Causes of Preterm labour
What is the meaning of "preterm"?
This might seem obvious but the truth is it is not clearly understood by everyone and that might include some of those providing obstetric care.
"Pre-term" describes the gestation period between 24 weeks and just under 37 weeks.
If symptoms appear before 24 weeks of gestation, this is a threatened miscarriage and not preterm labour. The reference cut-off point in the United States is 20 weeks. It is 24 weeks elsewhere in the world.
37 completed weeks onwards is ‘Term’ and labour at any stage thence is in order. After 42 weeks, it becomes post-term.
"Term" therefore spans a period of five weeks- from 37 to 42 weeks. It is not a fixed date.
So what is preterm labour and how can it be recognized?
Between 24 and 37 weeks, if there are uterine contractions, usually regular and painful (and occasionally painless), accompanied by changes to the cervix, then this is preterm labour.
Other symptoms include low backache which may be quite distressing, a feeling of pressure in the pelvis and occasionally the passage of a mucous blood-stained discharge, popularly called a "show".
Does preterm labour inevitably lead to delivery?
No. In fact, in about 50 per cent of expectant mother who have symptoms suggestive of preterm labour, examination reveals no cervical change whatsoever. Technically, this is not preterm labour, and almost all will resolve without any action.
However, when symptoms are there even in the absence of supporting clinical evidence, observation in hospital is the preferred form of management. In those cases where the cervix is found to be already thinning and dilating, the outlook for continuation of the pregnancy is less favourable and many - probably the majority - will go on to deliver within hours and, at most, days
What causes preterm labour?
In the vast majority of cases, the cause remains unidentified. To be realistic, one has to talk of factors that may predispose to preterm labour rather than causes of preterm labour. There are a good number of risk factors that predispose to preterm labour. These include:
Abnormalities of the womb or cervix
Multiple pregnancy - the greater the number of fetuses, the greater the likelihood of preterm labour
Excessive amounts of amniotic fluid (hydramnios)
Extremes of maternal age - the very young and the older mother (late thirties onwards) are more prone
Serious infection, not necessarily of the genital tract.
Urinary tract infection (UTI)
Fetal death. Death of the fetus is usually followed by the onset of labour within days.