Is iron before pregnancy safe during pregnancy?

What does the evidence say about iron before pregnancy during pregnancy?

1. Iron needs are 18 milligrams a day for women aged 19 to 50 and 27 milligrams a day in pregnancy, with a tolerable upper intake level of 45 milligrams a day from all sources. 1
2. About 18 percent of pregnant people in the United States have iron deficiency, and the rate climbs from 6.9 percent in the first trimester to 29.7 percent in the third. 1
3. Insufficient iron in pregnancy raises the risk of low birthweight, premature birth, low infant iron stores, and impaired cognitive and behavioral development. 1
4. In a prospective cohort of 18,555 women followed for eight years, those who used iron supplements had a significantly lower risk of infertility from an ovulatory disorder than non-users, with a relative risk of 0.60, while heme iron intake showed no relationship. 2
5. Prenatal vitamins are designed to carry the recommended daily vitamins and minerals for before and during pregnancy, including folic acid and iron, and most contain the 27 milligrams a day pregnancy requires. 3

Is iron before pregnancy safe in each trimester?

• First trimester. Preconception is the easiest time to correct low iron, because you have months rather than weeks and no pregnancy nausea competing with the tablet. In the Nurses' Health Study II, people who used iron supplements had a lower risk of ovulatory infertility than non-users. That is an observational finding, not a fertility claim, but it makes the preconception check worth doing.
• Second trimester. Requirements are already at their pregnancy level of 27 milligrams a day, and most prenatal vitamins include that amount. Iron deficiency rises steadily through pregnancy in United States data, from 6.9 percent in the first trimester to 29.7 percent in the third, so this is the point to act on any bloodwork rather than wait.
• Third trimester. This is where deficiency peaks. Insufficient iron in pregnancy is linked to low birthweight, premature birth, low infant iron stores, and impaired cognitive and behavioral development. Constipation from iron is common now; ask your provider about form and timing rather than quietly skipping doses.