Prevention of Preterm Birth

Jeffrey M. Denney; Jennifer F. Culhane; Robert L. Goldenberg

Disclosures

Women's Health. 2008;4(6):625-638. 

In This Article

Abstract and Introduction

The preterm birth rate in the USA is nearing 13%. The recent rise has been attributed to increased indicated preterm births and multiple births following artificial conceptions. There are few obstetrical interventions that successfully delay or prevent spontaneous preterm birth or reduce the risk factors leading to indicated preterm birth. On the other hand, there are many strategies that have improved outcomes for those infants who are born preterm. These include the use of corticosteroids for fetal maturation and regionalization of perinatal care for high-risk mothers and their infants. Several interventions, including progesterone use and cerclage, demonstrate promise in reducing spontaneous preterm births. The most pressing need is to better define the populations of pregnant women for whom these and other interventions will effectively reduce preterm birth.

In developed countries, preterm birth is the leading cause of perinatal mortality as well as morbidity.[1] As much as two-thirds of the perinatal mortality and a half of long-term neurologic disabilities, including cerebral palsy, are associated with a preterm birth. Infants are born preterm following spontaneous labor with intact membranes (~45% of cases), preterm membrane rupture (~30%) and after labor induction or cesarean delivery for maternal or fetal indications (~25%).[1,2] The frequency of preterm birth is approximately 12.7% in the USA and 4.4-8.2% in many other developed countries, such as Australia, New Zealand, Sweden and Japan.[3,4,5] The rate of preterm birth has increased in many locations, predominantly because of increasing indicated preterm births and preterm delivery of artificially conceived multiple pregnancies.[6,7,8] Although all births before 37 weeks' gestation are classified as premature, births occurring prior to 32 weeks' gestation (~2% of all births) account for most neonatal deaths and long-term handicaps.[9]

Common reasons for indicated preterm births include pre-eclampsia/eclampsia and intrauterine growth restriction.[10,11] Births following spontaneous preterm labor and spontaneous preterm premature rupture of the membranes (pPROM) - together called spontaneous preterm births - are considered a syndrome caused by multiple etiologies, including infection/inflammation, vascular disease, uterine overdistension and immunological disorders.[1] Important risk factors for spontaneous preterm birth include Black race, low socioeconomic status, short interpregnancy interval, periodontal disease and maternal thinness.[1] By far, a woman's most significant risk factor is having a history of a prior preterm birth.[12] A short cervical length diagnosed by ultrasound and an elevated cervical-vaginal fetal fibronectin concentration are the strongest medical-test predictors of spontaneous preterm birth.[13,14] It is apparent that different causes and predictors are more common or have a stronger relationship with preterm birth at various gestational ages. For example, infection is by far the most common cause of preterm birth at less than 30 weeks, but plays a less important role nearer to term.[15] Similarly, a positive cervical-vaginal fetal fibronectin test is a much stronger predictor of preterm birth at 24 weeks than a positive test later in pregnancy.[13,14]

Preterm birth is consequential, predominantly because it results in morbidity or death in some infants. Preterm babies are at increased risk for death when compared with their term counterparts. However, preterm birth is of lesser consequence if the infant does not have any acute or long-term disorders or experiences a prolonged hospitalization and is sent home with the parents. It should also be noted that some full-term infants may die or exhibit evidence of neurologic damage as a result of problems occurring later in the pregnancy. Thus, although delaying birth would be desirable in the majority of situations, there are cases in which facilitating a preterm delivery, whether by induction or cesarean, may lead to improved maternal and neonatal outcomes.

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