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Determinants of preterm delivery in low-risk pregnancies. The RADIUS Study Group
B L Harlow1, F D Frigoletto, D W Cramer
1Obstetrics and Gynecology Epidemiology Center, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
Journal of Clinical Epidemiology
|April 1, 1996
Summary
Unknown factors contribute significantly to preterm birth in low-risk pregnancies, particularly for first-time mothers. Known risk factors explain only a small portion of spontaneous preterm deliveries.
Area of Science:
- Obstetrics and Gynecology
- Perinatal Epidemiology
- Maternal-Fetal Medicine
Background:
- Preterm delivery remains a leading cause of neonatal morbidity and mortality.
- Identifying risk factors for spontaneous and medically induced preterm birth in low-risk populations is crucial for targeted interventions.
- Previous studies have focused on high-risk pregnancies, leaving a gap in understanding low-risk scenarios.
Purpose of the Study:
- To determine the incidence and attributable risks of characteristics associated with spontaneous and medically induced preterm delivery in low-risk singleton pregnancies.
- To quantify the proportion of preterm births explained by known risk factors versus unknown factors in this population.
- To identify specific demographic, clinical, and lifestyle factors contributing to different preterm delivery mechanisms.
Main Methods:
- Analysis of data from 14,948 low-risk singleton pregnancies.
- Calculation of incidence, risk ratios, and population-attributable risk percents (PAR%) for various risk factors.
- Stratification of analysis by preterm delivery mechanism: spontaneous labor, premature rupture of membranes (PROM), and medical intervention.
Main Results:
- The overall incidence of preterm birth was 50.4 per 1000 deliveries.
- Unknown factors associated with first live birth accounted for the largest fraction of prematurity (PAR% 16.0-30.5%).
- For spontaneous preterm labor, fetal sex (male) was a significant factor (PAR% 13.6%). For PROM, maternal age >30 and positive urine culture were notable (PAR% 7.9 and 6.7, respectively).
- For medically induced preterm birth, maternal pre-pregnancy weight >150 lbs (PAR% 23.8), prenatal urine protein (PAR% 18.7%), and first-trimester smoking (PAR% 8.6%) were key contributors.
Conclusions:
- Known risk factors explain a limited proportion of spontaneous preterm delivery incidence in low-risk pregnancies.
- First live birth, fetal sex, maternal age, urine abnormalities, pre-pregnancy weight, and smoking are associated with different preterm birth mechanisms.
- Further research is needed to elucidate the unknown factors contributing to preterm birth in low-risk populations.