Should I check my iron levels before getting pregnant?

Why iron, and why before pregnancy

Iron carries oxygen and helps build the brain's wiring. Women aged 19 to 50 need 18 mg a day. In pregnancy that rises to 27 mg, because your blood volume grows and you need extra iron for all those new red blood cells.

Your baby is also saving iron. A baby born at full term usually has enough stored to last about the first 4 to 6 months, and those stores are built in the womb, from you.

The problem is timing. In US national data, 18% of pregnant women were iron deficient. That figure rose from 6.9% in the first trimester to 14.3% in the second and 29.7% in the third. It more than quadruples. Coming in with full stores, and keeping them topped up, is much easier than catching up late.

Ask for ferritin by name

Here's the detail that trips people up. A standard blood count looks at hemoglobin, which only falls after your iron stores are used up. Ferritin measures the stores themselves. The NIH says ferritin can show iron running low at an early stage, before anemia appears.

“Not anemic” and “plenty of iron” aren't the same thing. A study in Ireland followed 189 healthy first-time mothers who were not anemic. Those with low iron stores (ferritin under 30 µg/L) at 15 weeks had babies with lower iron in their cord blood, and at age 2 their children scored a little lower on language and movement tests. It was small and observational, so it shows a link, not proof.

So at your preconception visit, say: “Can you include ferritin, not just hemoglobin?” It belongs on the list with your thyroid and blood sugar tests (see preconception blood tests).

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Who is more likely to start low

• Heavy or long periods. Monthly blood loss makes a low starting point more likely.
• Vegetarians and vegans. Plant iron is absorbed less well, so vegetarians need about 1.8 times as much iron.
• A recent pregnancy or breastfeeding. If you've had a baby in the last year or two, your stores may not have refilled. See how long to wait between pregnancies.

None of these mean you're low. They mean it's worth knowing your number.

What the research links to early anemia

In a Swedish registry study of 532,232 children, a mother's anemia diagnosed in the first 30 weeks of pregnancy was linked with higher rates of autism (4.9% vs 3.5%), ADHD (9.3% vs 7.1%) and intellectual disability (3.1% vs 1.3%), while anemia diagnosed later in pregnancy showed no such link.

It's a registry study, so it can't prove cause, and the researchers didn't measure iron itself. The absolute risks stayed low. But it points at the early months, and the early months start with the iron you bring in.

The NIH adds that low iron in pregnancy raises the baby's risk of low birthweight, preterm birth, low iron stores and slower thinking and behavior development.

The iron story keeps going after birth

The iron you bring into pregnancy becomes your baby's starting supply, and there are two more chances to add to it.

At birth. In a Cochrane review of 15 trials, babies whose cords were clamped early were more than twice as likely to be iron deficient at 3 to 6 months. For a healthy baby, waiting until the cord stops pulsing, as your birth team advises, lets more blood and iron reach your baby. It's worth adding to your birth plan and discussing with your birth team.

At first foods. The iron banked at birth needs topping up from food around 6 months, and the CDC advises starting with solids that contain iron. Long-term studies found that young adults who had chronic, severe iron deficiency as babies did worse at 19 on tests of planning, memory and self-control. Those studies were observational, but the message is simple: iron is a thread that runs from before conception to the high chair, and checking it early is the easiest place to start.

Test, don't guess: building iron safely

More iron isn't automatically better. A Chilean trial found that extra iron didn't help babies who already had plenty and may have done slight harm. The same “test, don't guess” rule makes sense for adults. The safe upper limit is 45 mg a day. If your doctor says you need a supplement, take what they recommend. Don't add extra “just in case.”

Food comes first. Iron from meat, poultry and seafood (heme iron) is absorbed best. Plant iron absorbs better with vitamin C on the same plate.

Figures from the NIH Office of Dietary Supplements.

Easy pairings: lentil soup with lemon, fortified cereal with strawberries, bean tacos with salsa. Calcium may reduce iron absorption, so if you take an iron pill, ask whether to take it apart from milk or a calcium supplement. Beef liver is iron-rich but very high in vitamin A, so skip liver and liver products like pâté in pregnancy, as the NHS advises. Once you're pregnant, ACOG recommends anemia screening for everyone; ask whether your iron will be rechecked in the third trimester, when it runs lowest. More in low iron in pregnancy.

Go deeper

Grow a Genius

In the book: Chapter 6: The Preconception Check-Up

Grow a Genius follows iron from the preconception check-up through the third trimester and first foods, with the tests to ask for at each stage and iron-rich recipes in The Genius Kitchen.

• The 7 Genius Builders, stage by stage
• 16 printable guides, including the Prenatal Label Decoder
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