The nausea and vomiting of pregnancy (NVP) - ‘morning sickness’ - is common in early pregnancy. Thought to affect 70-85 per cent of pregnant women (Cochrane Database Syst Rev, 2003; 4: CD000145), and often accompanied by tiredness and lethargy, these symptoms usually clear after the first three months, but can, in some cases, last throughout the pregnancy.

The following factors have been suggested as playing contributory roles: low blood pressure and blood sugar levels; hormonal changes; emotional ambivalence towards pregnancy; and vitamin and mineral deficiencies (especially iron and vitamin B6). Eating too much refined, greasy or spicy foods is also blamed. Also, pressure on the stomach from the growing uterus can interfere with proper digestion, and this may be another cause of the condition.

Despite the sheer volume of women who suffer from the condition, morning sickness is not well understood and often poorly treated (J Perinat Neonatal Nurs, 2004; 18: 312-28).

A number of drugs can also cause nausea and vomiting as side-effects, including antibiotics, NSAIDs, thiazides, oestrogens and - ironically - iron. If you’re on any other drugs, check out their side-effects.

Some health practitioners believe morning sickness is more common in women carrying twins or triplets, but there is no conclusive evidence to say that this is so.

What doctors tell you
Although there is no currently approved medication for morning sickness, doctors may suggest taking antacids, sugar solutions or antihistamines, all of which can be purchased over the counter.

There are also drugs used to manage nausea and vomiting by acting either directly on the digestive tract or on the brain. Drugs that act on the digestive tract increase intestinal contractions and accelerate food transit. Centrally acting agents act on the vomiting centre (chemoreceptor trigger zone; CTZ) in the brainstem to block the nerve impulses that trigger nausea and vomiting. These include dopamine antagonists, anticholinergics and antiserotonin agents (ondansetron).

Severe vomiting is dangerous for both mother and baby, as vital minerals and nutrients can be lost through dehydration. Symptoms include dizziness, thirst, passing less urine than usual (or none at all) or passing dark urine. A midwife or GP can take a simple urine (ketone) test to confirm the degree of dehydration. In extreme cases, the patient may need to go to hospital, where fluids can be given through an intravenous drip.

Isabel Atherton