Miscarriage, also known as spontaneous abortion and pregnancy loss; is the natural death of an embryo or fetus before it is able to survive independently. Some use the cutoff of 20 weeks of gestation; after which fetal death is known as a stillbirth. The most common symptom of a miscarriage is vaginal bleeding with or without pain. Sadness, anxiety, and guilt often occur afterwards. Tissue and clot-like material may leave the uterus and pass through and out of the vagina. When a woman keeps having miscarriages; infertility is present.

The greater risk of miscarriage

Working two or more night shifts in a week may increase a pregnant woman’s risk of miscarriage the following week by around a third, shows a prospective study published online in Occupational & Environmental Medicine. Previous studies have suggested that pregnant women face a greater risk of miscarriage if they work night shifts, but they have based on self-reported shift work and have not quantified the level; of increased risk or the amount of shift work involved.
For this study, the authors accessed payroll data on 22,744 pregnant women working in public services; mainly hospitals, in Denmark, and linked that with data from Danish national registers on births and admissions to hospital for the miscarriage to determine how the risk of miscarriage between weeks 4-22 of pregnancy was influenced by night work.
Overall 377,896 pregnancy weeks included an average of 19.7 weeks per woman. After week eight of pregnancy; women who had worked two or more night shifts the previous week had a 32% higher risk of miscarriage compared with women who had not worked any night shifts that week. And the risk of miscarriage increased with the number of night shifts worked per week and also by numbers of consecutive night shifts.

Abnormal fetuses with a gestational age

The association between night work and the risk of miscarriages was stronger after pregnancy in week 8. “This may explained by the decline in the proportion of chromosomally abnormal fetuses with gestational age; which makes an association with environmental exposure more easily detectable among later miscarriages,” the authors say. This is an observational study, and as such, can’t establish cause, and the authors point out that data on miscarriages, particularly early miscarriages, were incomplete.

But, as around 14% of women in Europe report working at night at least once a month; the findings have relevance for working pregnant women as well as their employers, physicians, and midwives, they emphasize. “Moreover, the results could have implications for national occupational health regulations.”

In terms of the underlying mechanism responsible for the association; women working night shifts are to light at night which disrupts their circadian rhythm and decreases the release of melatonin. Melatonin has been shown to important in maintaining a successful pregnancy; possibly by preserving the function of the placenta.