Dr Mark Rosenthal

MD MB ChB FRCP FRCPCH BSc

Consultant in Paediatric Respiratory Medicine

also specialist in Food Allergies & Disorders of Sleep

A | A | A

T: 0207 351 8832

E: s.harvey@rbht.nhs.uk

A:The Royal Brompton Hospital, London, SW3 6NP

Are Viral Infections Common in Babies Whose Mothers Smoked During Pregnancy?

If you’re a smoker there are lots of good reasons to try and quit. If you’re hoping to get pregnant, or are already pregnant, there’s an even better reason: the health of your unborn baby. Smoking during pregnancy can have a profound effect on a child’s health. And, the more you smoke, the greater the risk is.

Viral Infections Common in Babies

For many reasons, anyone who wants to have children should avoid smoking. For anyone who wants to get pregnant, quitting is hugely important. Smoking has a number of effects relating to reproduction, pregnancy, and early childhood development. For instance, smoking can reduce fertility, and increase the risk of sudden infant death syndrome. It’s also well-known that children whose mothers smoked during pregnancy have a higher risk of contracting viral infections after birth.

What does the Research Show?

Studies and reviews carried out in the last decade clearly show a link between smoking during pregnancy, and a higher risk of viral infection after a child is born. Some findings include:

  • Smoking in pregnancy is associated with a higher risk of hospitalization and mortality due to viral infection. This includes for both respiratory and non-respiratory viral infections.
  • Smoking in pregnancy reduces birth weight by up to 15 grams per cigarette smoked daily. However, this effect is strongest at low levels of exposure. This means that cutting down on smoking during pregnancy isn’t as effective as quitting altogether.
  • Both prenatal and postnatal parental smoking contributes to a higher risk of viral infections. After birth, the effect is strongest when the primary caregiver is a smoker.
  • Lung function is impaired by up to 51% in children who are born to mothers who smoked during pregnancy.
  • Children born to mothers who smoke in pregnancy have a higher risk of childhood asthma.
  • As adults, these children may have a higher risk of chronic obstructive pulmonary disorder.

Why is the Risk of Viral Infection Higher?

One of the most significant consequences of prenatal cigarette smoke exposure is that it causes a reduction in foetal breathing movements. These movements aren’t necessary to supply a growing foetus with oxygen—the placenta does that—but are vital if the lungs are to grow and mature as normal. When foetal breathing movements are impaired, for instance by cigarette smoke exposure, the result is that once a baby is born and must breath on its own, the lungs are less effective than they should be. This can continue to affect the child throughout adolescence and into adulthood.

Smoking during pregnancy also increases the foetal heart rate. This, together with the other effects of foetal smoke exposure, is what causes the higher risk of viral infection. All of these effects combine to make the new born baby more vulnerable to viral infections. With weaker lungs and a lower birth weight, they are much more susceptible to infection than other new born babies. These and other problems persist throughout childhood, and beyond.

It’s also important to understand that not only is the risk of viral infection higher, the risk of a severe, even life-threatening infection is higher too. For a developing foetus, there is no safe level of cigarette exposure.