‘Normal’ morning sickness:

It seems a while ago now but very early in Kate Middleton’s pregnancy she was hospitalised with severe morning sickness – a quite rare condition known as hyperemesis gravidarum.

But what is ‘normal’ morning sickness and why do so many women experience it in early pregnancy?

According to obstetrician, Dr Roger Harms, morning sickness in the form of nausea and vomiting in the first trimester can be a sign of a healthy pregnancy.

“A study of more than 2,400 pregnant women associated nausea and vomiting during the first trimester with a reduced risk of early pregnancy loss — particularly for women age 30 and older.”

Dr Harms says that shortly after a fertilised egg attaches to your uterine lining, your body begins to produce a hormone called human chorionic gonadotropin (HCG).

“While the cause of nausea during pregnancy isn't clear, nausea typically begins when production of HCG begins. As a result, nausea during pregnancy might indicate that you're experiencing the normal climb in pregnancy hormones needed for a healthy pregnancy,” says Dr Harms.

Other theories suggest that nausea during pregnancy might:

• reduce foetal exposure to potentially dangerous substances in your diet
• encourage you to eat foods that contain certain nutrients, such as those rich in carbohydrates, and
• prompt you to adjust your activity level to favour maternal and foetal tissue growth.

Dr Harms says a lack of nausea during pregnancy isn't necessarily a cause for concern.

“Some women fortunately don't seem to experience common symptoms of early pregnancy despite the generous production of pregnancy hormones.”

But severe morning sickness can signal a problem. Severe nausea and vomiting can indicate a molar pregnancy — when the placenta develops into an abnormal mass of cysts rather than becoming a viable pregnancy — or the same condition as the Duchess of Cambridge that can cause loss of weight and body fluids and might require treatment with intravenous fluids and medications.

Dr Harms says any woman who is concerned about morning sickness or wonders whether her morning sickness is normal, should consult their family doctor.