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Premature Labour

woman in labour
 

What is Premature Labour?

Premature labour, also sometimes referred to as preterm labour, is defined as regular contractions before 37 weeks of pregnancy, that are accompanied with changes in the cervix. Premature birth occurs in about 5-10% of all births in developed countries, and is often a result of premature labour. However, there are other things that can lead to premature birth, such as the rupture of foetal membranes, abnormalities of the uterus, and other medical problems.

Why is premature labour a problem?

Premature labour can result in premature birth. Preterm birth is the leading cause of infant death as premature babies usually have several difficulties breathing, regulating their body temperature, digesting food, and with their liver function. These problems occur in premature babies because their body systems have not had enough time to develop properly.

Breathing problems – Respiratory Distress Syndrome (RDS)

RDS is the most common cause of neonatal death. By the 7th month of pregnancy, the respiratory system is developed and mature enough to support life. However, infants born at this time do not have a substance called pulmonary surfactant in their lungs which is necessary for normal breathing. This lack of surfactant causes the airways of the lungs to collapse whenever the baby breathes out, so that it takes a lot of effort to reinflate the lungs. This requires the infant to use a large amount of energy to breathe, which can lead to respiratory distress syndrome (RDS). The difficulty in breathing can result in the brain and other essential organs not receiving adequate amounts of oxygen.

Treatment

RDS may be treated in hospital by providing the infant’s lungs with oxygen-enriched air to keep the lungs inflated between breaths, while giving surfactant to the baby at the same time.

Problems regulating body temperature

The hypothalamus, which is the part of the brain that normally controls body temperature, is not properly developed in a premature baby, so that it cannot regulate its body temperature effectively. The infant may as a result get too cold and develop hypothermia.

Treatment

The infant’s body temperature is usually regulated in hospital by placing the baby in a warmer.

Digestive problems

Infants that are more than 8 weeks premature have digestive tracts that are too poorly developed for a normal diet of breast milk.

Treatment

Infants with digestive problems are fed a low fat formula, since they cannot absorb fat very well. They are also given calcium and vitamin D supplements to promote bone formation.

Liver problems

Premature babies have poorly developed livers that produce insufficient amounts of a substance called albumin. This leads to a condition known as hypoproteinemia, where there is an abnormally low level of protein in the blood. A excess of fluid of the body tissues can develop from this, known as oedema, and may cause the tissues to swell. The liver also may not secret sufficient amounts of blood clotting factors, causing the infant to bleed easily.

Jaundice is another condition that may develop in premature infants because the liver cannot dispose of its bile components effectively. Jaundice is a yellowing of the skin and other tissues of a newborn infant. It is generally harmless and disappears on its own. It is common in many infants regardless of when they are born, but is especially more common in premature babies.

Futher details on treatment after birth can be found later in this article.

What causes premature labour?

 

The exact cause(s) of premature labour is not known. Most premature births occur as a result of spontaneous premature labour of unknown cause. This is mainly because we still do not exactly what causes normal labour in women. The changes in a woman’s hormone levels just before labour occurs remain unknown, so that it is difficult to predict when normal labour at term is going to take place, let alone premature labour.

Some scientists think that it is a change in uterine receptor function that leads to labour. It is therefore possible that this change in receptor function may play a part in the onset of premature labour.

Other causes of premature labour that are more well established are generally due to complications of the mother and/or baby. These include infections of the genital tract, such as chlamydia. Substances produced by the bacteria present at the infection may cause a woman’s water to break early. Other factors that cause the water to break may also cause premature labour.

Other major causes of premature labour include having multiple pregnancies, having too much amniotic fluid in the uterus, and foetal abnormalities. In addition, premature labour is sometimes induced for medical reasons when other complicating factors are present.

Will a premature baby survive?

Survival rates for premature infants depend on the gestational age and their birthweight. Premature infants who are born closer to term and weigh more generally have a better chance of survival.

Infants born at 22 weeks gestation or earlier have a very low survival rate (close to 0%) while those born at 24 weeks have a 54% chance of survival. At 26 weeks, this increases to 82%, and to 95% at 30 weeks in developed nations.

What are the symptoms of premature labour?

You should consult your midwife or doctor immediately if you experience any of the folloing symptoms of premature labour during the second or third trimester of your pregnancy before 37 weeks. These symptoms include an increase in the amount of vaginal discharge, vaginal bleeding/spotting, a change in the type of discharge (eg. more watery or mucous-like), abdominal pain/cramping similar to period pains, and more than four contractions in one hour even if they are painless. Feelings of pressure on the pelvis and lower back pain are also sometimes symptoms of premature labour.

Recognising the symptoms of premature labour can often be confusing as several symptoms such as sporadic early contractions or lower back pain also occur during a normal pregnancy. This makes it very difficult for women to know whether they are experiencing a symptom of premature labour, or simply going through a normal pregnancy. If you feel uncertain or worried, you should not hesitate to consult your midwife/doctor.

Who is at risk of having a premature baby?

It is important to note that some women may experience some or all of the following risk factors and still carry the pregnancy to term, and that others have none of the risk factors and still have a premature delivery. Risk factors increase the already potential chance of going into premature labour.

Medical factors

If you have had a previous premature baby, your risk of having a subsequent one is significantly increased. Women with a short cervical length (shorter than 25 millimetres) are also likely to go into premature labour. Infections of the genital tract, mutiple pregnancies, uterine/cervical abnormalities, previous surgery to the cervix, previous abortions, problems with the placenta and previous miscarriages are all also risk factors.

Some chronic maternal illnesse are also associated with premature labour. These include diabetes, sickle cell anaemia, and severe asthma. Non-uterine infections can also impact on the premature onset of labour, such as kidney infections, abdominal surgery (eg. having your appendix removed), and periodontitis (inflammation of soft tissues surrounding the teeth).

There is also a genetic component of premature labour/birth, making them more common in certain families. This may help explain the different rates seen across various sub-populations when the other risk factors are accouted for.

Social and lifestyle factors

Mothers who work physically demanding jobs for long hours have been found to be at increased risk of having premature deliveries. Women of low socio-economic status are also at risk. Young mothers (15 years or younger), underweight women, and unmarried/unsupported women are also at a higher risk. These factors are likely to increase the risk of preterm birth because of the increased stress they place on mothers. Severe stress levels may lead to the uterus contracting prematurely, which may result in premature birth. Habits such as cigarette smoking and using recreational drugs (eg. cannabis, ecstasy or cocaine) also increase the risk of premature delivery.

How is premature labour prevented and treated?

Identifying patients at risk

An ultrasound can identify women with a shorter cervical length (shorter than 25 millimetres) who are at increased risk of going into premature labour. An ultrasound is non-invasive and is usually carried out during a normal pregnancy. It uses high-frequency sound waves to create images of internal organs and blood flow on a computer screen.

Women who are already experiencing possible symptoms of preterm labour such as regular contractions are often given another test called foetal fibronectin screening. This is done by taking a vaginal swab and analysing it for a substance caled foetal fibronectin (fFN). Elevated levels of fFN give a positive result in this test. A positive result however, is not very reliable. Although it suggests that the woman is at increased risk of going into premature labour, it is not a very accurate prediction that this will happen. The fFN test is much more accurate when a negative result is produced. This indicates that the woman is highly unlikely to deliver within the next 1 to 2 weeks. A negative result therefore can put a woman at ease, as well as reduce unnecessary hospitaisation and drug treatment.

Using drugs to treat premature labour

The decision to use drugs to treat premature labour can be a difficult one to make. A doctor will take into account how far along the pregnancy is, the probability of progressive labour, and the risks of treatment to the mother and baby, before deciding to use drugs. 80% of women who appear to be having symptoms of premature labour do not actually have a premature delivery. The aim of administering any drugs is to put off delivery for as long as possible, while minimising the risk to the mother and optimising foetal conditions so that the infant has the best chance possible of surviving once it is born.

Tocolytic drugs are commonly used to treat premature labour. They are given either through in injection or taken orally. They can prolong pregnancy for 2-7 days. This time can then be used to transfer the women to a facility where she can be more closely monitored and cared for, and to administer steroids to the foetus to help the lungs to mature.

However, the use of tocolytic drugs in the treatment of preterm labour is sometimes debatable. Some studies have found that they do not prolong gestation much longer than 2 days, and do not significantly improve infant survival rates. In addition, they can have significant adverse effects on the mother including maternal death.

The most beneficial treatment of premature labour appears to be giving the foetus corticosteroids which allows the foetal lungs to mature. This greatly reduces the risk of respiratory distress symdrome (RDS).

Hospital care

Treatment after birth varies according to the types of complications present.  Premature infants are commonly placed into an incubator to maintain their body temperature. Those that have breathing difficulties are also provided with oxygen which may be supplied through small tubes placed in their nostrils, or through a ventilator pumping air into a breathing tube inserted into the airway. Fluids and nutrients may also be given via an intravenous line in the hand, foot, arm, leg or scalp. This IV line is also used to deliver drugs if needed.

Most premature infants require support with breathing and feeding until they are mature enough to do so unassisted. Some complications may also require that surgery be performed

References

 

1. ACOG Committee on Practice Bulletins – Obstetrics. Management of preterm labour. ACOG Practice Bulletin. 2003; 101(5): 1039-1044.

2.  Bernal AL. Overview. Preterm labour: mechanisms and management. BMC Pregnancy and Childbirth. 2007; 7(Suppl 1): S2.

3. Cook CM, Peek MJ. Survey of the management of preterm labour in Australia and New Zealand in 2002. The Australian and New Zealand Journal of Obstetrics and Gynaecology. 2004; 44(1): 35-38.

4. Haas DM. Preterm birth. BMJ Clinical Evidence. 2005; 14: 1-20.

5. Jones HP, Karuri S, Cronin CMG et al. Actuarial survival of a large Canadian cohort of preterm infants. BMC Pediatrics. 2005;40.

6. Murphy MJ, Fowlie PW, McGuire W. Obstetric issues in preterm birth. British Medical Journal. 2004; 329(7469): 783-786.

7. Saladin KS. Anatomy and Physiology – the unity of form and function. 3rd ed. New York. McGraw-Hill; 2004.

8. Steer P, Flint C. Preterm labour and premature rupture of membranes. British Medical Journal. 1999; 318(7190): 1059-1062.

 

Dates

Posted On: 27 January, 2008
Modified On: 13 March, 2014

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