Night shift work in early pregnancy and risk of preterm birth among Dutch nurses in the Nightingale Study.

BACKGROUND

Working night shifts may influence hormonal balance and may increase risk of PTB.

AIMS: To assess the association between night shift work during early pregnancy and PTB risk in the Dutch Nightingale Study; a large cohort of (former) female nurses.

METHODS

The baseline cohort included 59 944 nurses, of whom 44 638 reported a first birth. Women reported lifetime reproductive and occupational histories in questionnaires in 2011 and 2017. Night shift work during pregnancy was classified as yes/no, number of nights worked per month and number of nights worked in a row per month. PTB was defined as early PTB (≥24-31+6 weeks of gestation) or late PTB (≥32-36+6 weeks) and PTB (<37 weeks) versus a term delivery (≥37 weeks). The association between night shift work and PTB risk was assessed in 44 638 nulliparous women using multivariable, multinomial logistic regression.

RESULTS

In total, 3197 (7%) women had experienced PTB. The risk of PTB was not associated with working night shifts (adjusted odds ratio (OR)=1.02, 95% confidence interval (CI)=0.94-1.11 for women who did compared to women who did not work night shifts), but women who worked night shifts during early pregnancy had lower risk of early PTB compared to women who did not work night shifts (adjusted OR = 0.75, 95% CI = 0.60-0.94).

CONCLUSIONS

This study among 44 638 nulliparous women found no association between working night shifts and risk of PTB. Contrary to earlier studies, we could adjust for PTB risk factors such as workload, maternal disease history and fertility treatment.