A large epidemiological study from the United States on statin use in the first trimester of pregnancy has found no evidence of a teratogenic effect. However, the study authors concluded that further research is needed before statins can be considered safe in pregnancy.

A cohort of 886,996 pregnancies was collected over an eight-year period from 2000 to 2007. All the women received care exclusively on the Medicaid programme with data collection starting at least three months prior to the index pregnancy and running continuously through to at least one month following it.

A total of 1,152 (0.13%) women filled a prescription for statins during the first trimester. Data on the use of the seven statins available during the study period were collected and combined.

Data on maternal comorbidity for example hypertension, renal disease, obesity, hyperlipidaemia, and pre-existing diabetes, and tobacco, alcohol and illicit drug use were recorded.

The primary outcome was the occurrence of a congenital abnormality in the infant.

Women who used statins tended to be older and less likely to be of African-American origin. They were more likely to have comorbidities, especially diabetes and to have been exposed to oral hypoglycaemic agents.

Congenital malformations were present in 6.34% (n = 73) of the statin exposed pregnancies and 3.55% (n = 31,416) in unexposed pregnancies; unadjusted relative risk (RR) for malformations in statin-exposed pregnancies 1.79 (95% CI: 1.43-2.23). Central nervous system and cardiac abnormalities were significantly more common in the statin-exposed pregnancies. However, after controlling for pre-existing diabetes and other confounders the RR of any congenital abnormality dropped to a statistically insignificant value, RR 1.07 (95% CI: 0.85-1.37).

Although this study provides reassurance about the use of statins in pregnancy, as with any observational study, it was open to bias and its findings offer guidance rather than proof. It seems reasonable to continue advising women not to conceive while taking statins especially as more subtle neurodevelopmental and infant behaviour effects were not addressed.

The study authors caution:

‘Our analysis did not find a significant teratogenic effect from use of statins in the first trimester. However, more information about the long-term effects of in utero exposure to statins and about the effect on other neonatal outcomes, as well as replication of our findings in other large datasets with well measured information on statin use, confounders, and outcomes, are needed before statin use during pregnancy can be considered safe.’

Dr Chris Barclay

• Bateman BT, Hernandez-Diaz S, Fischer MA et al. Statins and congenital malformations: cohort study.  BMJ 2015;350: h1035 doi: 10.1136/bmj.h1035