Preterm birth is a major cause of neonatal death and can lead to long-term health problems such as learning disabilities, vision and hearing impairment, chronic lung disease and cerebral palsy.

In addition to the personal trauma and difficulties that preterm birth can bring to a family, it can also lead to significantly increased healthcare costs and long-term demands on many broader aspects of society (Fernandez Turienzo et al. 2016).

Even though the dangers of preterm birth are widely acknowledged, preventing premature labour is a problem that doesn’t yet have an effective solution and there are very few risk reduction strategies that are truly effective.

How Common is Preterm Birth?

Preterm birth is defined as birth before 37 completed weeks of pregnancy. With more than 1 in 10 babies born prematurely every year, policies that effectively reduce preterm birth, along with the associated economic, social and personal costs, are becoming more important than ever (Morris, Brown & Newnham 2020).

In Australia, it’s currently estimated that 1 in 12 pregnancies ends prematurely, resulting in more than 36 000 preterm births every year (Australian Preterm Birth Prevention Alliance 2021).

Data from the Australian Department of Health (2019) found that in 2014:

• 8.6% of babies were born preterm, with most births occurring between 32 and 36 weeks gestation
• The average gestational age for all preterm births was 33.3 weeks
• Babies whose mothers smoked during pregnancy were more likely to be born preterm.

The following sub-categories of prematurity are based on the gestational age of the fetus, with all stages of prematurity associated with adverse outcomes and both short and long-term consequences, particularly in terms of neurodevelopment (White & Newnham 2019):

• Extremely preterm (< 28 weeks)
• Very preterm (28 to < 32 weeks)
• Early preterm (< 34 weeks).

Predisposing Factors

Even though there have been many advances in maternity care in recent years, the rate of preterm births continues to rise, leading researchers to look more closely at a wide range of risk factors and potential interventions. These interventions range from those supported by high-quality evidence-based research to customs and traditions that have little proven value (Fernandez Turienzo, Sandall & Peacock 2016).

Significant risk factors include:

• Previous preterm birth or mid-trimester loss (at 16 to 34 weeks gestation)
• Previous preterm rupture of membranes < 34 weeks
• Previous cervical cerclage v
• Known uterine variant (unicornuate uterus, significant bicornuate uterus or uterine septum)
• Ashermann’s syndrome (intrauterine adhesions, or scarring)
• Social disadvantage and low levels of maternal education
• Diabetes or gestational diabetes
• Current urogenital infections such as chlamydia and bacterial vaginosis
• Excessive smoking and alcohol consumption.

(Royal Cornwall Hospitals NHS Trust 2020; DoH 2019)

Intermediate risk factors include:

• A previous caesarean section at full dilatation
• History of single large loop excision of the transformation zone (LLETZ) procedure to remove part of the cervix with a depth > 10mm
• More than one LLETZ procedure (irrespective of depth)
• Cone biopsy (by knife or laser, irrespective of depth).

(Royal Cornwall Hospitals NHS Trust 2020)

Other recognised risk factors include:

• Young (< 20 years) or older (≥ 40 years) pregnancy
• Short inter-pregnancy intervals
• Nutritional deficiencies
• Underlying medical conditions
• Multiple pregnancy
• Living in a remote area.

(DoH 2019)

With such a wide variety of potential risk factors, premature birth can be difficult to prevent, and further research is needed into special antenatal care packages for women who present with significant risk factors (Fernandez Turienzo, Sandall & Peacock 2016).

Reducing the Risk of Preterm Birth

Although preterm birth cannot be entirely prevented, many of the risk factors can be reduced with appropriate care, and all women should be screened for potential risks.

For example, it’s well known that smoking can increase the risk of preterm delivery, so appropriate advice and support should be given from the earliest opportunity during antenatal visits. Along with smoking cessation advice, screening for lower genital tract infections, zinc supplementation and the introduction of midwifery-led continuity of care are all interventions that are known to help reduce the incidence of premature labour.

Interestingly, the use of a cervical stitch (cerclage), which used to be considered beneficial for women with a shortened cervix, is only of help for women who are at high risk of preterm birth and who have a singleton pregnancy. Other interventions such as bed rest and home uterine monitoring, although often recommended, don’t appear to offer any significant benefits (Medley et al. 2018).

A recent Cochrane review also found no evidence to either support, or refute, bed rest as a preventative measure, but did find that in women at high risk of preterm birth, activity restriction was associated with an increased risk of the early onset of labour.

Modifying the Risks

In cases where significant risks of preterm labour are identified, all possible steps should be taken to address modifiable risk factors. For example:

• Having adequate social and emotional support
• Quitting smoking and avoiding exposure to passive smoke
• Avoiding alcohol whilst pregnant
• Having tests to exclude urogenital infections
• Taking regular exercise and maintaining a healthy weight.

As Wisanskoonwong, Fahy and Hastie (2011) suggest, many medical interventions aimed at preventing, and not just delaying, preterm birth don’t seem to be effective. Yet, providing holistic antenatal midwifery care for women living in disadvantaged socio-economic circumstances, or who have an increased risk of preterm birth, does seem to have a positive influence, and can help reduce the rate of prematurity.

Significant progress is still clearly needed in order to gain a better understanding of the multicausal and complex nature of premature birth. Without this understanding, creating effective research protocols becomes much harder.

However, one area that does seem to be showing positive results is the relationship between the mother and her midwife, as this is thought to have a significant role to play in preventing preterm labour. As Fernandez Turienzo, Sandall and Peacock (2016) suggest, further research is needed to clarify whether a midwifery-led continuity model of antenatal care and a closer relationship between mother and midwife can significantly influence the incidence of premature birth.

Alongside this, more comprehensive research is needed to explore the effectiveness of risk-screening tools to predict preterm labour. Although there are no preventative strategies that can effectively prevent preterm birth, there are suggestions that future studies should consider treating gestational age as a continuum rather than as a set cut-off date between term and preterm. As Fernandez et al. (2016) suggest, this could offer a better reflection of the biological processes of birth, which do not change suddenly at 37 weeks.

Fernandez et al. (2016) also point out that the analysis of gestational age as a continuous variable could potentially provide statistical data with much greater relevance and ultimately might allow for more innovative approaches to preventing preterm birth.

References

• Australian Preterm Birth Prevention 2021, How To Prevent Preterm Birth, Australian Preterm Birth Prevention, viewed 6 August 2021, https://www.pretermalliance.com.au/Mothers-to-be/How-To-Prevent-Preterm-Birth
• Department of Health 2019, Pregnancy Care Guidelines: 23 Risk of Preterm Birth, Australian Government, viewed 6 August 2021, https://www.health.gov.au/resources/pregnancy-care-guidelines/part-d-clinical-assessments/risk-of-preterm-birth
• Fernandez Turienzo, C, Sandall, J & Peacock, J 2016, ‘Models of Antenatal Care to Reduce and Prevent Preterm Birth: A Systematic Review and Meta-Analysis’, BMJ Open, vol. 6, no. 1, viewed 6 August 2021, https://bmjopen.bmj.com/content/6/1/e009044
• Medley, N, Vogel, J, Care, A & Alfirevic, Z 2018, ‘Ways to Help Pregnant Women Avoid Preterm Birth’, Cochrane, viewed 6 August 2021, https://www.cochrane.org/CD012505/PREG_ways-help-pregnant-women-avoid-preterm-birth
• Morris, J, Brown, K & Newnham, J 2020, ‘The Australian Preterm Birth Prevention Alliance’, Australian and New Zealand Journal of Obstetrics and Gynaecology, vol. 60, no. 3, viewed 6 August 2021, https://obgyn.onlinelibrary.wiley.com/doi/10.1111/ajo.13171
• Royal Cornwall Hospitals NHS Trust 2020, Preterm Birth, Preterm Labour and Delivery Prevention Clinical Guideline V2.2, NHS, viewed 6 August 2021, https://doclibrary-rcht.cornwall.nhs.uk/DocumentsLibrary/RoyalCornwallHospitalsTrust/Clinical/MidwiferyAndObstetrics/PretermBirthPretermLabourAndDeliveryClinicalGuideline.pdf
• White, S & Newnham, J 2019, ‘Is it Possible to Safely Prevent Late Preterm and Early Term Births?’, Seminars in Fetal and Neonatal Medicine, vol. 24, no. 1, pp.33-36, viewed 6 August 2021, https://www.sfnmjournal.com/article/S1744-165X(18)30125-2/fulltext
• Wisanskoonwong, P, Fahy, K & Hastie, C 2011, ‘The Effectiveness of Medical Interventions Aimed at Preventing Preterm Birth: A Literature Review’, Women and Birth, vol. 24, no. 4, pp.141-147, viewed 6 August 2021, https://pubmed.ncbi.nlm.nih.gov/21277271/