A new Danish study found each extra hour of bending forward at work during early pregnancy raised the risk of miscarriage by 36%.
It also found each extra hour of walking per day increased the risk of miscarriage by 18% and each hour of standing increased it by 3%.
If you’re pregnant and have a physical job, or are trying to follow the advice to stay active, these results might be alarming and seem at odds with the usual advice to stay active.
But most miscarriages have nothing to do with what a woman did or didn’t do.
Let’s have a closer look at what the study investigated and found, and what this actually means for women who are pregnant or planning a pregnancy.
What the researchers did
The Danish researchers used national health and employment records to track more than 800,000 pregnancies between 2004 and 2018.
They matched each woman’s job title to a database that estimates the amount of standing, walking and bending in that line of work. They didn’t ask women what they did at work.
The database itself was built from motion sensors 403 pregnant Danish workers wore, along with expert ratings for every job.
The researches then statistically analysed the difference in the risk of miscarriage, based on the activity that may be required for each occupation.
What they found
Just over one in ten pregnancies in the study resulted in miscarriage.
Of the three activities, forward bending showed the clearest association with miscarriage, with a 36% increased risk of miscarriage for each extra hour of bending per day.
Standing had little effect, with a 3% increased risk for each hour per day spent standing. This effect almost vanished once the researchers attempted to account for smoking status.
Walking sat somewhere between the two, with an 18% increased risk.
But walking at work does not automatically push your miscarriage risk up by 18%. The figure applies only to each additional hour per day added to the baseline rate. The same applies to bending and standing.
The baseline amounts of bending in the study were smaller than you’d expect. The typical worker bent forward for about 24 minutes across an eight-hour shift.
If your baseline miscarriage risk is around ten in 100, an extra hour of bending above that period each day might lift it to about 13 in 100.
What the study didn’t do
The study has some real blind spots: the biggest is smoking. Nearly 10% of women in the most physically demanding jobs smoked during pregnancy, against about 4% in the least physically demanding jobs.
While researchers attempted to adjust for this important variable, they were only partially successful. Smoking is one of the strongest risk factors for miscarriage, and the researchers had no individual smoking data for most of the women in the study.
There is also nothing in the data on body weight, thyroid dysfunction, diabetes, mental health or fertility treatment, all of which affect miscarriage risk .
Forward-bending also tends to go hand in hand with heavy lifting, which other research has more clearly tied to miscarriage. The Danish team could not separate the two. And oddly, women in the very highest-exposure jobs didn’t actually have the highest risk of miscarriage.
If physical work were really the main driver, you would expect the opposite.
What has other research found about the causes?
Most miscarriages have nothing to do with what a woman did or didn’t do. The most common cause is a random genetic mutation in the fetus, which the body then recognises and lets go of.
The risk of such an abnormality increases with women’s age, especially after about 35. A large Norwegian study found about one in ten pregnancies miscarried at age 25, rising to more than one in two by age 45.
Smoking, heavy drinking, very high or low body weight, uncontrolled diabetes or thyroid disease, and some infections, also play a role. Previous miscarriages also raise the risk , as does stress, being aged under 20, working night shifts, air pollution and exposure to pesticides.
Don’t stop walking
The benefits of staying active in pregnancy are well established. Regular walking and moderate exercise lower the risk of gestational diabetes, excessive weight gain, high blood pressure and depression.
Australian guidelines recommend 150 to 300 minutes of moderate activity a week through pregnancy, unless your doctor says otherwise.
The Danish paper looked at hours of standing or walking on a hard floor at work. A 30-minute walk around the block is a totally different thing.
What this all means if you’re pregnant
If your job involves a lot of bending – in professions and industries such as aged care, nursing, cleaning, hairdressing or stacking shelves – it’s reasonable to ask your employer about adjusting duties, including in the first trimester.
This might include:
- sitting breaks
- a stool for tasks that don’t really need standing
- swapping the heaviest jobs with a colleague
- wearing comfortable footwear.
If you’ve recently had a miscarriage, chances are it was caused by a genetic abnormality of an embryo and in most cases, nothing could have been done to prevent it.
The evidence is nowhere near strong enough to support a casual link between physical activity at work and the risk of miscarriage. The vast majority of miscarriages would have happened, whatever you were doing.
