Lead, cadmium and mercury levels in pregnancy: the need for international consensus on levels of concern

For heavy metals that have any degree of transfer though the placenta to the fetus, it is unlikely that there are safe limits for maternal blood levels.
The only means of reducing fetal exposure is to minimise maternal exposure. There are few recommendations for levels of concern. With the
exception of US recommendations for maternal Pb levels, but there are no international levels of concern or cut-off levels specifically for pregnancy
for heavy metals, so that comparisons can generally only be made with national reference values relating to similar physiological statuses or age
groups. These include recommendations for Cd levels by Germany (reference value for non-smoking adults aged 18–69 years, 1 µg/l) and for Hg
by Germany (reference value for adults age 18–60 years with fish intake ⩽3 times per month, 2.0 µg/l) and the USA (cut-off level for women,
5.8 µg/dl). To illustrate the lack of cohesion, we present data on blood Pb, Cd and Hg levels from pregnant women enroled in the UK Avon
Longitudinal Study of Parents and Children study and compare the values with present levels of concern and recommended cut-off values. We also
compare the levels with those found in other groups of pregnant women worldwide to strengthen the database for the development of levels of
concern in pregnancy. The need for clarity of terminology in describing levels of concern is discussed. There is a pressing need for international
consensus on levels of concern for all age groups and physiological statuses, particularly for pregnancy.