The objective of the study was to evaluate the possible association between maternal acute respiratory infectious diseases (ARID) during pregnancy and birth outcomes. Newborn infants born to mothers with or without ARID as reference were compared in the population-based large data set of newborns without any defect in the Hungarian Case-Control Surveillance System of Congenital Abnormalities. Main outcome measures were birth weight and gestational age at delivery, in addition the rate of preterm births and low birthweight newborns. Of 38,151 newborns, 3,455 (9.1%) had mothers with ARID during pregnancy which were differentiated according to six manifestations from sinusitis to the pneumonia. Mothers with ARID in pregnancy had a longer (0.3 week) gestational age at delivery (adjusted t = 5.4; p < 0.0001) and a lower rate of preterm births (6.7% vs. 9.4%) [adjusted odds ratio (OR) with 95% confidence interval (CI): 0.72, 0.63-0.83] than mothers without ARID. However, severe ARID (bronchitis-bronchiolitis and particularly pneumonia) associated with a higher rate of preterm births (13.0%, adjusted OR with 95% CI: 1.4, 1.1-1.8), while mild ARID (sinusitis, pharyngitis, tonsillitis, laryngitis-tracheitis) resulted in a lower rate of preterm births (5.5%, adjusted OR with 95% CI: 0.5, 0.4-0.7). In conclusion, there was an obvious correlation between severity of ARID in pregnant women and rate of preterm births.