Pregnant women will undergo breath tests to check if they smoke under tough new measures to reduce the risks to hundreds of unborn children every year.

The Whittington Hospital, in Archway, will carry out screening on expectant mums using carbon monoxide (CO) monitors as part of its standard antenatal checks from this summer.

Women can choose to opt-out of the test, but otherwise the monitor will detect if they smoke or if they are affected by secondary smoking by a partner.

It comes as a Gazette investigation has found the health of 293 unborn babies in Islington was put at risk from maternal smoking from April 2013 to December 2014.

Consultant midwife Logan Van Lessen, who is spearheading the six-month pilot study at the Whittington, in Magdala Avenue, said: “We’ll offer CO monitoring to pregnant women who come in early pregnancy. We’ll do their screening and if they trigger above a certain level they will be offered no-smoking services.

“We don’t want to alienate people. But there are so many risks from smoking in pregnancy – miscarriage, stillbirth, ectopic pregnancy, premature birth and low birth weight. That’s why screening is important.”

Maternal smoking can seriously harm the unborn baby and it is hoped CO monitoring will encourage more women to seek professional help to quit.

We analysed Department of Health data for 200,000 pregnancies in London from April 2013 to December 2014 and found the majority of boroughs now have a maternal smoking rate below 10pc – compared to the England average of 11.7pc. In Islington the rate is 5.8pc but still above neighbouring Haringey where the rate is 4.7pc, Camden where it is 4.5pc and City and Hackney with 4.9pc.

But 1,562 expectant mums still smoked in these boroughs over this time.

Journalist Nathalie Raffray, of Croftdown Road, Dartmouth Park, smoked while pregnant with her son in 2002.

She said: “When I found out I was pregnant I gave up because I knew smoking was bad for the baby and I was on 20 Marlborough a day. But three weeks later it all collapsed and I started again. I moved onto rollies so I would smoke less, about five or six a day.

“So I was a pregnant smoker and all that came with it. If you’re there with your bump and a cigarette in your hand you will get vicious looks and snide comments.

“I did try to give up, especially after he was born, but it was really hard. You need that support.”

She eventually quit in 2011 and believes breath tests in early pregnancy may help others to seek help.

“As long as these checks aren’t invasive then I think it is a good idea,” she said. “It might shock people into giving up.”

Hazel Cheeseman, director of policy at public health charity ASH (Action on Smoking and Health), described the rates of maternal smoking as “concerning” and called on women to take the hard step of seeking support.

She said: “Giving up smoking while pregnant is one of the biggest things people can do to ensure their baby is healthy. If you smoke when you are pregnant the inequalities for that child begin before they are even born.”

Figures from ASH show up to 2,200 premature births and 5,000 miscarriages every year in the UK are caused by maternal smoking.

ASH said the low smoking rate among pregnant women in the capital was due to factors such as a high proportion of women from ethnic groups, where smoking is not prevalent, and women becoming pregnant when older than elsewhere in the country.

Traditionally places in the north of England have had the worst figures. The latest stats showed NHS Scarborough had 26.3pc of mothers-to-be smoking at full term.

For help to quit smoking call 0800 093 9030 or visit www.smokefreeislington.nhs.uk