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Small preterm baby in an incubator with many tubes attached and wearing a knitted yellow hat

Risk factors and preventative practices for premature birth

Preterm birth is defined as birth occurring before 37 completed weeks of gestation. It is broadly divided into two categories, spontaneous or health provider-initiated, but there can be some overlap between the two when there is a risk to the mother or foetus.

  • Spontaneous preterm birth can be triggered by multiple factors but the cause, or causes, is unknown in half of all cases. Ascending infection from the birth canal is believed to be an important causative factor (Gravett et al. 2010), (Goldenberg et al. 2008).

  • Health provider-initiated preterm birth occurs when there are clinical reasons for bringing the pregnancy to an end. This happens when continuing with the pregnancy might pose a medical risk to the health of the mother or foetus. Clinical examples include severe pre-eclampsia and foetal growth restriction.

Differentiating the causes of preterm birth is important. Provider initiated preterm birth rates reflect policies and decisions within a setting in relation to the balance of risks for child and mother in continuing the pregnancy. A contributing factor across many settings with high rates of caesarean section might be aggressive management policies for poor foetal growth (Blencowe et al. 2013), (Boerma et al. 2018), (Delnord and Zeitlin 2019).

Risk factors for preterm birth

There are a number of risk factors for preterm birth:

  • Previous history: The risk of a preterm birth increases if an earlier pregnancy resulted in preterm birth. This may be due to interaction of genetic, environmental and epigenetic factors.

  • Age: A young (adolescent) or older mother increases the risk of preterm birth as does a short interval between pregnancies. Providing family planning guidance to women between pregnancies is important.

  • Lifestyle factors such as smoking, excess alcohol consumption, recreational drug use, excess physical work or activity.

  • Multiple pregnancies (twins, triplets or higher order): Twin births account for around a quarter of preterm births and multiple births increase the risk by a factor of eight. Twin, and some triplet, pregnancies occur spontaneously but higher order pregnancies are often the result of treatment for infertility such as in vitro fertilisation.

  • Infections such as urinary tract infection, malaria, HIV, syphilis and bacterial vaginosis.

  • Chronic conditions such as diabetes, hypertension, anaemia, asthma and thyroid disease

  • Nutritional status: Undernutrition, with or without micronutrient deficiencies, and obesity.

Some conditions might require health provider-initiated preterm birth:

  • Maternal health and pregnancy complications: For example, cervical incompetence, pre-eclampsia, complications such as uterine rupture.

  • Maternal psychological health: For example, depression or violence against the woman.

  • Foetal health: For example, growth restriction.

Summary list of the main risk factors for preterm birth, as described above (Click to enlarge)

Preventing preterm birth

Maternity and neonatal teams play an important role in preventing preterm birth and reducing the risk of some of its complications by taking actions before conception, during pregnancy and immediately after preterm delivery (Kindinger & David 2019).

Before conception

Health education plays an important role in reducing the risk of preterm birth by:

  • Promoting a healthier lifestyle - supporting good nutrition, encouraging weight loss in obese women, and promoting smoking and alcohol cessation.

  • Providing advice on contraception to prevent adolescent pregnancies, improve pregnancy spacing, and

  • Preventing infections such as sexually transmitted infections (STIs).

Reproductive medicine specialists can play a role in preventing preterm birth by practicing single embryo transfer and reducing the incidence of multiple conceptions through artificial reproductive techniques (McLernon et al. 2010).

Illustration of a health education class plus a summary list of ways to prevent preterm birth before conception, as described above (Click to enlarge)

During pregnancy

Regular antenatal care is important to monitor maternal and foetal well-being, detect and treat infections, and ensure optimal management of women with underlying health conditions such as diabetes and hypertension.

In women with pre-existing cervical incompetence, providing vaginal progesterone and carrying out procedures to tighten the cervix have a role but only in women with multiple previous preterm births or those who develop a short cervix late in pregnancy (Gilbert et al. 2019).

The World Health Organization strongly recommends a course of antenatal corticosteroids for women at risk of preterm birth from 24 to 34 weeks of pregnancy if gestational age can be accurately assessed, preterm birth is imminent, there is no clinical evidence of maternal infection and suitable obstetric and newborn care is available (WHO 2015). Antenatal steroids mature the lungs of the foetus, which reduces mortality, respiratory distress and ROP.

Addressing the social influences and health systems factors which lead to high caesarean section rates in some settings is recognised to be more challenging (Betrán et al. 2018).

Illustration of a doctor counselling a couple about to have a baby plus a summary list of ways to prevent preterm birth during pregnancy, as described above (Click to enlarge)

Immediately after preterm delivery

In all settings it is important that health professionals understand the importance of the first hour of life of infants born preterm. Optimal interventions during this first ‘golden hour’ can have a major impact on the baby’s subsequent clinical course. It is important to invest and plan for interventions to manage the golden hour after preterm birth. These interventions (which we will discuss this week) include:

  • Clamping of the umbilical cord later than is usual practice (Fogarty et al. 2018).

  • Keeping the baby warm (McCall et al. 2018), and

  • Avoiding giving 100% inspired oxygen and manoeuvres that over-distend the lungs (Perlman et al. 2015).

Summary list of ways to prevent preterm birth at delivery (Click to enlarge)

In your setting, what can you do to support the key actions to prevent preterm birth highlighted in this article? What are your main priorities for action? Share your thoughts in the Comments.

To guide your thinking, you can download the key messages from this article as an infographic, ‘Preventing premature birth’ (PDF).

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This article is from the free online course:

Retinopathy of Prematurity: Practical Approaches to Prevent Blindness

London School of Hygiene & Tropical Medicine