Rejno G, et al. - This study assessed the role of measured and unmeasured confounding by familial factors on the associations between maternal asthma and adverse pregnancy and perinatal outcomes. For this purpose, differentially exposed cousins and siblings from the same families were compared. Findings revealed that the observed link between maternal asthma and adverse pregnancy outcomes was not seemed to be explained by the factors shared by siblings and cousins. This suggested that targeting the asthma disease will continue to be crucial in attenuating risks for adverse outcomes in pregnancy.