Preterm labor

Preterm labor can be caused by various factors and occurs between 24 and 37 weeks' gestation. Spontaneous preterm labor is often associated with infection and inflammation, particularly at early gestations. Only a minority of women who present with preterm contractions progress to actual labor and delivery.

Risk factors include previous preterm labor, cervical surgery, urinary tract infections, previous emergency cesarean section, and multiple (multifetal) pregnancies. Bleeding and premature rupture of membranes at any gestation is associated with higher rates of preterm delivery.

Early spontaneous birth can be predicted using serial digital examination or transvaginal ultrasound of the cervix. Fetal fibronectin detected in cervico-vaginal secretions can also be used. Combining cervical ultrasound and fetal fibronectin gives the best prediction of progression to preterm birth.

Effective prophylactic interventions have not been identified. Cervical cerclage has a limited role in high-risk women, and progesterone therapy may be of benefit. Few lifestyle interventions improve outcome, but cessation of smoking is recommended.

In utero transfer to appropriate neonatal facilities and prenatal corticosteroids reduce perinatal mortality and morbidity. Tocolytic agents are used in some patients to prevent birth in the short term, in order to achieve in utero transfer and allow corticosteroid administration. Longer-term use of tocolysis is not established as an effective intervention.

There is no internationally recognized definition of preterm labor. Preterm birth occurs between 24 and 37 weeks' gestation. However, infants can now survive from as early as 22 weeks’ gestation.[1]Mactier H, Bates SE, Johnston T, et al. Perinatal management of extreme preterm birth before 27 weeks of gestation: a framework for practice. Arch Dis Child Fetal Neonatal Ed. 2020 May;105(3):232-9. https://fn.bmj.com/content/105/3/232.long http://www.ncbi.nlm.nih.gov/pubmed/31980443?tool=bestpractice.com ​ In two-thirds of cases, preterm birth occurs following spontaneous onset of labor.[2]Romero R, Dey SK, Fisher SJ. Preterm labor: one syndrome, many causes. Science. 2014 Aug 15;345(6198):760-5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4191866 http://www.ncbi.nlm.nih.gov/pubmed/25124429?tool=bestpractice.com ​ Only a minority of women who present with preterm contractions known as threatened preterm labor (TPTL) progress to actual labor and delivery. The remainder of preterm birth is due to iatrogenic delivery, most commonly because of preeclampsia and intrauterine growth restriction. Preterm prelabor rupture of membranes (PPROM) is defined as the rupture of membranes at <37 weeks' gestation and prior to the onset of labor. This topic will focus on the management of spontaneous preterm labor that may follow TPTL or PPROM.