What to Know About Mercury While Pregnant or Breastfeeding

Medically Reviewed by Dan Brennan, MD on July 28, 2022
4 min read

Mercury is a silvery metal, liquid at room temperature. It exists in three forms — elemental mercury, inorganic mercury compounds, and organic mercury compounds. 

Organic mercury compounds can be dangerous when ingested in food and drink. The association between mercury and pregnancy is particularly worrisome. Unknowingly consuming methylmercury while you are pregnant could harm your baby. 

Mercury occurs in nature. Evaporation from water bodies, degassing from the earth's crust, and emissions from volcanoes release mercury into the environment. Mining, burning fossil fuels, and many industrial processes also release mercury. Mercury exists in the atmosphere chiefly as elemental mercury vapor.

Mercury from industry and other human activities collects in water bodies like the oceans, streams, and lakes. Fish and other animals consume this mercury, which accumulates in their bodies. Eating these fish during pregnancy can cause significant harm to your baby. Mercury passes through the placenta to your baby. It also passes through breastmilk, though in smaller amounts.

Skin-lightening creams are another danger. Some of them contain mercury, which is then absorbed through the skin. Kidney damage can occur after the use of such creams.

Other potential sources of mercury are antique clocks, barometers, and mirrors. Button cell batteries and glass jewelry can also contain mercury.

Methylmercury and other compounds of mercury are hazards. They're absorbed from the intestines and collect in the body. Methylmercury is primarily absorbed from the food you eat. Another compound, dimethylmercury, is absorbed from the skin.

Mercury and pregnancy effects have been known since 1959. Damaged babies were born around Minamata Bay in Kyushu, Japan, and researchers identified methylmercury exposure as the cause. Babies born to women who consumed seafood from the contaminated bay experienced several problems, mainly affecting the nervous system. 

Methylmercury is the form of mercury most often consumed by humans. It is absorbed by the intestines and enters the bloodstream. Methylmercury in the blood during pregnancy travels from placenta to the baby and reaches the brain and other tissues.

Mercury-and-pregnancy is an unfortunate combination. Unborn babies are in a crucial period of development and are highly sensitive to the harms of mercury. Their brain and nervous system are the most affected.

Children born after mercury consumption during pregnancy have a combination of defects known as congenital Minamata disease: 

  • Mental retardation
  • Strabismus (squint)
  • Neck instability
  • Seizures (fits)
  • Poor balance
  • Microcephaly (small head)
  • Lack of eye coordination

The effects of mercury on babies can be subtle, too. Women with higher levels of mercury had children who had lower scores on attention, language, and memory tests, and they displayed reduced coordination, speed, and tactile processing.

You're most likely to consume mercury by eating fish contaminated with mercury. The US Environmental Protection Agency publishes a list of fish that are safe for you to consume while pregnant.

Oily fish (herring, mackerel, salmon, sardines, trout, and others) usually have higher levels of pollutants like mercury. Women who are planning a pregnancy and pregnant/breastfeeding women should not eat more than two portions (140 grams, or 4½ oz. each) of oily fish a week. Young children, pregnant women, and women who are trying to get pregnant should not eat marlin, shark, or swordfish because they contain high levels of mercury. Mercury from these fish stays in your body and may harm a baby in the womb.

Fish collect mercury in their muscles. Trimming the fat or removing the skin will not reduce your mercury exposure if you eat these fish. 

Small fish like sardines and mollusks like scallops contain less mercury. Larger, long-lived fish like shark, marlin, swordfish, tuna, and king mackerel have the highest levels of mercury because they've been collecting it for a long time.

Fish is a valuable part of your diet in pregnancy. It has several nutrients that benefit you and your baby, especially your baby's nervous system and cognitive development. However, you should be careful about choosing fish that are not heavily contaminated by mercury and limit yourself to safe consumption amounts. 

Mercury is also found in fluorescent light bulbs and thermometers. If you accidentally break any of these, that mercury will spill onto nearby surfaces. Using a vacuum cleaner to clean up spilled mercury spreads it into the air. Ask a non-pregnant adult to dispose of spilled mercury by collecting it in a paper sheet.

Dental fillings are sometimes made of mercury mixtures (amalgams). If you need dental treatment during pregnancy, ask your dentist not to use fillings that contain mercury. If you have older fillings with mercury, avoid performing any work on them during pregnancy.

You may be exposed to mercury at your workplace (especially dental offices, mines, electrical or chemical plants, or others). Request work that allows you to avoid mercury exposure for the duration of your pregnancy.

A baby's developing brain and nerves are very susceptible to damage by mercury. Development of the brain continues after birth, and mercury is dangerous at this time. If you are breastfeeding, mercury in your body is transferred into breast milk and consumed by your baby. 

The most common source of mercury in your diet is seafood, so you should be careful about consuming only recommended types and amounts of fish. Fish is good for health, though — don't avoid it altogether. Fish is an important source of protein and provides an alternative to red meat. It also provides several nutrients vital for children's brain development — omega-3 and omega-6 fatty acids, choline, iodine, iron, zinc, and others. 

Mercury is dangerous during pregnancy and breastfeeding. Unfortunately, it is linked to fish and other seafood, which are healthy foods by themselves. Choosing the fish to consume can give you valuable nutrients while keeping your baby safe.