Lamivudine has been evaluated in the Antiretroviral Pregnancy Registry in over 11,000 women during pregnancy and postpartum. Available human data from the Antiretroviral Pregnancy Registry do not show an increased risk of major birth defects for lamivudine compared to the background rate (see Pharmacology: Pharmacodynamics: Clinical Studies under Actions). However, there are no adequate and well-controlled trials in pregnant women and the safe use of lamivudine in human pregnancy has not been established.
There are limited data available on the safety of 3TC in human pregnancy. Studies in humans have confirmed that lamivudine crosses the placenta. Use in pregnancy should be considered only if the benefit outweighs the risk. Although the results of animal studies (see Pharmacology: Toxicology: Pre-clinical Safety Data under Actions) are not always predictive of human response, the findings in the rabbit suggest a potential risk of early embryonic loss.
There have been reports of mild, transient elevations in serum lactate levels, which may be due to mitochondrial dysfunction, in neonates and infants exposed in utero or peri-partum to nucleoside reverse transcriptase inhibitors (NRTIs). The clinical relevance of transient elevations in serum lactate is unknown. There have also been very rare reports of developmental delay, seizures and other neurological disease. However, a causal relationship between these events and NRTI exposure in utero or peri-partum has not been established. These findings do not affect current recommendations to use antiretroviral therapy in pregnant women to prevent vertical transmission of HIV.
Health experts recommend that where possible women infected with HIV do not breast feed their infants in order to avoid the transmission of HIV. Following oral administration lamivudine was excreted in human breast milk at similar concentrations to those found in serum (1 to 8 micrograms/ml). Since lamivudine and the virus pass into breast milk it is recommended that mothers taking 3TC do not breast feed their infants.