark chicken, liver, and/or supplement with a high quality, easy-on-the stomach formula such as Feosol, as needed. Follow this with another check just before you "start trying" to conceive.
It is possible that the same metabolic problems that lead to gestational diabetes are contributing to a rise in ferritin in some women. If your ferritin is elevated as evaluated by your doctor (or for example above 150-200 ng/mL and no substantial elevation in hsCRP) you may want to consider monitoring your own blood glucose (see a previous post here on "Gestational Pre-diabetes" http://www.womenandfamilynutrition.com/blog/2016/2/27/second-post), especially if you or anyone in your family has a history of GDM.
Finally, please be aware that what may look like iron deficiency anemia could have other contributing factors, nutritionally speaking: vitamins A, B6, folate, B12, and the minerals zinc and copper play roles in the formation of red blood cells. Vitamin A and B6 are particularly difficult for many women to obtain from their diet - see my articles published in the Wise Traditions Journal for reasons behind that and what to do diet-wise (4,5). Zinc can also be problematic especially if a women has been on oral contraceptives for a number of years.