Proportion of Women with Symptomatic Preterm Labor Who Deliver Preterm vs Term
Approximately 50% of women with symptomatic preterm labor ultimately deliver preterm, while the other 50% go on to deliver at term. 1
Understanding Preterm Labor and Delivery Outcomes
Preterm labor is a significant obstetrical concern that affects many pregnancies. According to the American College of Obstetricians and Gynecologists (ACOG), preterm labor precedes approximately 50% of all preterm births 1. This statistic is particularly important as it indicates that not all women who experience symptoms of preterm labor will ultimately deliver preterm.
Key Statistics:
- Preterm birth occurs in approximately 12% of all live births in the United States 1
- Preterm labor precedes about 50% of these preterm births 1
- This means that many women who experience symptomatic preterm labor will continue their pregnancy to term
Risk Factors and Predictors
Several factors may influence whether a woman with symptomatic preterm labor will deliver preterm or continue to term:
- Threatened preterm labor: Women with threatened preterm labor have a significantly higher risk (OR 2.91,95% CI 1.57-5.40) of delivering preterm 2
- Twin and multiple pregnancies: These carry a significantly greater risk of preterm birth, with up to 76% of twin pregnancies resulting in preterm delivery in some studies 2
- Intrauterine infection: At least 40% of preterm births are associated with intrauterine infection, which triggers inflammatory cascades that can lead to uterine contractions and membrane rupture 3
Management Implications
Understanding the proportion of women who progress from symptomatic preterm labor to preterm delivery has important clinical implications:
- Activity restriction: Contrary to traditional practice, evidence suggests that activity restriction does not reduce preterm birth rates in women with threatened preterm labor. In fact, some studies show that women prescribed activity restriction had higher rates of preterm delivery (37.1% vs 14.3%) 2
- Antenatal corticosteroids: The Society for Maternal-Fetal Medicine recommends careful selection of candidates for late preterm corticosteroids who are likely to deliver preterm, as approximately 16.4% of women in the ALPS trial who received steroids for threatened preterm labor ultimately delivered at term 2
Clinical Relevance
The fact that approximately 50% of women with symptomatic preterm labor will deliver at term has significant implications for clinical decision-making:
- It highlights the challenge of accurately predicting which women with preterm labor symptoms will actually deliver preterm
- It emphasizes the importance of judicious use of interventions such as tocolytics, corticosteroids, and hospital admission
- It suggests that many women may be unnecessarily exposed to medications and interventions that carry potential risks
Conclusion
The evidence indicates that symptomatic preterm labor results in preterm delivery in approximately 50% of cases, with the remainder continuing to term. This underscores the difficulty in accurately predicting preterm birth and highlights the need for improved diagnostic tools to better identify women who will truly deliver preterm.