Standing for long periods of time when pregnant may slow foetal growth, a study suggests.
Researchers found that women who stood for the majority of time at work had babies whose heads were around 1cm smaller than average.
This did not affect the health of the babies at birth.
The work, published in the journal Occupational and Environmental Medicine, followed 4,680 mothers throughout their pregnancies.
Around four out of ten of these women had jobs where they spent around eight hours on their feet - such as hairdressing, sales and working with toddlers.
Prof Alex Burdorf, the lead author, said: "While previous studies have looked at how standing for long periods of time may affect birth weight and delay birth - this is the first study to look at the effects on foetal growth.
"We were not surprised that head size was smaller in pregnant women who stand for a long time at work, but we were pleasantly surprised to find that it was only by a modest amount - 3% smaller than average at birth."
Baby head size
Tim Overton from the Royal College of Obstetricians and Gynaecologists said: "It is very difficult to say if the finding in this study is clinically significant. To see if head size has an affect on the babies' neuro development you would have to follow them for many years as they grow up.
"There have been studies before that show women who work hard in pregnancy seem to run a higher risk of giving birth to smaller babies. But there is no evidence that this is significant in the long-term health of these babies."
The study also showed that working up to 36 weeks of pregnancy had no impact on birth weight, size or prematurity.
Nor did work involving heavy lifting - which is contrary to other studies that have suggested physical work can adversely affect pregnancy, including increasing the risk of pre-term delivery.
