To date the beta-adrenoceptor blocking drugs have not been associated with an increased risk of structural malformations. Some recent studies have suggested a possible increased risk of congenital heart defects associated with antihypertensive therapy including beta-adrenoceptor blocking drugs, however it is unclear whether any risk is due to the underlying maternal condition or the medications. The use of beta-adrenoceptor blocking drugs in the first and second trimesters of pregnancy has been associated with intrauterine growth retardation (IUGR) and low birth weight.