Babies born before 37 weeks gestation are considered premature, and according to Tommy's the baby charity, around 7% of all babies born in the UK in the years 2001/2002 were born prematurely.
Some babies born early are fine; they are just small. But often when a baby is born preterm, his organ systems may not have had time to fully develop.
According to Tommy's, the majority of preterm births occur without any obvious cause or known risk factors. However, there are some known risks for premature births:
The overstretching of the womb that occurs in the case of twin or triple pregnancies is thought to increase the risk of premature labour.
Not a major factor, but it is recognised that mothers under 20 or over 35 years old have a slightly higher risk of preterm labour.
If the baby is not thriving in the womb, for example, if the placental blood supply is impaired or there is evidence of growth retardation, then this can lead to premature birth.
The mother's lifestyle can increase the risk of having a premature baby. For example, smoking, using recreational drugs, having a high caffeine intake, having a poor diet or being underweight, and engaging in over-strenuous physical activity.
Previous gynaecological history:
Women who have had surgery on their cervix may have suffered damage to the opening of the womb. This can cause the cervix to open too soon in pregnancy, resulting in premature labour.
Pregnancy-specific maternal disease:
Examples of this include pregnancy-induced diabetes and pre-eclampsia (itself a cause of at least 15% of all pre-term births) and obstetric cholestasis (liver disease characterised by extreme itching).
Maternal medical conditions:
Certain pre-existing medical conditions in the mother have been linked to an increased risk of premature labour. They include systemic lupus erythematosus (SLE), antiphospholipid syndrome (APS), or renal disease.
This is another potential trigger of preterm labour. Vaginal infections, such as gonorrhoea, chlamydia, trichomonas, bacterial vaginosis and group B streptococci have all been linked to preterm labour. Bladder infections can also trigger early labour if left untreated.
In some women the cervix, the opening to the womb, will shorten and open too soon and labour will spontaneously follow.
There are also circumstances where premature delivery is initiated by medical staff. For example, if the mother is suffering from pre-eclampsia or the baby is not thriving in the womb, if there is a bleed and either the health of the mother or baby is at risk, then premature delivery of the baby may be the recommended option.