Why does morning sickness happen?

Causes of morning sickness

There is a theory that suggests that morning sickness is actually an evolutionary adaptation which protects an expectant mom and her growing baby from food poisoning. Nausea and vomiting is thus the body’s way of expelling contaminated foodstuffs which would affect the survival changes of both herself and her baby. To some extent, this makes sense. A developing baby does not have sufficient protection against toxins like a grown adult has. Adult humans have a wide range of detoxification enzymes in the body which are produced in the liver.

For a growing baby, developing organs are at their most vulnerable to toxins between 6 and 18 weeks (usually about the time that morning sickness takes effect in early pregnancy). A baby is thus vulnerable to any amount of toxins present in the body, however small.

Most in the medical profession, however, associate waves of illness with the dramatic hormonal changes a woman goes through during pregnancy. Hormones certainly play a role.

• Oestrogen: Levels of oestrogen can increase up to 100 times the normal amount during pregnancy. However, a direct causal link between morning sickness and elevated oestrogen levels has yet to be determined.
• Progesterone: Levels of this hormone also increase. This has a relaxing effect on the uterus muscles (womb), which prevents early childbirth. As a side-effect, it may also relax the body’s intestines and stomach, which can lead to excess stomach acid (acid reflux or gastroesophageal reflux disease / GERD) that causes nausea.
• Human chorionic gonadotropin (hCG): Once an embryo develops in the womb, this hormone develops. More of the hormone develops as the placenta grows. Some studies suggest that this may be another reason morning sickness occurs.

Other influencing factors may include:

• Low blood sugar levels (hypoglycaemia): As placenta drains energy from an expectant mom’s body, low blood sugar can occur. A direct link has not yet been able to prove that this influences bouts of queasiness.
• Heightened sense of smell: Pregnancy does appear to trigger heightened sensitivity to various smells and odours. This can stimulate normal triggers and result in bouts of queasiness too.

Factors which may aggravate morning sickness include:

• Multiples (twins, triplets or more)
• Stress (emotional)
• Excessive fatigue
• Frequent travel