Individual patient data meta-analysis on preterm birth risk in asymptomatic pregnant individuals with prior spontaneous preterm birth

OBJECTIVE: Pregnant patients with a previous spontaneous preterm birth are at high risk for recurrent (spontaneous) preterm birth. We investigated whether the number of previous spontaneous preterm births, gestational age of the previous birth and cervical length could stratify patients into different risk groups for recurrence to investigate whether there is a risk group that does not require additional interventions. DATA SOURCES: A systematic search of MEDLINE and EMBASE was conducted from 1995 until April 2025. STUDY ELIGIBILITY CRITERIA: Studies that were included were prospective studies with original individual patient data available that reported on asymptomatic pregnant individuals with ≥1 previous spontaneous preterm births at <37 weeks' gestation for whom cervical length had been measured between 18 and 24 weeks' gestation and who did not receive any preventative treatment for recurrent spontaneous preterm birth. METHODS: A pooled analysis of individual patient data was performed including assessment of the associations among cervical length, obstetrical history, and recurrent spontaneous preterm birth. RESULTS: We included data from 1316 patients (7 data sets). The preterm birth rates of the current pregnancy before 32, 34, and 37 weeks' gestation were 9.1%, 14%, and 31% respectively. Cervical length and gestational age of the earliest previous spontaneous preterm birth and gestational age of the most recent previous delivery contributed independently to the risk for recurrent preterm birth and can be used to stratify the recurrence risk. The incidence of total preterm birth among patients with a previous spontaneous preterm birth before 24 weeks' gestation and a current short cervical length of <15 mm was as high as 50% (95% confidence interval, 12-88) for delivery <32 weeks' gestation and 67% (95% confidence interval, 22-96) for delivery <37 weeks' gestational age. In the lowest risk group (earlier previous spontaneous preterm birth between 32+0 and 36+6 weeks' gestational age and cervical length of >30 mm in their current pregnancy), the rates for total preterm birth before 32, 34, and 37 weeks' gestational age were 3.9% (95% confidence interval, 1-8), 9.8% (95% confidence interval, 6-16), and 23% (95% confidence interval, 19-32), respectively. Low-risk references groups had spontaneous preterm birth rates of 1.5%, 1.3% to 2.6%, and 4.9% to 10.5% before 32, 34, and 37 weeks of gestation, respectively. CONCLUSION: Independent of cervical length or gestational age of the previous spontaneous preterm birth, all patients with a history of spontaneous preterm birth retain an increased risk for recurrence of preterm birth at any gestational age. Even patients with the lowest risk still have a higher risk than those without a previous spontaneous preterm birth. Therefore, counselling and surveillance for preventative treatments remain essential in managing these patients.