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Occup Environ Med. 2019 May;76(5):302-308. doi: 10.1136/oemed-2018-105592. Epub 2019 Mar 25.

Night work and miscarriage: a Danish nationwide register-based cohort study.

Author information

1
Department of Occupational and Evironmental Medicine, Bispebjerg and Frederiksberg Hospital, Copenhagen, Denmark.
2
The Parker Institute, Bispebjerg and Frederiksberg Hospital, Frederiksberg, Denmark.
3
National Research Centre for the Working Environment, Copenhagen, Denmark.
4
Institute of Cancer Epidemiology, Danish Cancer Society, Copenhagen, Denmark.
5
Department of Public Health, University of Copenhagen, Copenhagen, Denmark.
6
Department of Occupational Medicine, Danish Ramazzini Centre, Aarhus University Hospital, Aarhus, Denmark.

Abstract

OBJECTIVE:

Observational studies indicate an association between working nights and miscarriage, but inaccurate exposure assessment precludes causal inference. Using payroll data with exact and prospective measurement of night work, the objective was to investigate whether working night shifts during pregnancy increases the risk of miscarriage.

METHODS:

A cohort of 22 744 pregnant women was identified by linking the Danish Working Hour Database (DWHD), which holds payroll data on all Danish public hospital employees, with Danish national registers on births and admissions to hospitals (miscarriage). The risk of miscarriage during pregnancy weeks 4-22 according to measures of night work was analysed using Cox regression with time-varying exposure adjusted for a fixed set of potential confounders.

RESULTS:

In total 377 896 pregnancy weeks (average 19.7) were available for follow-up. Women who had two or more night shifts the previous week had an increased risk of miscarriage after pregnancy week 8 (HR 1.32 (95% CI 1.07 to 1.62) compared with women, who did not work night shifts. The cumulated number of night shifts during pregnancy weeks 3-21 increased the risk of miscarriages in a dose-dependent pattern.

CONCLUSIONS:

The study corroborates earlier findings that night work during pregnancy may confer an increased risk of miscarriage and indicates a lowest observed threshold level of two night shifts per week.

KEYWORDS:

cohort study; miscarriage; night work; payroll data; pregnancy

PMID:
30910992
DOI:
10.1136/oemed-2018-105592

Conflict of interest statement

Competing interests: None declared.

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