Objective: In an effort to elucidate possible causes of preterm labor, we undertook a prospective study of 50 patients consecutively admitted with intact membranes and preterm labor who eventually had a preterm delivery despite the use of tocolysis.
Study design: A comprehensive evaluation plan was instituted. This included a detailed history and physical examination, targeted ultrasonography, amniocentesis for Gram stain, culture, and glucose determination, laboratory analysis for infection (complete blood cell count, urinalysis, and cervical and urine cultures) and for antiphospholipid antibody syndrome (antinuclear antibody, lupus anticoagulant, anticardiolipin antibody), pathologic examination of the placenta, and a urine toxicology screen.
Results: The following groups of possible causes of preterm labor were identified: (1) faulty placentation, 50% (25/50); (2) intrauterine infection 38% (19/50); (3) immunologic factors, 30% (15/50); (4) cervical incompetence, 16% (8/50); (5) uterine factors, 14% (7/50); (6) maternal factors 10% (5/50); (7) trauma and surgery, 8% (4/50); (8) fetal anomalies, 6% (3/50); and (9) idiopathic conditions, 4% (2/50). Among the 50 patients two or more possible causes were identified in 58% (29/50).
Conclusion: We suggest that an exhaustive evaluation plan can identify possible causes in the majority (96%) of cases of "idiopathic" preterm labor that result in preterm delivery.