A premature birth, or preterm delivery, is the birth of a baby before 37 completed weeks of pregnancy. Babies are considered to be full term from 37 weeks of pregnancy and will have a maximum chance of healthy development, and allow their bodies enough time to develop and function well if they are born from this time.
Recent UK wide data indicates that around one in eight babies requires some form of special care. This equates to over 80,000 babies. Despite improvements in antenatal and neonatal care, the number of premature babies born each year has not significantly decreased since the 1960s. It remains very difficult to identify women and babies at risk because the causes of premature labour are not yet fully understood.
What causes premature birth?
More work is needed to understand the causes of premature labour. Research has identified some risk factors that may increase a woman's chance of having a premature baby, although it is important to acknowledge that many women with no known risk factors will have a preterm labour. In fact, the majority of premature births occur without any obvious cause or known risk factors.
Some known risks are listed below.
Multiple pregnancy - the overstretching of the womb that occurs in the case of twin or triple pregnancies is thought to increase the risk of premature labour.
Maternal age- this is not a major factor, but it is recognised that mothers under 20 or over 35 years of age have a slightly higher risk of preterm labour.
Fetal development - 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.
Lifestyle factors - some habits or lifestyle influences of the mother can increase the risk of having a premature baby. These include smoking, using recreational drugs, having a high caffeine intake, having a poor diet or being underweight, and engaging in overstrenuous 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 - there are certain medical conditions specific to pregnancy, which if left untreated or become severe during pregnancy can cause preterm labour. Examples include pregnancy-induced diabetes and Pre-Eclampsia, (which in itself is a cause of at least 15% of all pre-term births), and Obstetric Cholestasis (liver disease characterised by excessive itching).
Maternal medical conditions - there are certain medical conditions which a woman might already have prior to becoming pregnant, which have been linked to an increased risk of premature birth. For example, if a woman is diagnosed with the conditions, Systemic Lupus Erythematosus (SLE), Antiphospholipid Syndrome (APS), or renal disease, she may be at increased risk of premature labour.
Infection - 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.
Cervical incompetence - this term refers to the cervix, the opening of the womb. In some women, the cervix will shorten and open too soon and labour will spontaneously follow.
Other - there are other possible links and risks discovered by researchers and often published. Some are more significant than others, and some research is only relevant to certain groups of people, but all research is welcome. For example, one study found women with chronic gum disease in the second trimester of pregnancy were seven times more likely to have a preterm labour. It is also important to note that whilst many of these conditions are risk factors for premature birth and may cause spontaneous labour (contractions starting or waters breaking on their own), there are also circumstances where premature delivery is initiated by the medical staff.
For example if a woman suffers from pre-eclampsia or the baby is not thriving in the womb, or if there is an antepartum bleed and either the health of the mother or the baby is at risk, then premature delivery of the baby may be the only option.
What are the implications of premature birth for the mother and the baby?
Whilst the experience of a premature birth may be very traumatic for all the family involved, there is seldom any adverse effect upon the mother's physical health. Once preterm labour is suspected most women will receive drugs to attempt to stop contractions (tocolytic drugs). These may stop labour altogether or may delay the onset of labour for enough time for steroids to be administered to the mother, which help the baby's immature lungs develop before delivery and if necessary to try to delay birth until the mother is transferred to a hospital with an available Special Care Baby Unit (scbu) cot.
For the mother, physical recovery from premature labour and delivery will be no different than from a later delivery although there can be greater emotional stress.
The survival rates and levels of long-term disability for premature babies are related to the gestational age of the baby. Babies born closer to their due date and with a good birth weight will have a greater chance of survival than very small, very premature babies. Premature babies have less time in the womb to mature and develop, as a result they're often at increased risk of medical and developmental problems. However, neonatal care is making huge advances, and there are many wonderful stories of tiny babies surviving despite the odds against them.