Clonazepam and other benzodiazepines have been associated with fetal damage, including congenital malformations, when taken by pregnant women in their first trimester. Clonazepam is best avoided in the first trimester and probably throughout pregnancy.

Source: http://www.medicinenet.com

Benzodiazepines are secreted in breast milk. Mothers who are breastfeeding should not take clonazepam. Reference: FDA Prescribing Information

Source: http://www.medicinenet.com