Women who do shift work during their pregnancies are at greater risk of having an underweight baby, a new study suggests.
Shift work that requires people to alternately work days and nights disrupts their body's internal clock, which in turn throws off sleep schedules and metabolism.
That's crucially important for pregnant women, whose blood sugar levels need to be stable in order for their developing babies to get adequate nutrition to grow to healthy sizes.
When researchers the University of
and South Australian Health and Medical Research Institute put pregnant sheep on the same waking and sleep schedule shift-working women might keep, they had smaller lambs.
Except, that is, when they were carrying twins. In this case they had longer pregnancies. The reasons and implications of that particular connection are unclear, but experts warn a consistent change in outcome shows shift work has a clear impact on pregnancy.
Shift work, it seems, is particularly stacked against women.
About one in five American employees work shifts, which could mean night shifts, rotating shifts or evening ones.
Even if you always work nights - rather than more irregular non-standard hours - this still keeps you from sleeping when the human body is meant to sleep.
Getting too little or poor quality sleep raises the risks of just about everything (including death) for just about everyone.
But women have it particularly bad.
Compared to women working odd shift, women are more likely to develop cancer.
Plus, they face double the risks of breast cancer that other women do.
Everything that happens to a woman's body during pregnancy has the potential to affect the fetus growing in her womb, too - including keeping odd hours.
Yet, in the US, there is on law requiring employers to make any accommodations for pregnant women.
To work out what effects continuing shift work might have on pregnant women, the Australian research team used sheep as a model, because the pregnant animals have similar blood system structures and nutrient exchange between mother and fetus to humans.
The scientists saw that sheep who were made to sleep and eat on a 'shift-work' schedule made pregnant sheep - like humans - more intolerant to gluten, a risk factor for diabetes and obesity later in life.
But not being able to properly process glucose may also prevent the essential blood sugars from being transferred to her fetus, resulting in a lower birth weight, they found.
Most previous work has looked at the effects of sleep quality during the later stages of pregnancy on a child's obesity risks later in life.
In the new research, published in the Journal of Physiology, the researchers found that even if a sheep was taken off the 'shift' schedule after her first trimester, her offspring were still more likely to be relatively small.
'The effects of shift work on pregnancy are not well understood. We found that exposure to rotating night and day shifts, even if only in pregnancy, altered both maternal metabolic and pregnancy outcomes,' said lead study author Dr Kathy Gatford, a reproductive health professor at the University of Adelaide.
Next, they will look into more specific concerns and for further down the line for both mothers and babies.
'We are now assessing whether maternal shift work affects the health of their children by looking at circadian rhythms, cardiometabolic health and body composition in the progeny in this study.'