Doxycycline itself is unlikely associated with an increased risk of congenital malformations, reduced fetal bone growth or teeth staining with in utero exposure, however, is usually avoided during pregnancy because of the associations of these adverse events with other tetracyclines (particularly in the second and third trimester).
Tetracyclines might induce hepatic necrosis in some pregnant women, however, this is a rare syndrome most commonly associated with intravenous dosing of tetracyclines.
Doxycycline can be used during breastfeeding for short courses (ie. up to 3 weeks) as this has not been associated with infant dental staining.
Longer courses (ie. greater than 3 weeks) or repeat courses should be avoided as a precaution.