As few drugs are known to cross the placenta
and can have adverse effects in fetus.
Pregnancy may be complicated by new-onset or preexistent allergic disease, including rhinitis, anaphylaxis, urticaria and angioedema, and atopic dermatitis. Pregnancy and asthma is extensively studied.
Of the currently available preparations, chlorpheniramine has been recommended as the first generation antihistamine of choice for use during pregnancy.