Premature labour Dr Trisha Macnair Around seven per cent of babies in the UK are born prematurely (before 37 weeks of pregnancy). There's often little risk for the mother, but the implications for the baby can be enormous.

In this article

Who's affected? How's it diagnosed?

What's the treatment? What are the complications?

Can it be prevented?

Any pregnant women can go into premature labour, but those especially at risk are young, single or unsupported mothers, and those who smoke or are underweight.

What causes it?

In around 40 per cent of cases, the cause of premature labour is unknown. Other causes include:

• Pre-eclampsia
• Multiple pregnancy
• Antenatal haemorrhage
• Illness in the mother, such as diabetes, high blood pressure or heart disease
• Cervical incompetence
• Foetal abnormalities or death

There's growing evidence that stress, particularly when it's sudden or severe, can induce labour.

Infection is another potential trigger. Vaginal infections such as gonorrhoea, chlamydia, trichomonas and group B streptococci have all been linked to premature labour.

Bacterial vaginosis, which changes the acidity of the vagina, is also associated with premature labour, possibly because it reduces the body's natural defences against infection.

It may be possible to reduce the risk by screening for and treating such infections with antibiotics. This must be done before labour starts.

The challenge with premature labour is to spot it before it gets going. The only absolute proof of labour is dilation of the cervix, but by then it's too late to stop the baby being born.

Contractions of the uterus can be a confusing sign. Many women experience Braxton Hicks, or 'practice', contractions from week 24 of pregnancy. Two-thirds of women diagnosed as being in labour won't have delivered within 48 hours and one in three will continue their pregnancy to full term (40 weeks).

If a woman's membranes rupture and she loses amniotic fluid, labour becomes more likely, especially as there's a risk of infection. However, urine may be mistaken for amniotic fluid and even special testing sticks can give incorrect answers.

Research has suggested that some chemicals can give a clue that labour is about to start. One example is foetal fibronectin, found in the secretions in the vagina. However, currently, such tests can only give a rough guide.

Many things have been tried to halt premature labour, including drugs to stop contractions, ties to keep the cervix from dilating and antibiotics to treat infection. However, none is very effective.

Drugs that stop contractions (tocolytics) help in about a quarter of cases, but rarely work for more than 48 hours. They also carry some risks, especially if the membranes have ruptured. Such drugs are mostly used to postpone delivery until the woman can get to a hospital with a special care baby unit.

At the same time, treatments can be given to prepare the baby for an early arrival, such as drugs to help mature the lungs. These may reduce the risk of complications, halving the severity of respiratory distress syndrome.

Babies born after 34 weeks only have a low risk of problems because their systems have almost completely matured and labour is usually allowed to continue. But those under 28 weeks need to be delivered in a hospital with a neonatal intensive care unit.

In recent years, doctors have been able to improve dramatically the survival hopes for babies born as early as 22 or 23 weeks. However, these babies face a huge battle at the start of life, with a risk of many significant long-term problems.

Premature babies are at risk of:

• Respiratory distress syndrome
• Hypothermia
• Low blood glucose
• Jaundice
• Infection
• Retinopathy of prematurity
• Necritising enterocolitis
• Death

There's often little you can do to prevent premature labour, but to reduce your risk you should:

• Stop smoking
• Get vaginal infections or discharge treated
• Report symptoms such as swollen ankles, blood loss or fluid loss
• Keep fit and healthy
• Avoid excessive stress

This article was last medically reviewed by Dr Rob Hicks in July 2006.