For a study, the researchers sought to assess the safety of allergen-specific immunotherapy (AIT) during pregnancy, particularly the risk of congenital abnormalities. Between 2005 and 2014, the Medical Birth Register and the Prescribed Drug Register were used to identify pregnancies exposed to AIT, both subcutaneously and sublingually. The National Patient Register provided information on congenital abnormalities in progeny. Investigators linked data from different registers using the personal identity number. After controlling for potential confounders, they derived odds ratios (ORs) with 95% CIs for congenital malformations and other poor pregnancy outcomes using logistic regression. The study group found 924,790 singleton pregnancies between 2005 and 2014. About 743 pregnancies were exposed to AIT from 3 months before conception to week 22 of pregnancy. Congenital malformations (OR=0.90; 95% CI, 0.63-1.27) or other adverse pregnancy outcomes (preterm birth: OR=0.98; 95% CI, 0.71-1.35; stillbirth: OR=0.79; 95% CI, 0.26-2.47; or caesarean delivery: OR=0.91; 95% CI, 0.76-1.09) were not linked to allergen-specific immunotherapy in pregnancy. The ORs were identical whether the immunotherapy was given subcutaneously or sublingually. The results were comparable when the pregnancy cohort was restricted to women with asthma or pulmonary disease, nulliparous women, and births from 2012 to 2014. According to this statewide investigation, there was no evidence of congenital abnormalities or other negative pregnancy outcomes in women who received AIT throughout pregnancy.