Preterm birth is a ubiquitous yet mysterious phenomenon. Preterm birth, defined as birth prior to 37 weeks’ gestation, is now the primary worldwide cause of morbidity and mortality in the newborn period and the top cause of child mortality among those younger than 5 years, accounting for 1 million deaths every year.1 Nevertheless, it remains poorly understood.
Spontaneous preterm birth is a syndrome characterized by labor that starts too soon. It is distinguished from medically indicated preterm birth, in which labor induction or operative delivery are performed to protect the health of the fetus or mother. Preterm labor is not the same as labor at term—except that, in the end, it also results in the altered physical behavior of the uterus (regular contractions) and changes in the cervix (effacement and dilatation) that lead to rupture of amniotic membranes and expulsion of a fetus.2 Unlike term labor, preterm labor is associated with pathologic activation of these labor processes by 1 or multiple mechanisms of disease, such as infection or inflammation.1 No matter what the factors associated with preterm birth might be, the specific nature of their perturbation(s) or their cause(s), or in what field they are identified (eg, psychology, sociology, or economics), they all must ultimately translate into measureable biological phenomena that have the ability to initiate or accelerate the physiology that characterizes parturition, which is largely immunologic in nature.
Wallenstein MB, Shaw GM, Stevenson DK. Preterm Birth as a Calendar Event or Immunologic Anomaly. JAMA Pediatr. 2016;170(6):525-526. doi:10.1001/jamapediatrics.2016.0213