Causes Of Preterm Birth

Read about various factors that can contribute to premature labour, such as smoking and infections. Steps can be taken to avoid premature labour.

Key points

  • Some premature births can be caused by problems with the fetus, the mother or both.
  • Certain events can stimulate the onset of premature labour including placental abruption, incompetent cervix, hormonal changes or infection.
  • There are multiple risk factors for premature birth including having a previous premature birth, pregnancy with multiple babies, infection, drug or alcohol use, and age.
  • While some risk factors cannot be changed, there are a few general ways to reduce the odds of having a premature birth.
Preterm birth, or premature birth, is usually an unplanned event. Depending on the causes of the birth and how premature the baby is, it may also be an emergency. This section explores the causes of premature birth, the signs of premature birth, and strategies to delay premature birth. In many cases, premature birth cannot be avoided.

Premature birth can have many causes which include problems with the fetus, the mother, or both. However, about fifty percent of the time, the cause or causes of a premature birth are unknown.

When the cause is known, premature birth most frequently comes as a result of a premature rupture of the fetal membranes which initiates labour.

Certain events can stimulate the onset of premature labour. These include:
  • Placental abruption, where the placenta separates from the uterus during pregnancy
  • Incompetent cervix, where the cervix painlessly and gradually opens before the time it is supposed to
  • Hormonal changes, which can cause stress in the unborn baby or mother
  • Infection

Risk factors for premature labour

There are a number of factors that can put a pregnant woman at higher risk for having a premature labour and delivery. If you had a previous premature labour, your chance of having another premature labour increases two and a half times. That rate jumps to 10 times if your previous premature labour occurred before the 28th week of pregnancy. It is important for you and your health care provider to keep this in mind, so that they can provide you with appropriate care throughout your pregnancy.

Another major risk factor for premature labour and delivery is being pregnant with twins or multiple babies. The rate of twins and multiple babies has increased over the past few years, mostly because of the use of fertility drugs and other assisted reproduction techniques. About half of all twins deliver at 36 weeks or less. Half of triplets deliver before 32 weeks. Many mothers of twins and multiple babies go into premature labour spontaneously. Others may need to have premature labour induced because of complications during pregnancy.

One important risk factor is infection. Some types of infection that can result in premature birth are as follows:
  • Untreated urinary infections: These double the risk for premature birth. Urinary infections are screened at each medical visit, and can be treated with antibiotics.
  • Bacterial vaginosis: These also double the risk for premature birth. The main symptom of vaginosis is a light or heavy vaginal discharge with a slight “fishy” smell. Vaginosis is treated with antibiotics.
There are a number of other risk factors for premature labour and delivery. Some of these risks, such as anemia, slow maternal weight gain, stressful work habits, smoking, drinking alcohol, and using drugs like cocaine, can be rectified during pregnancy.

Other risk factors for premature birth include age under 17 years or over 40 years, prior multiple abortions, and low pre-pregnancy weight.

Knowing these risks can help you and your health care provider determine whether you will need special care to prevent premature labour. If you are at high risk of going into premature labour, your health care provider can take special precautions to ensure the best outcomes for you and your baby.