EXPOSURE TO INORGANIC AND ELEMENTAL MERCURY IN PREGNANCY

There are three forms of mercury: elemental (metallic) mercury (a heavy silver-white metallic element), inorganic mercury, and organic mercury. It is important to distinguish between these forms as risk of toxicity is dependent on the chemical form of the metal as well as the route of exposure. Inorganic mercury is primarily found in batteries, disinfectants, art pigments, and in some traditional remedies and cosmetics. Poisoning may occur following ingestion, injection, inhalation or dermal absorption. Elemental mercury occurs naturally in the environment and is used in the production of dental amalgam, thermometers and electric light bulbs. Elemental mercury is poorly absorbed by the skin and GI tract but readily absorbed if inhaled as mercury vapour, potentially resulting in toxic effects. 

There are few published reports that focus specifically on the possible adverse reproductive or fetal effects following acute exposure to inorganic or elemental mercury compounds in human pregnancy. The small number of available studies on exposure to dental amalgam fillings provide no evidence of an association with effects on birth weight, gestational age at delivery, or stillbirth. Published data on chronic occupational exposure also provide no evidence of an association between in utero exposure to inorganic or elemental mercury and the occurrence of congenital malformation, miscarriage, stillbirth or low birth weight in the offspring. However, the limited and retrospective nature of these studies renders them unsuitable for use in a formal risk assessment and therefore an increase in risk cannot be ruled out, and not all pregnancy outcomes have been adequately studied to inform a risk assessment. Where exposure to inorganic or elemental mercury occurs, associated maternal toxicity is likely to be a major determinant of risk to the fetus. Treatment of the mother should not be delayed or withheld on account of pregnancy and should be as for the non-pregnant patient. 

As with all chemicals, unnecessary exposure to inorganic or elemental mercury should be avoided during pregnancy. However, where occupational exposure is unavoidable, adequate health and safety precautions should be taken to ensure that exposure is well within recommended limits to reduce the risk of maternal toxicity.

Inadvertent exposure to inorganic or elemental mercury at any stage in pregnancy would not usually be regarded as medical grounds for termination of pregnancy. However, other risk factors may be present in individual cases which may independently increase the risk of adverse pregnancy outcome. Clinicians are reminded of the importance of consideration of such factors when performing case-specific risk assessments. Where exposure to inorganic or elemental mercury has occurred, even in the absence of maternal toxicity, enhanced fetal monitoring may be warranted. Once the mother has been assessed and treated, discussion with UKTIS regarding fetal risk is recommended.