Atenolol crosses the placenta and is excreted in breast milk where concentrations higher than those in maternal plasma have been achieved.
Pregnancy and the Neonate: In 6 women who had taken atenolol for at least 6 days up to the time of delivery, concentrations of atenolol in maternal and umbilical serum were approximately equal. Furthermore, in a woman who had discontinued treatment 1 day before delivery, atenolol was not found in maternal or umbilical serum. The half-life of atenolol in neonates born to mothers who had been receiving atenolol ranged from 10.5-34.6 hrs (mean 16.1 hrs) in a study of 35 term infants. Atenolol concentrations were determined in cord blood and in neonatal blood 24 hrs after delivery. The range of elimination rate was 4 times slower than in adults, a difference expected based on renal excretion of atenolol.
Atenolol diffuses into breast milk and is present in milk in concentrations similar to or higher than those in maternal blood. Bradycardia associated with ingestion of atenolol in breast milk has been reported in a 5-day old term infant. The baby improved when breastfeeding was discontinued.
Use in pregnancy: Safety in pregnancy has not been established, therefore, atenolol is not recommended for use in pregnant women or those likely to become pregnant, unless the expected benefit outweighs the potential risk. Atenolol has been used effectively under close supervision for the treatment of pregnancy-associated hypertension. There was no evidence of any fetal abnormalities, although atenolol was generally given after 20 weeks of gestation.