Observational Cohort Links Continued Night Shifts in Pregnancy to 34% Higher Fine-Motor Screening Risk at Age 4

The analysis divided participants into no night shifts, discontinued after first trimester, and continued night shifts, then scored five developmental domains with the Japanese Ages and Stages Questionnaire. Absolute prevalence of any domain abnormality reached 13.3%; continued night shifts raised communication, fine-motor, and personal-social risks by 29%, 34%, and 31% respectively, while only fine-motor risk remained elevated after discontinuation. Sleep duration modified the pattern, with ≥10 h prenatal sleep linked to 80% higher any-domain risk. Prior Scandinavian registry studies have reported similar motor-domain signals but lacked trimester-specific exposure data. The JECS design cannot separate night-shift effects from unmeasured socioeconomic or inflammatory confounders. A next-step study requires prospective actigraphy plus inflammatory biomarkers in a multi-country cohort to test mediation.