Carbon monoxide (CO) is an extremely poisonous gas. It is toxic to use (and to most other life forms) because it sticks really, really tightly to the haemoglobin molecules in our blood.
If CO is stuck to the haemoglobin, this means that the molecules can’t carry oxygen and so we would suffocate.
At lower levels of CO, you might not die but your ability to absorb oxygen would be reduced. Oxygen is important for many chemical reactions in the body. An unborn baby may therefore not grow as quickly as it should if exposed to low levels of CO.
The most likely source of CO is from cigarette smoke – which is one of the reasons why women are advised not to smoke during pregnancy. There is also the danger of exposing the baby to the cancer-causing chemicals in cigarettes.
I would imagine that CO would be very harmful to unborn babies – it latches on to hemoglobin in the blood but unlike CO2 it doesn’t let go again, meaning that it is difficult to get enough oxygen. It is a small molecule, so I would expect it to cross the placenta fairly easily. A goverment body today recommended a carbon monoxide test for expectant mothers, so that smokers (who have higher levels of CO) could get extra help to kick the habit. Smoking’s bad enough for your own health – pregnancy is a great time to quit.
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