Carbon monoxide (CO) is a colourless, odourless and tasteless poisonous gas. You can't see it or smell it. It is present in cigarette smoke(not e-cigarettes), but also in faulty gas boilers and car exhaust fumes.

It replaces some of the oxygen carried by your red blood cells, which means less oxygen getting to your baby. It is dangerous because it slows your baby’s growth and development, and increases the risk of miscarriage, stillbirth and sudden infant death.

All women are offered screening for carbon monoxide:

  • You blow into a hand-held machine, called a CO monitor, which measures the level of CO in your body.
  • The more CO you have inhaled, the higher your CO reading will be.

This test can also show whether you’re inhaling harmful amounts of second hand smoke (passive smoking). If your CO reading is above 4pm you will receive advice from your midwife on stop smoking services or advised to contact the Health and Safety Executive gas safety line.

No. Electronic cigarettes do not contain carbon monoxide or many of the other harmful gases found in cigarettes. If you are using electronic cigarettes only you will not have a higher reading in a CO test.