Night shifts in pregnancy tied to higher risk of child development concerns at age 4

Working night shifts during pregnancy is linked to a heightened risk of neurodevelopmental abnormalities detected by screening in the child by the age of 4, according to research published online in Occupational & Environmental Medicine. The findings also suggest, in an exploratory analysis, that the length of a mother’s nightly sleep during pregnancy may modify this observed association.

Night shift work during pregnancy has previously been associated with unfavourable health outcomes for both mother and child, including neurodevelopmental issues, potentially related to disturbances of the body clock and sleep. The researchers therefore set out to explore the associations between mothers’ night shift work and their children’s neurodevelopment, and to find out whether potentially modifiable prenatal factors, such as changes in night shift patterns and sleep duration, might play a role.

The team drew on nationwide survey data for around 100,000 pregnant women from the Japan Environment and Children’s Study (JECS), who were enrolled between January 2011 and March 2014. The women were surveyed in the first trimester and again in the second or third trimester, and answered questions about the number of night shifts they worked in a month. Their responses were divided into three groups: no night shifts reported in either survey (27,655 women); night shifts in the first but not the second survey, described as discontinued night shifts (1,779 women); and night shifts in both surveys, described as continued night shifts (2,084 women).

Prenatal sleep length was calculated from self-reported bedtime and wake-up times in the second or third trimester, and categorised as short if less than 6 hours, moderate if 6 to 9 hours, and long if 10 or more hours. Child neurodevelopmental abnormalities at age 4 were assessed using a developmental screening tool, the Japanese version of the Ages and Stages Questionnaire, Third Edition (J-ASQ-3). This screening instrument covers five domains: communication; gross motor skills; fine motor skills, meaning the ability to make small, precise, deliberate movements; problem solving; and personal-social functioning, which covers interpersonal skills, emotional and behavioural development, and awareness of personal boundary and space.

In all, 31,528 mothers who worked in the first trimester and completed the child development questionnaire when their children were 4 years old were included in the analysis. Some 4,189 children, just over 13 percent, were classified as high risk of an abnormality in at least one of the five J-ASQ-3 domains: 1,210 (4 percent) for communication; 1,599 (5 percent) for gross motor skills; 1,906 (6 percent) for fine motor skills; 913 (3 percent) for problem solving; and 1,495 (5 percent) for personal-social functioning.

Compared with the children of mothers who did not work night shifts, the children of those who discontinued night shift work were more likely to have developmental screening abnormalities, but only in the fine motor skills domain, where the risk was 24 percent higher. The children of mothers who continued night shifts throughout their pregnancy had higher risks in three domains compared with children whose mothers did not work night shifts: communication skills (29 percent higher risk), fine motor skills (34 percent higher risk) and personal-social functioning (31 percent higher risk). Only the fine motor skills domain showed a significant association regardless of whether night shifts were continued or discontinued.

“One possible explanation is that maternal inflammation associated with persistent night work may preferentially affect neural pathways involved in fine motor function,” suggest the researchers. A separate exploratory analysis showed that the observed association between night shift pattern and the child’s neurodevelopmental risk differed according to how long the mothers slept. Prenatal sleep duration of 10 or more hours was associated with an 80 percent heightened risk of abnormalities in any of the five domains compared with a prenatal sleep length of 6 to 9 hours. The researchers note that long prenatal sleep duration may also reflect underlying fatigue, subclinical depression, inflammation or anaemia, rather than representing a harmful exposure in itself.

This is an observational study, and as such it cannot establish cause and effect. The researchers also acknowledge that they were not able to account for shift rotation systems, individual chronotype, workload, exposure to light, or the timing of night shift discontinuation, all of which might have influenced the findings. Nevertheless, in light of the results, they suggest it may be worth employers considering flexible work schedules for pregnant night shift workers.

Subject of Research: Maternal night shift work during pregnancy and child neurodevelopmental screening outcomes at age 4

Article Title: Night shifts during pregnancy linked to heightened risk of young child’s neurodevelopmental abnormalities

Article References: Night shifts during pregnancy linked to heightened risk of young child’s neurodevelopmental abnormalities. Original publication (Bibliographic details unavailable.)

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DOI: Not provided

Keywords: night shifts, pregnancy, neurodevelopment, child development, sleep duration, fine motor skills, observational study, Japan Environment and Children's Study, occupational health, J-ASQ-3, circadian rhythm, BMJ Group