[Why are babies born at night at increased risk of early neonatal mortality?]

Increased perinatal and neonatal mortality rates have been previously reported in night-time births compared with births during the day. This effect has been attributed to decreased quality of medical care during the night. However, alternative explanations exist such as decreased birth-weight of night births. The objective of this study was to further investigate this relationship.

Data from 590,332 low risk births (singleton births, > or = 2500 g birth-weight, no major congenital anomaly) were obtained from the perinatal birth register of Hesse, Germany, 1990-2000. Outcome was defined as either death during labour or within 7 days of life. Night-time births were defined as births between 9.00 p.m. and 6.59 a.m., otherwise day-time births were assumed. Subgroup analyses and logistic regression analyses were performed to assess whether the excess mortality of night-births might be explained by other factors.

Mortality rates were increased in night-time births (RR = 1.26; 95% CI = 0.94-1.70). This relationship was more pronounced in spontaneous births (RR = 1.58; 95% CI = 0.96-2.61) and emergency cesarean sections (RR = 1.76; 95% CI = 1.10-2.82). Significance persisted after adjusting for numerous potential confounders.

Our results confirm an increased mortality risk for night-time births which could not be explained by other accessible risk factors. This suggests that the increased risk at night might be attributable to a reduced availability to provide appropriate medical care in delivery units at night.

As mainly the presence of staff is decreased during the night, introduction of better designed shifts can be expected to reduce neonatal mortality.