Kensington announced on Monday Prince William and Kate Middleton are expecting baby number three.

The statement also revealed the Duchess of Cambridge is suffering from Hyperemesis Gravidarum (HG). Kate had experienced the condition with her previous two pregnancies.

Hyperemesis Gravidarum is a condition that causes severe nausea, vomiting, weight loss, and electrolyte disturbance.

"In very simple terms hyperemesis means vomiting a lot and gravidarum means in pregnancy," consultant obstetrician Daghni Rajasingam, spokeswoman for the Royal College of Obstetricians and Gynaecologists is quoted as saying by The Sun. "The diagnosis is given when women cannot keep food or fluid down because she has severe vomiting.

Dietary changes, rest, and antacids help treat mild cases. While severe cases require the women to stay hospital to be monitored. There they receive fluid and nutrition through an intravenous line (IV).

While the cause is not yet known, previous research suggests it may be a reaction to hormonal changes in the body.

Symptoms:

* Nausea
* Low blood pressure
* Fast heart rate
* Migraine
* Feeling lethargic

HG symptoms often occur between 4-6 weeks of pregnancy and sometimes peak between 9-13 weeks. These symptoms can worsen due to fatigue, prenatal vitamins, diet, hunger and odours.

Information Source: American Pregnancy Association