To the Editor: Antibiotics administered to mother close to delivery of the neonate could protect both mother and neonate from infection or result in adverse outcomes [1, 2]. Antibiotics are known to affect the maternal microbiome, and might affect the developing microbiome in neonates [3, 4]. We retrospectively assessed the effect of systemic antibiotics other than surgical prophylaxis given to mothers within a week prior to delivery, on necrotizing enterocolitis (NEC), sepsis or death in 200 preterm neonates born at 26+0- 36+6 wk of gestation. The primary outcome was a composite of NEC (Bell stage ≥II), culture-positive sepsis or death prior to discharge. Institutional ethics approval was obtained with waiver of consent.

Mothers of 77 neonates (38.5%) were exposed to antibiotics, most commonly ampicillin (11.7%) or erythromycin (10.7%). Among the neonates, 90 (45%) received antibiotics in the first 28 d of life. Common indications were suspected sepsis (76%) and culture-positive sepsis (23%). Amikacin (39%), ciprofloxacin (24%) and cefoperazone-sulbactam (19%) were prescribed most frequently. Three neonates developed NEC (1.5%), 24 had sepsis (12%), 27 died before discharge (13.5%), and 40 developed the composite outcome (20%). After adjusting for gestational age, male sex and receipt of prenatal steroids in a logistic regression model, maternal antibiotic exposure was associated with a decrease in the odds of the composite outcome (aOR 0.26, 95% CI 0.10–0.64). No significant association was seen with the individual outcomes of NEC, sepsis or death. Median duration of hospital stay was similar among the two groups.

An overall protective effect of maternal antibiotic exposure on neonatal outcomes was observed in this study after adjusting for key confounding factors. Our population was geographically limited, the data were retrospective, and we did not assess dysbiosis in the neonates. These findings, and long-term clinical and microbiological effects need to be assessed prospectively in future studies.