Pregnant Kiwi women are reluctant to step on the scales, leading to underestimated BMI measurements and misguided clinical care, research shows.
Two related studies, published in the New Zealand Medical Journal today, found weighing of pregnant women was no longer common practice for midwives.
This resulted in underestimated BMI measurements during pregnancy, which could affect clinical care, the researchers said.
Consultant obstetrician and gynaecologist and senior lecturer, Dr Helen Paterson, who was an author of both studies, said midwives found weight to be a sensitive issue with pregnant women. Discussion around it could offend the women.
"Weight is a sensitive topic in our society," Paterson said.
"We need to be talking about it more and recognising the importance of weight in pregnancy."
The study found the most common method for midwives obtaining a baseline BMI was to use a woman's self-reported height and weight.
This was problematic, as women were found on average to underestimate their weight.
Researchers compared the height and weight of 248 pregnant women recorded at a prenatal screening scan with the women's actual height and weight, and found about 70 per cent of the women had an under-reported BMI.
"You wouldn't ask me to guess your blood pressure," Paterson said.
"Weight is just a health measure, and for me to provide you with care, I need to know what it is."
Inaccuracies in recording weight and height during pregnancy could affect maternity carers' advice and clinical care, she said.
The research found heavier women were more likely to have an under-reported weight, which could lead to "unnecessarily increased risk in pregnancy".
Excess weight gain during gestation was linked with increased risk for abnormally high blood pressure, diabetes, complications during labour and delivery, and obesity.
"Even women who are of normal weight are affected," Paterson said.
"If you're under-reporting weight by 10 kilograms, or even five kilos, you could give that woman an inaccurate risk assessment."
The research recommended creation of New Zealand guidelines for the management of gestational weight gain to help close the gap between knowledge and practice.
It said BMI should be calculated as part of routine clinical practice.
Paterson said it was a conversation that needed to happen, in the interest of mothers and their babies.
"If you go back 20 years, [measuring weight and height] was normal," she said.
"Society needs to start normalising measuring weight and height in pregnancy again."
Both studies were funded by the University of Otago.
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