Breath-test pregnant women to see if they smoke, study suggests

Women who hide habit miss out on vital monitoring and have more issues, study shows

Pregnant women should be breath-tested during antenatal visits to check whether they are smoking, a new Irish study suggests.

Women who hide their smoking habit miss out on vital monitoring of their pregnancy and end up having more problems as a result, according to the study of women attending the Coombe hospital in Dublin.

It found a substantial number of women with high carbon monoxide levels – an indicator of smoking – had not declared their tobacco use.

An increased level of breath carbon monoxide (BCO) was associated with lower birth weight of babies and an increased risk of adverse pregnancy and neonatal outcomes, results showed.


The authors, from the Coombe and University College Dublin, said this finding strengthens the case for universal BCO screening at the first antenatal visit. A high reading should result in referral of the woman to smoking cessation services and close monitoring of the baby, they say.

Likening the test to the alcohol breathalyser used by the Garda, co-author Prof Michael Turner of UCD’s centre for human reproduction said it was “quick, painless and costs less than a cigarette”.

Adverse events

Women with high BCO levels had babies that were smaller as well as an almost two-fold rate of having two or more adverse pregnancy events, the study found.

Of the 234 women whose data was analysed, 43 per cent said they had never smoked, 40 per cent reported they were ex-smokers and 17 per cent reported currently smoking to midwives.

In addition to those who said they smoked, analysis of questionnaires and breath tests showed another 10 per cent had high BCO readings.

“Although a proportion of women categorised as ‘non-disclosers’ may be ‘false-positive’, the results of this study indicate that non-disclosers have poor pregnancy outcomes compared with verified non-smokers in early pregnancy,” the study says.

These “non-disclosers” tended to be better educated than those who admitted smoking, according to Prof Turner. “They know it’s something they shouldn’t be doing but are reluctant to disclose. Yet they may have a baby whose growth is restricted and risk an adverse outcome.”

Women who fail to disclose their smoking do not get the level of monitoring during pregnancy they actually require, the study, published in the European Journal of Obstetrics & Gynecology and Reproductive Biology, points out.

Paul Cullen

Paul Cullen

Paul Cullen is a former heath editor of The Irish Times.