Background: Low birthweight and major congenital malformations (MCMs) are key causes of infant mortality. Objectives: The aim of this study was to explore the prevalence of MCMs in infants with low and very low birthweight and analyze the impact of MCMs and birthweight on infant mortality. Methods: We determined prevalence and infant mortality of 28 life-threatening MCMs in very-low-birthweight (<1,500 g, VLBW), low-birthweight (1,500–2,499 g, LBW), or normal-birthweight (≥2,500 g, NBW) infants in a cohort of 2,727,002 infants born in Germany in 2006–2017, using de-identified administrative data of the largest statutory public health insurance system in Germany. Results: The rates of VLBW, LBW, and NBW infants studied were 1.3% (34,401), 4.0% (109,558), and 94.7% (2,583,043). MCMs affected 0.5% (13,563) infants, of whom >75% (10,316) had severe congenital heart disease. The prevalence (per 10,000) of any/cardiac MCM was increased in VLBW (286/176) and LBW (244/143), as compared to NBW infants (38/32). Infant mortality rates were significantly higher in infants with an MCM, as opposed to infants without an MCM, in each birthweight group (VLBW 28.5% vs. 11.5%, LBW 16.7% vs. 0.9%, and NBW 8.6% vs. 0.1%). For most MCMs, observed survival rates in VLBW and LBW infants were lower than expected, as calculated from survival rates of VLBW or LBW infants without an MCM, and NBW infants with an MCM. Conclusions: Infants with an MCM are more often born with LBW or VLBW, as opposed to infants without an MCM. Many MCMs carry significant excess mortality when occurring in VLBW or LBW infants.
