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Clonazepam use in pregnancy and the risk of malformations.

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Genetics and Teratology Unit, MassGeneral Hospital for Children, Boston, Massachusetts 02114, USA.



Clonazepam (Klonopin) is a benzodiazepine that has been used widely to treat seizures and conditions such as panic attacks and anxiety disorder. However, the current findings about its use in pregnancy are derived from limited studies of small sample size. Because it is commonly prescribed during pregnancy, more information about its safety is needed.


The medical records of 28,565 infants were surveyed as part of a hospital-based malformation surveillance program to identify those who had been exposed prenatally to an anticonvulsant, including clonazepam.


During a 32-month period, 166 anticonvulsant-exposed infants were identified; 52 had been exposed to clonazepam, 43 as monotherapy. A total of 33 (76.7%) of the monotherapy infants were exposed during the first trimester. One (3.0%) infant had dysmorphic features, growth retardation, and a heart malformation (tetralogy of Fallot).


This study did not observe an increase in major malformations in births exposed to clonazepam monotherapy. However, this study is not large enough to have adequate power to determine whether or not the rate of major malformations is increased in clonazepam-exposed pregnancies. No increase has been identified in three other case series. Although the number of patients in this series was larger than previous reports, continued monitoring of pregnancies is needed to determine whether or not clonazepam is teratogenic.

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