By MARTIN JOHNSTON
Untreated asthma in pregnant women increases the risk of their boys dying before birth.
Girl foetuses respond differently to the disease: their growth tends to be restricted. But if their mothers use inhaled steroid medicine to prevent asthma symptoms, the girls' growth keeps up with the boys'.
These are among the findings of an Australian research team, presented in Queenstown yesterday at the Medical Sciences Congress.
It was one of many papers to look at foetal growth. Several made connections between under-nutrition in the womb and diseases in adulthood such as heart and diabetes.
About 15 per cent of New Zealanders have asthma.
Dr Vicki Clifton, of the Hunter Medical Research Institute in New South Wales, said that among asthmatic women who had unexplained stillbirths at Hunter Hospital, 93 per cent of the foetuses were boys. But among women without asthma, the figure was 51 per cent.
"We're trying to work out why female babies decrease growth and survive while male babies put themselves at risk of a poor outcome by continuing growing.
"The female baby adjusts how her placenta works, to cope with the presence of the mother's asthma. The male baby doesn't make many changes and keeps growing on."
The difference was related to the way boy and girl foetuses processed glucocorticoids, natural steroids involved in foetal growth and the development of the central nervous and cardiovascular systems.
"Female and male babies have different ways of controlling those pathways, not only in asthmatic pregnancies, but in normal pregnancies."
Dr Clifton said the mothers' use of inhaled glucocorticoid-steroid medicine did not affect foetal growth; rather it was the drugs' role in preventing symptoms that was important.
The findings might have implications for the practice of giving glucocorticoid drugs to women at risk of giving birth prematurely. The drugs are given to speed development of the foetus' lungs.
But Dr Clifton said the research had further to go before recommendations could be made on setting the dosage depending on the foetus' sex.
