Preterm birth may happen because labour starts early or the waters break early (called spontaneous preterm birth) or it may be planned because staying pregnant is considered to be less safe for māmā and/or pēpi (called provider-initiated preterm birth, also known as iatrogenic preterm birth). Preterm birth is associated with a variety of factors, but there is not always a clear cause and often more than one thing contributes (multifactorial).

Spontaneous preterm birth      

Inflammation, infection and hormonal differences commonly contribute to spontaneous preterm birth. We can identify some conditions and situations that make the chance of a spontaneous preterm birth higher. These include:

• Previous spontaneous preterm birth or late miscarriage (after 16 weeks)
• Expecting twins, triplets or higher order multiple pregnancy
• Previous surgery to the cervix including LLETZ procedure and cone biopsy
• Urine infection, sexually transmitted infection or other systemic infections in pregnancy
• A congenital difference in the uterus and/or cervix such as bicornuate uterus or uterine didelphys
• Previous caesarean section performed when the cervix was fully dilated (10cm), especially if there was a uterine and/or cervical tear
• Smoking or other recreational substance use in pregnancy
• Heavy bleeding during pregnancy
• Previous multiple uterine instrumentations (≥2) including surgical termination of pregnancy, surgical management of a miscarriage
• Connective tissue disorders like Ehlos Danlos syndrome
• Poorly controlled diabetes in pregnancy

There are several ways in which some of these conditions and situations can be treated or modified to help prevent spontaneous preterm birth 

Many wāhine/people who have a spontaneous preterm birth do not have any of these conditions. This is why it is important that all pregnant wāhine/people know what preterm labour is and what signs and symptoms to look out for.

Provider-initiated preterm birth

There are several conditions that make the chance of a provider-initiated preterm birth higher because the māmā/person and/or pēpi becomes sick or is at risk of becoming sick. These include:

• Preeclampsia
• Fetal growth restriction
• Low-lying and/or stuck whenua/placenta or abnormal vessels in the membranes (placenta praevia, placenta accreta and vasa praevia)
• Heavy bleeding after 23 weeks (antepartum haemorrhage)
• Medical conditions in pregnancy such as diabetes, heart conditions, kidney problems

There are several ways to reduce the chance of developing these conditions in pregnancy and/or managing them to reduce the chance of needing to plan preterm birth.