What Is Preterm Birth? – Signs, Causes & Treatment

By (gynecologist), (embryologist) and (fertility counselor).
Last Update: 11/27/2014

Premature delivery or preterm delivery is the one that takes place before the 37th week of pregnancy. It presents gynaecological complications and complications for the newborn baby, since it may lead to many health problems in the child, or even to his death. It’s calculated that approximately 5% to 10% of the deliveries are premature.

It must be taken into account the fact that pregnancy usually lasts 40 weeks and they begin to count from the woman’s last period.

Provided below is an index with the 6 points we are going to expand on in this article.


Even though in some cases the suspicion of a premature deliver may arise, the cause of the premature delivery is not known yet. There are several factors that must occur in order for delivery to take place, but four main causes have been identified over the years: uterine overdistension, uterine infection or inflammation, decidual bleeding and precocious fetal endocrine activation.

Although a woman may have a normal pregnancy and take all the necessary precautions, it’s possible that preterm delivery takes place. There are several studies that show that black women have more possibilities to suffer from premature delivery than white women, however the cause of the differences between races is still unknown, even though research is being carried out.

Even though the cause is usually unknown, there are several factors that play a role on premature delivery.

Risk factors

In order to analyse the risk factors, they tend to be divided depending on their nature.

On the one hand, we can talk about the habits of the mother during pregnancy: unhealthy behaviours while pregnant, such as the consumption of alcohol and drugs or smoking are risk factors. If the pregnant woman suffers from obesity or has put on a lot of weight during pregnancy, the likelihood of preterm delivery increases.

Some conditions during gestation may increase the probability of premature delivery, for instance:

  • Multiple pregnancy
  • Polyhydramnios: excessive amount of amniotic fluid.
  • Infection in the mother, which not necessarily is a uterine infection, any kind of infection may lead to preterm delivery.
  • High blood pressure in the woman.
  • Pre-labour rupture of membranes.

Uterine alterations, such as a short cervix, uterine malformations, or a bad functioning of the placenta, such as placenta praevia or placental abruption, can cause preterm delivery.


When there are evident signs of preterm delivery, what must be done is delaying labour as much as possible and preparing for the baby’s birth, which is usually done simultaneously.

If it’s achievable, birth tends to be delayed as much as possible, so that the foetus can carry on developing and growing. In these situations, absolute rest is advised for women. Lying in bed decreases the pressure on the cervix and avoiding the weight of pregnancy, the likelihood of contractions is reduced. In the case that the woman is in hospital, intravenous serum is applied, so that the woman is as hydrated as possible and medication against the apparition of contractions may be provided.

Despite these strategies, many preterm deliveries are unavoidable. One of the most common complications in preterm babies is the fact that their lungs are not still mature and don’t produce the lung surfactant substance, provoking severe respiratory complications. Glucocorticosteroids are supplied to pregnant women to stimulate the maturation and growth of foetal lungs, but in order for them to be provided, pregnancy must have reached week 24.

Depending on the moment when the premature delivery has taken place, the newborn baby will suffer from more or less complications. Before week 28 it’s considered as extremely premature labour, between week 28 and 31 they are considered severely premature infants, and moderately premature is between week 32 and 33. The best prognosis is for those babies born between weeks 34 and 36, considered slightly premature.

FAQs from users

Is a preterm birth more likely with twins?

By Manuel Aparicio Caballero M.D., M.Sc. (gynecologist).

According to the World Health Organization (WHO), a preterm birth occurs when the child is born before the week 37 of pregnancy. Some of the most common causes of preterm birth are:

  • Overdistention of the uterus: loss of tone in the uterine musculature that prevents this organ to recover its normal size.
  • Infection or uterine inflammation: certain bacteria can damage fetal membranes by causing its rupture and triggering a preterm birth. An infection that affects the uterus directly may lead to preterm birth as well.
  • Decidual bleeding: a type of vaginal bleeding that may occur while a woman is pregnant.

There exist many risk factors that can lead to premature birth, including obesity, high blood pressure, etc. A multiple pregnancy is one of these factors.

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Authors and contributors

 Manuel Aparicio Caballero
Manuel Aparicio Caballero
M.D., M.Sc.
Bachelor's Degree in Medicine from the University of Murcia. Specialist in Obstetrics & Gynecology. Master's Degree in Human Reproduction from the King Juan Carlos University and the IVI. Currently, he is part of the team of Tahe Fertilidad (Murcia, Spain). More information about Manuel Aparicio Caballero
License: 303008030
 Neus Ferrando Gilabert
Neus Ferrando Gilabert
B.Sc., M.Sc.
Bachelor's Degree in Biology from the University of Valencia (UV). Postgraduate Course in Biotechnology of Human Assisted Reproduction from the Miguel Hernández University of Elche (UMH). Experience managing Embryology and Andrology Labs at Centro Médico Manzanera (Logroño, Spain). More information about Neus Ferrando Gilabert
Adapted into english by:
 Sandra Fernández
Sandra Fernández
B.A., M.A.
Fertility Counselor
Bachelor of Arts in Translation and Interpreting (English, Spanish, Catalan, German) from the University of Valencia (UV) and Heriot-Watt University, Riccarton Campus (Edinburgh, UK). Postgraduate Course in Legal Translation from the University of Valencia. Specialist in Medical Translation, with several years of experience in the field of Assisted Reproduction. More information about Sandra Fernández

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