Risks of smoking in pregnancy

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Why is smoking so harmful?

When someone smokes a cigarette they inhale over 4,000 different chemicals, none of which should be in their bodies. Some can cause damage that cannot changed or made better. Here are a few of those chemicals:
When tobacco is burnt a poisonous gas called Carbon Monoxide (CO) is produced. You cannot see, taste or smell this gas at all. It is thick and sticky and tends to linger in the air and blood stream for many hours. CO is not only produced from tobacco smoke but can also be found in car exhaust fumes, faulty gas appliances, wood burners and open fires. Therefore, a smoker and/or passive smoker will breathe in CO. An unborn baby receives all its nutrients and oxygen from the placenta. When a pregnant person smokes or is exposed to smoke, CO restricts oxygen and nutrients to the placenta which are essential for a baby’s healthy growth and development. Restricting a baby’s oxygen supply means that the baby’s heart has to work much harder to get enough oxygen into their bloodstream.

Checking CO levels at midwifery appointments

During every planned antenatal appointment, your midwife will perform screening to check CO levels. Your midwife will ask you to blow into a hand-held machine, called a CO monitor, which measures the level of carbon monoxide in your body. These levels indicate how much CO is in the bloodstream and guides health professionals to provide the appropriate care and support required.

What is passive smoking?

It is not just smoke from the pregnant person that can affect a baby’s health and development; it is second and third-hand smoke from other people too. When people smoke, most of the smoke goes into the surrounding air where anyone close by can breathe it in (second-hand smoke). People who regularly breathe in second-hand smoke can suffer the same health problems as those people who actually smoke.
Third-hand smoke is what’s left behind when someone smokes. It’s what you smell on things like clothes, furniture, carpets, walls, skin and hair that’s been in or around smoke. Third-hand smoke sticks to these things, builds up over time and is hard to remove which is why smoking in another room still poses potential harm and opening windows does not really help. Both second and third-hand smoke can have the same impact on an unborn baby. This is why your maternity team want to support everyone in your household to become smoke free and give your baby the best start in life.

Second-hand Smoke in the home

There is no safe level of exposure to second-hand smoke. Children are particularly vulnerable to second-hand smoke. Most of their exposure occurs in the home.

Children who live with a smoker are about twice as likely to become smokers themselves.

Heating, air conditioning and ventilation systems cannot eliminate exposure to second-hand smoke.

Opening windows and using fans does not completely remove second-hand smoke.

Second-hand smoke can travel through doorways, cracks in walls, ventilation systems and plumbing

The effects of smoking in pregnancy

CO restricts a baby’s oxygen supply and every cigarette smoked reduces the oxygen supply for 20-30 minutes. This lack of oxygen weakens the placenta considerably, which increases the chance of miscarriage. It can cause placental abruption, where the placenta separates from the uterus. This is life-threatening to the baby and pregnant person. It can also cause placental insufficiency, which affects the baby’s development and growth. These babies can be smaller in size which means they are struggling to grow as they are not receiving enough oxygen and nutrients. If babies do not grow well due to placental insufficiency, they are more at risk of being born early, requiring more care during the pregnancy and being stillborn. This table shows the level of risk of being a pregnant smoker and being exposed to second-hand smoke:
Maternal smokingSecond-hand smoke exposure
Low birth weight2 times more likelyAverage 30-40g lighte
Heart defects25% more likelyIncreased risk
Stillbirth47% more likelyPossible increase
Preterm birth27% more likelyPossible increase
Miscarriage32% more likelyIncreased risk
Sudden infant death3 times more likely45% more likely

How smoking in pregnancy affects labour and birth

When a pregnant person smokes this can have an impact on them, the birth and the baby during childbirth.
RisksEffects
BleedingHeavier bleeding or significant haemorrhage
Raised blood pressureAdds complications to your pregnancy and birth, reduces your birth choices and may mean you need medication
Induction of LabourIncreased interventions needed during birth
Restricted growthBaby less likely to cope with the birth – emergency caesarean
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