Trace Metals in Early Pregnancy Alter Thyroid and Baby Size

Trace metals in a pregnant woman's body during the first trimester change her thyroid hormones later in pregnancy and affect how big her baby is at birth.

What the Study Found

A 2026 study in Biol Trace Elem Res tracked 1,351 pregnant women in Shanghai. They measured seven trace elements in the first trimester: vanadium, chromium, manganese, cobalt, nickel, arsenic, and selenium. Then they checked thyroid hormones in the third trimester and measured the babies at birth.

Chromium was the primary driver. Higher chromium exposure was linked to increased TT3 (a thyroid hormone), longer birth length, and larger head circumference. Higher selenium also increased head circumference. Arsenic raised TSH levels.

Too Little or Too Much Is Bad

The relationship wasn't straightforward. Arsenic, chromium, and vanadium all showed U-shaped curves with thyroid hormones. That means both very low and very high levels disrupted thyroid function. There's a narrow healthy range, and many women fall outside it.

Where These Metals Come From

Chromium is in stainless steel cookware, leather products, and some supplements. Arsenic is in rice, drinking water, and some fruit juices. Vanadium comes from fossil fuel burning and some foods. These aren't exotic exposures. They're everyday ones.

How to Protect Yourself During Pregnancy

Vary your grain sources to reduce arsenic from rice. Filter drinking water. Be cautious with chromium supplements. Check out non-toxic baby products for a safer start.

Also see glass food storage for safer alternatives.

Source: Wu T, et al. (2026). Biol Trace Elem Res.