Prediction and prevention of spontaneous preterm birth in the general population

#Background

This section of Taonga Tuku Iho provides recommendations of practice on the identification and modification of risk for spontaneous preterm birth, including second trimester miscarriage, occurring after PPROM and/or preterm labour. It is relevant to pregnancy care for all wāhine/people.

For those identified to have a high chance of spontaneous preterm birth, including second trimester miscarriage, due to factors that may be modified through specialised preterm birth pregnancy care, additional recommendations and practice for pregnancy care are provided in Prediction and prevention of spontaneous preterm birth in specialised preterm prevention care.

For wāhine/people with signs or symptoms of preterm labour (threatened preterm labour) and/or preterm prelabour rupture of membranes (PPROM), recommendations and practice on the prediction and prevention of spontaneous preterm birth in these clinical scenarios are provided in Preterm prelabour rupture of membranes (PPROM) and threatened and active preterm labour.

Spontaneous preterm birth may occur following the spontaneous onset of labour and/or PPROM <37⁺⁰ weeks gestation. The lower limit of preterm birth may be considered as birth from 20⁺⁰ weeks (as the timepoint requiring birth registration in Aotearoa New Zealand), although pēpi survival is only possible from 22-23 weeks. The mechanisms leading to spontaneous second trimester miscarriage (considered from 14⁺⁰ weeks gestation)¹ are similar to those causing spontaneous preterm birth. Therefore these two conditions (preterm birth and second trimester miscarriage) should be considered as the same pathophysiological entity with similar risk factors, risk modification, prediction and prevention. Due to the shared pathophysiological mechanisms and similar approaches to care, reference to spontaneous preterm birth in this section of Taonga Tuku Iho includes all births from 14⁺⁰ to 36⁺⁶ weeks.

Despite significant research efforts, there are no proven therapies to stop labour once it has established.¹ Prevention of spontaneous preterm birth, therefore, relies on the early prediction of those with a higher chance of preterm labour and/or PPROM. Identification of risk factors for spontaneous preterm birth allows for modification of risk where possible, and the use of additional evidence-based prediction measures and treatments prior to the onset of labour and/or PPROM, where they may effectively prevent preterm birth.

There are numerous established risk factors for spontaneous preterm birth, and many of these risk factors can be identified prior to, or in early pregnancy. However, additional risk factors may also develop during pregnancy. Identification of risk factors and their appropriate management relies on early engagement of wāhine/people in pregnancy care, usually with their Lead Maternity Carer (LMC) or primary care provider, along with clear pathways for obstetric referral where indicated.

Risk factors for spontaneous preterm birth may be considered to be:

• Directly modifiable – the risk factor can be removed or altered
• Indirectly modifiable – the risk factor cannot be taken away, but interventions are available to reduce risk
• Non-modifiable - the risk factor cannot be taken away or changed, but awareness may still be beneficial.

Wāhine/people with multiple major risk factors are likely to have a higher chance of spontaneous preterm birth compared to those with a single risk factor, with the magnitude of risk likely to be cumulative. However, it is noteworthy that even when several risk factors are identified, most wāhine/people will give birth at term.^2-7

The risk factors for spontaneous preterm birth are summarised in the table below. For this section, we have provided significant detail on the background to each risk factor which can be accessed here.

#Table 1: Risk factors for spontaneous preterm birth

Adjunct prediction tests for spontaneous preterm birth in the general population

Despite a wide variety of risk factors for spontaneous preterm birth, the majority of wāhine/people with one or more of these factors give birth at term, and some wāhine/people with none of these risk factors may still labour or experience PPROM before 37 weeks. Adjunct prediction tests have the potential to be used in combination with risk factor assessment, or alone, to identify those with a higher chance of spontaneous preterm birth, to allow resources and interventions to be used for those most likely to benefit.

These adjunct prediction tests for spontaneous preterm birth include ultrasound cervical length assessment and vaginal biomarker tests. This section focuses on their use in a general population without indirectly modifiable risk factors that may be modified through specialised preterm birth pregnancy care.

For those identified to have a high chance of spontaneous preterm birth (including second trimester miscarriage), due to factors that may be modified through specialised preterm birth pregnancy care, additional recommendations of practice for pregnancy care, including adjunct prediction tests, are provided in Prediction and prevention of spontaneous preterm birth in specialised preterm prevention care.

For wāhine/people with signs or symptoms of preterm labour (threatened preterm labour) and/or PPROM, recommendations of practice on the prediction and prevention of spontaneous preterm birth in these clinical scenarios, including adjunct prediction tests, are provided in Preterm prelabour rupture of membranes (PPROM) and threatened and active preterm labour.

#Recommendations and Practice

Guideline Recommendations (pink boxes) and Good Practice (yellow boxes) are provided as recommendations of practice. Comprehensive clinical oversight of māmā/person and pēpi wellbeing is required, and this may influence how these recommendations of practice are used.

Each recommendation of practice should be considered in consultation with wāhine/people and whanāu, including clear explanations to allow informed decision-making. Wāhine/people have the right to decline a recommendation of practice. In these circumstances, healthcare providers should follow their professional responsibilities for ongoing care. ^148,161-163

General population screening and risk identification for spontaneous preterm birth at pregnancy booking

All wāhine/people have a chance of preterm labour and/or PPROM, and some have a higher chance based on pre-existing risk factors or risk factors that develop during their pregnancy. Early identification of those with a higher chance of spontaneous preterm birth, allows for opportunity to modify risk, introduce preventative therapies and plan appropriate surveillance.

General population risk modification for spontaneous preterm birth at pregnancy booking

Once risk factors for spontaneous preterm birth have been identified, there is an opportunity to modify this risk, including directly treating and reducing that risk, introducing preventative therapies and planning appropriate additional surveillance and care.

General population screening and risk identification for spontaneous preterm birth during pregnancy

Wāhine/people may develop risk factors for preterm labour and/or PPROM during their pregnancy. Continued review and identification of these risk factors allows further opportunity to modify risk, introduce preventative therapies, plan appropriate surveillance and/or prepare wāhine/people and whānau for preterm birth.

General population risk modification for spontaneous preterm birth during pregnancy

As new risk factors for preterm labour and/or PPROM occur during pregnancy, there are opportunities to modify risk, introduce preventative therapies, plan appropriate surveillance and/or prepare wāhine/people and whānau for preterm birth.

#Auditable standards

#Included guidelines

The search identified 43 guidelines relevant to the prediction and prevention of spontaneous preterm birth for all wāhine/people, that met criteria for high-quality and/or were recommended for use with modifications.^105-147 This included eight guidelines on the general management of preterm labour where they included content on risk factors and/or prediction and prevention of spontaneous preterm birth),^105-112 seven on sexually transmitted infections,^{115-119,146,147} six on sepsis,^129-134 eight on smoking cessation,^135-142 three on vaccination,^126,127,143 two on maternal mental health,^120,128 one on healthy weight gain in pregnancy,¹⁴⁴ one on cervical surgery,¹²⁵ one on polyhydramnios,¹²¹ five on pregnancy screening,^{113,114,122-124} and one on guidelines for consultation.¹⁴⁵

Twelve of these guidelines were assessed to be high quality in both Rigour of Development (score >60%) and in Overall Assessment (score >60%), and were recommended for use in clinical practice by the Review Panel.^{111,115-117,122,123,125,128,129,134,142,143} Another seven were assessed to be high-quality in Overall Assessment (score >60%) only and were recommended for use in clinical practice by the Review Panel, or for use with modifications.^{113,119,124,126,130,136,147} A further 12 guidelines from local district health boards did not meet high-quality criteria, but were recommended for use with modifications by the Review Panel.^{105-110,112,121,131,132,135,137} The remaining 12 guidelines were from national, international or binational organisations and did not meet high-quality criteria, but were recommended for use with modifications by the Review Panel.^{114,118,120,127,133,138-141,144-146}

Multiple guidelines have been updated since the Review Panel evaluation, and where this has occurred, the updated guideline has been used. This is the case for the New Zealand Referral Guidelines for Consultation with Obstetric and Related Medical Services,¹⁴⁵ updated in 2026;¹⁴⁸ Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) guideline on measurement of cervical length for prediction of preterm birth,¹¹³ updated in 2021;⁹⁷ RANZCOG guideline on pre-pregnancy and pregnancy related vaccinations,¹²⁷ updated in 2023;¹⁴⁹ RANZCOG endorsed mental health care in the perinatal period,¹²⁸ updated in 2023;¹⁵⁰ RANZCOG guideline on screening in early pregnancy for adverse perinatal outcomes,¹²³ updated in 2024 to include preeclampsia only;¹⁵¹ the RANZCOG endorsed Royal College of Obstetricians and Gynaecologists (RCOG) guideline on maternal sepsis in pregnancy,¹²⁹ updated in 2024;¹⁵² International Society of Ultrasound in Obstetrics and Gynaecology (ISUOG) Practice guidelines for the routine mid-trimester fetal ultrasound scan,¹¹⁴ updated in 2022;¹⁵³ Society of Obstetric Medicine in Australia and New Zealand (SOMANZ) guideline on sepsis in pregnancy;¹³³ updated as a position statement in 2023;¹⁵⁴ New Zealand Sexual Health Society guideline on sexually transmitted infections,¹⁴⁶ updated in 2021;⁸⁶ New Zealand College of Midwives consensus statement on sexually transmitted infections,¹¹⁸ updated in 2025;¹⁵⁵ and World Health Organisation (WHO) guidelines for the treatment of Neisseria gonorrhoeae,¹¹⁷ chlamydia,¹¹⁶ and syphilis¹¹⁵ which have been amalgamated into a single updated guideline in 2024.¹⁵⁶ The 2019 Ministry of Health New Zealand Obstetric Ultrasound Guidelines¹²⁴ were also updated in 2024; it is still pending publication, however, the new recommendations (criteria for cervical length surveillance) have been used.

To support the preparation of this section, additional guidelines that were not identified by the original search were considered. The NHS England Saving Babies' Lives Care Bundle Version 3,¹⁵⁷ the United Kingdom Preterm Birth Network ‘Reducing Preterm Birth’ Guidelines for Commissioners and Providers,¹⁵⁸ and the Te Toka Tumai National Women’s Health Preterm Clinic Referral Guidelines¹⁵⁹ were included to support recommendations on criteria for specialist high-risk spontaneous preterm birth care. These guidelines were not included in the Review Panel assessment.

#Impact on equity

The vision of the Carosika Collaborative is ‘Equity in preterm birth outcomes will be achieved in Aotearoa by lowering preterm birth rates and optimising preterm birth care’ ; Taonga Tuku Iho is a major tool to support this. Equity has been prioritised throughout the development process of Taonga Tuku Iho and will drive its implementation and measurement of impact.

During the identification, evaluation and selection of the clinical practice guidelines that inform Taonga Tuku Iho, the Review Panel considered the potential impact on equity of recommendations within each guideline¹⁶⁰ and these are summarised here.

Review Panel guideline assessments identified that the recommendations in eleven of the 43 guidelines meeting criteria for consideration of inclusion in this guide had the potential to increase differences by equity factors,^{109,111,115,127,132,135,136,140,143,146,147} and 31 of the 43 had the potential to reduce differences by equity factors.^{105-111,114,116-118,120,122-125,128,135,137,138,142,143,146,147}

Important themes noted were equity of access to care, including for standard pregnancy care, with differences by ethnic group and region, with potential to improve access for Māori and those living rurally. In particular, the importance of improved consistency in early engagement and booking with a LMC was noted. The need for a national implementation plan was cited to ensure that resources, knowledge, skills and interventions for prediction and prevention of preterm labour and PPROM were consistently available, rather than dependent on local limitations.

Specific services were identified, including equitable access to mental health, pregnancy ultrasound, vaccination and sexual health services. It was noted that universal screening for sexual health may enable midwives to gain knowledge in these conversations and reduce stigma attached to sexually transmitted infection screening. Furthermore, some services would require directed support for specific populations, e.g. smoke change support for whānau Māori.

#Current research

The Candida in Pregnancy Study (CIPS), a randomised controlled trial, has assessed the impact of routine screening and treating asymptomatic Candida infection in pregnancy on spontaneous preterm birth. All participants were screened in early pregnancy, those that are culture positive for Candida, were randomised to active treatment with Clotrimazole or no treatment and the screening result was not revealed. The primary outcome is spontaneous preterm birth 20⁺⁰ – 36⁺⁶ weeks. It was funded by the Australian National Health Medical Research Council and has completed recruitment at sites across New South Wales, Australia. Results have been presented in abstract form, but peer-review publication is pending. ACTRN12610000607077.

The Australian Preterm Birth Prevention Alliance’s national multifaceted prevention programme¹⁰² has included a 21-month Breakthrough Series Collaborative. This involved 59 maternity hospitals across Australia participating in a clinician-led education programme, aiming to support local implementation of the national prevention programme. High-level results demonstrate a reduction in early-term birth, but no impact on preterm birth.¹⁰³ Due to the size of this study and varied approaches across hospitals and regions, additional exploration of data may identify specific aspects of care that will inform future spontaneous preterm birth care in Aotearoa.

#Statement on rationale for any differing recommendations from the high-quality guidelines

The mechanisms leading to spontaneous second trimester miscarriage (often referred to as second trimester loss) are similar to those causing spontaneous preterm birth and hence should be considered and managed in a similar way. To date, second trimester loss is often considered only for miscarriage ≥16⁺⁰ weeks. However, the gestational age to define the lower limit of the second trimester is conventionally considered to be after completion of 12 weeks. For Taonga Tuku Iho, we have elected to use ≥14⁺⁰ weeks to define second trimester miscarriage and to identify wāhine/people for inclusion in our recommendations. This conflicts with New Zealand Obstetric Ultrasound Guidelines¹²⁴ and Te Toka Tumai National Women’s Health Preterm Clinic Referral Guidelines,¹⁵⁹ that both refer to ≥16⁺⁰ weeks. We have adopted this gestation in accordance with the 2025 Mid-­trimester Pregnancy Loss Guideline Consensus Panel proposed global framework.¹⁶⁶

The criteria for referral for obstetric consultation due to indirectly modifiable risk factors have been developed using the New Zealand Obstetric Ultrasound Guidelines¹²⁴ (which identify recognised risk factors that warrant referral for cervical length surveillance) and Te Toka Tumai National Women’s Health Preterm Clinic Referral Guidelines,¹⁵⁹ with some adaptations. A single previous uterine instrumentation is associated with an increased chance of spontaneous preterm birth, and this is further elevated after 2-3 procedures.⁵ Te Toka Tumai National Women’s Health Preterm Clinic Referral Guidelines¹⁵⁹ include ≥2 uterine instrumentations in its referral criteria. The currently published New Zealand Obstetric Ultrasound Guidelines¹²⁴ does not include previous uterine instrumentation as a criterion (but it is included in the revised version, unpublished in January 2026). Taonga Tuku Iho has taken a pragmatic approach to use ≥3 uterine instrumentations in consideration of how the resources of specialist review and cervical length surveillance are utilised, and this is consistent with the Guidelines for Consultation with Obstetric and Related Medical Services (consultation code 3017).¹⁴⁸ The New Zealand Obstetric Ultrasound Guidelines¹²⁴ include ‘previous Caesarean section at full cervical dilatation’ in referral criteria, in Taonga Tuku Iho this has been expanded to ‘Previous caesarean section at advanced cervical dilatation and/or extensive tear through cervix +/- vagina without subsequent term birth’.

There is a lack of consensus amongst the included guidelines on universal cervical length screening at the mid-trimester scan. This topic continues to be debated internationally with significant variation in practice, as summarised in a recent comparative review of guidelines internationally.¹⁰⁰ Taonga Tuku Iho has adopted the recommendation that routine cervical length scanning at the time of the mid-trimester scan is not currently recommended in Aotearoa. This is based on Aotearoa-specific guidance in the New Zealand Obstetric Ultrasound Guidelines¹²⁴ and is consistent with the statement from Wāhi Rua, New Zealand Maternal Fetal Medicine Network (March 2022, published after the original search).¹⁶⁷ This differs from recommendations in the RANZCOG and ISUOG guidelines.^97,99

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