Use during pregnancy is not recommended.
en.wikipedia.org/wiki/Doxycycline
Doxycycline crosses into breastmilk.
Other tetracycline antibiotics are contraindicated in pregnancy and up to eight years of age, due to the potential for disrupting bone and tooth development.
They include a class warning about staining of teeth and decreased development of dental enamel in children exposed to tetracyclines in utero, during breastfeeding or during young childhood.
However, the FDA has acknowledged that the actual risk of dental staining of primary teeth is undetermined for doxycycline specifically.
The best available evidence indicates that doxycycline has little or no effect on hypoplasia of dental enamel or on staining of teeth and the CDC recommends the use of doxycycline for treatment of Q fever and also for tick-borne rickettsial diseases in young children and others advocate for its use in malaria.
en.wikipedia.org/wiki/Doxycycline#Pregnancy_and_lactation
