Night Shifts During Pregnancy Linked to Higher Developmental Screening Risks in Children at Age 4

A large Japanese birth cohort has produced a finding that will matter to anyone who works nights while pregnant: mothers who kept working night shifts through pregnancy had children who were more likely to be flagged on a developmental screening at age 4. The research was published online in Occupational & Environmental Medicine.

The data come from the Japan Environment and Children's Study, a nationwide survey of around 100,000 pregnant women enrolled between January 2011 and March 2014. Women were surveyed in the first trimester and again in the second or third, and each time were asked how many night shifts they worked in a month. The researchers wanted to know whether night work was tied to children's neurodevelopment, and whether factors that could be changed, such as shift patterns and sleep length, played a role. Earlier work had linked night shifts in pregnancy to poorer outcomes for mother and child, possibly through disruption of the body clock and sleep.

The analysis covered 31,528 mothers who were working in the first trimester and who completed a child development questionnaire when their children were 4. They fell into three groups: 27,655 who reported no night shifts in either survey; 1,779 who worked nights in the first survey but not the second, labelled the discontinued group; and 2,084 who reported night shifts in both, the continued group.

Children were assessed with the Japanese version of the Ages and Stages Questionnaire, Third Edition, a screening tool covering five domains: communication, gross motor skills, fine motor skills, problem solving, and personal-social functioning. Overall, 4,189 children, just over 13%, were classed as high risk in at least one domain. By domain, that was 1,210 (4%) for communication, 1,599 (5%) for gross motor, 1,906 (6%) for fine motor, 913 (3%) for problem solving and 1,495 (5%) for personal-social functioning.

Compared with children of mothers who did no night work, children of mothers who stopped night shifts had a 24% higher risk of screening abnormalities, but only in fine motor skills. Children of mothers who continued night shifts showed higher risk in three domains: communication, 29% higher; fine motor skills, 34% higher; and personal-social functioning, 31% higher. Fine motor skills was the only domain with a significant association whether night work was continued or discontinued. The authors suggest that maternal inflammation tied to persistent night work may preferentially affect neural pathways involved in fine motor function.

A separate exploratory analysis found the link between night shift pattern and child risk differed according to how long mothers slept. Prenatal sleep of 10 hours or more, measured from self-reported bedtime and wake-up times in the second or third trimester, was associated with an 80% higher risk of abnormalities in any of the five domains, compared with sleep of 6 to 9 hours. The researchers caution that long sleep may reflect fatigue, subclinical depression, inflammation or anaemia rather than being harmful itself.

The study is observational and cannot establish cause and effect. The authors say they could not account for shift rotation systems, individual chronotype, workload, light exposure, or when mothers stopped night work, any of which could have influenced the results. Even so, they say employers might consider flexible work schedules for pregnant night shift workers. The sleep findings are described as exploratory, so the open question is whether sleep and inflammation truly sit in the pathway.