Objective: To test whether maternal corticotrophin-releasing hormone levels are elevated in the mid- trimester for those women who subsequently had spontaneous preterm delivery and to assess the clinical utility of the measurement in the prediction of preterm delivery.
Design: A prospective observational study.
Setting: Department of Obstetrics and Gynaecology, Prince of Wales Hospital, Hong Kong.
Population: 1047 low risk pregnant women recruited at 15-20 weeks of gestation.
Methods: Venous samples were assayed for levels of corticotrophin-releasing hormone. The investigators responsible for the laboratory assay were blinded to the obstetric outcome.
Main outcome measures: Incidence of preterm, term and post-term pregnancies.
Results: Those who were delivered spontaneously at a preterm gestational age (before 34 weeks) had significantly higher corticotrophin-releasing hormone levels in the mid-trimester, compared with those who were delivered at term or post-term. There was a trend towards lower corticotrophin-releasing hormone levels with more advanced gestational age at delivery. When the measurement of corticotrophin- releasing hormone was used to predict delivery before 34 weeks, the best cut off was 1.9 MoM, which produced a sensitivity of 72.7% and specificity of 78.4%. This translated to a positive predictive value of 3.6%, negative predictive value of 99.6% and relative risk of 9.4 when the background prevalence of spontaneous preterm delivery before 34 weeks was 1.1%. The likelihood ratio was 3.4.
Conclusions: Mid-trimester maternal corticotrophin-releasing hormone levels are elevated in pregnancies destined to deliver preterm before 34 weeks. When used alone in a low risk population, the measurement has a low predictive power for preterm delivery. However, the likelihood ratio of 3 4 implies that in high risk populations the test may be considerably more valuable.