Thousands of Irish women develop the severe form of nausea and vomiting that is affecting Kate Middleton.
The condition, known as hyperemesis gravidarum, is uncommon and can lead to symptoms such as:
* Prolonged and severe nausea and vomiting.
* Ketosis – a serious condition that is caused by a raised number of ketones in the blood; ketones are toxic acidic chemicals.
* Weight loss.
* Low blood pressure when standing up.
Specialist medical care, including hospitalisation, is needed if the woman is losing too much fluid.
Although it is unlikely to affect the baby, it can cause weight loss and this increases the risk of a low birth weight.
Unlike most morning sickness, it usually persists past the first 12 weeks of pregnancy.