05/27/2026
We just don't want it to drop TOO far.
Large cohort and longitudinal studies show ferritin declines from the 1st to the 3rd trimester, even in high‑resource or iron‑supplemented settings.
Studies also find that even as ferritin falls, iron-specific functions often do not (hemoglobin, thyroid hormones, etc.), supporting the idea that some fall in ferritin is adaptive and possibly protective.
The point at which low ferritin becomes a problem depends on the trimester. There is a normal, adaptive 75% drop in ferritin from conception to term, with 50% by GA 28.
So, if a mama is starting with low ferritin early in pregnancy, we can almost predict she will be anemic by the third trimester without supplementation.
However, women with adequate iron stores in the first trimester often do not need iron supplementation and may be harmed by early supplementation.