How do heavy metals like lead and mercury get from a mother into her baby through the placenta?

What's actually in it

Heavy metals from tap water, food, and household sources circulate in maternal blood during pregnancy. The placenta acts as a partial filter, but it's not effective at blocking heavy metals. Lead crosses most efficiently, followed by mercury and arsenic. Cadmium crosses less readily but still accumulates in the placenta itself, where it causes local damage.

Whatever is in a mother's blood during pregnancy ends up in fetal blood. The fetal brain is forming rapidly and is far more sensitive to these metals than an adult brain.

What the research says

A 2026 study on prenatal maternal-fetal metal levels and placental transfer efficiency characterized how efficiently different metals cross the human placenta. Lead showed the highest maternal-to-cord blood transfer, with fetal levels closely tracking maternal levels. The study found that even mothers with blood lead levels considered low by clinical standards had measurable lead in cord blood.

There's no safe level of lead for fetal brain development. Even very low prenatal exposure is linked to lower IQ, attention problems, and behavioral differences. Mercury affects the fetal nervous system at levels that would be subclinical in adults.

Testing tap water for lead, eating lower-mercury fish, and avoiding high-arsenic foods like rice during pregnancy are the main dietary strategies to reduce metal transfer to the fetus.