Premature birth occurs when a baby is born before 37 completed weeks of pregnancy, rather than the typical 40 weeks for a full-term birth. Premature births are categorized by gestational age: extremely preterm (less than 28 weeks), very preterm (28 to less than 32 weeks), and moderate to late preterm (32 to 37 weeks). Premature birth is a significant global health concern, with 13.4 million babies born prematurely in 2020. Complications are a leading cause of death among children under five.
Likelihood of Recurrence
A previous premature birth significantly increases the chance of recurrence. While the risk is elevated, the majority of subsequent pregnancies still result in a full-term birth.
The likelihood of recurrence is influenced by the gestational age of the prior birth; earlier births carry a higher risk. For instance, a woman who delivered her first baby between 24 and 28 weeks has approximately a 40 percent chance of delivering early in her next pregnancy. Overall, after a spontaneous preterm birth, the risk of it happening again in a subsequent pregnancy is around 22% to 31%.
Factors Influencing Future Premature Birth
Several factors can influence the likelihood of a future premature birth, ranging from a woman’s previous obstetric experiences to specific medical conditions and lifestyle choices.
A history of prior preterm deliveries is a significant indicator; the risk increases with the number of previous preterm births and if the prior delivery occurred at an earlier gestational age. For example, a first pregnancy before 32 weeks substantially increases the risk for subsequent births before 32 weeks.
Maternal medical conditions also play a role. Cervical insufficiency, where the cervix dilates too early, can lead to preterm birth. Uterine anomalies, like a unicornuate or bicorniate uterus, are associated with higher risk due to abnormal shape. Chronic conditions such as diabetes and hypertension also increase risk. Certain infections, like bacterial vaginosis, have been linked to increased preterm delivery risk.
Lifestyle and environmental factors can also contribute. Smoking, substance use, and a short interpregnancy interval—less than 18 months between pregnancies—are associated with an increased risk of premature birth. For instance, a short interpregnancy interval (less than six months) has been linked to a higher risk of preterm birth, including very preterm birth. Multiple gestations, such as twins or triplets, inherently carry a higher risk of preterm birth.
Managing Risk in Subsequent Pregnancies
For women with a history of premature birth, managing risk in subsequent pregnancies involves a combination of medical strategies and lifestyle adjustments.
Pre-conception counseling with a healthcare provider is important to discuss individual risks and develop a personalized plan before conceiving again. This allows for assessment of pre-existing health issues, like diabetes or hypertension, ensuring they are well-controlled.
Medical interventions help reduce recurrence risk. Progesterone supplementation, administered vaginally or by injection, can prevent recurrent preterm birth in high-risk women, prolonging pregnancy and improving fetal outcomes. Cervical cerclage, a surgical procedure reinforcing the cervix, may be considered for cervical insufficiency. Close monitoring, including serial cervical length measurements via transvaginal ultrasound, can identify cervical shortening for timely intervention.
Lifestyle adjustments also reduce premature labor risk. Avoiding smoking, illicit drug use, and excessive alcohol consumption is important due to links with adverse birth outcomes. Maintaining a healthy weight, adopting a nutritious diet, and managing stress support a healthy pregnancy. Early and consistent prenatal care enables identification and management of potential issues. Prompt treatment of underlying chronic conditions or infections further contributes to a healthier pregnancy.