Night shifts through pregnancy tied to more child screening flags

Clinical takeaway: Ask pregnant patients who work nights about their schedule. Children whose mothers kept working nights appear more likely to screen positive for a developmental concern at age four, but not overall when mothers stopped by the second or third trimester. 

Night work is routine in nursing and other round-the-clock fields. Evidence on those shifts has centered on pregnancy loss, preterm birth, and metabolic outcomes in children. Child neurodevelopment has had limited data. This prospective birth cohort extends the evidence to developmental screening at age four, and it separates mothers who continued night shifts from those who stopped. 

On the age-four screening questionnaire that caregivers completed, children whose mothers continued night shifts through pregnancy were 27% more likely than children of mothers with no night shifts to score in the high-risk range in at least one of five developmental domains. About 13% of all children did, and the absolute differences between groups were modest. By domain, the high-risk range turned up 34% more often for fine motor skills, 31% for personal-social functioning, and 29% for communication. Gross motor (25%) and problem-solving (30%) screens ran in the same direction, though both plausible ranges included no difference. 

Mothers who stopped night shifts between the first and second or third trimester had children with no clearly elevated rate of high-risk screens overall: the rate ran 9% above the no-night-shift group, within a plausible range that included no difference. Fine motor screens were the exception, 24% above the no-night-shift group and the only domain with a clear elevation in both groups. Communication, gross motor, problem-solving, and personal-social screens were not clearly elevated after stopping night-shift work. The paper did not compare the stopped and continued groups directly. 

The analysis drew on the Japan Environment and Children’s Study, a nationwide prospective birth cohort. It followed 31,528 mothers who worked during the first trimester and compared those who continued, stopped, or never worked night shifts. Night shifts were self-reported, outcomes came from caregiver questionnaires rather than clinical diagnosis, and the timing of stopping was not measured. 

The authors call for studies that pin down when in pregnancy night work matters and which shift conditions drive the association. The cohort did not capture rotation patterns, workload, light exposure, or chronotype, so those are the next variables to test. Workplace schedule flexibility for pregnant night workers might merit consideration in the meantime, they argue. 

“One possible explanation is that maternal inflammation associated with persistent night work may preferentially affect neural pathways involved in fine motor function,” the authors suggest. They add that the mechanism remains speculative in this study. 

Source: Ikeda S, et al. (2026 Oct 27) Occup Environ Med. Maternal night shift patterns during pregnancy and offspring’s development at 4 years of age: the Japan Environment and Children’s Study