Objective: Patients with an episode of preterm labor that subsides in response to tocolysis and who, subsequently, deliver at term are considered to have false preterm labor. However, the episode of "preterm labor" may represent the uterine response (ie, uterine contractions) to an insult not severe enough to trigger preterm parturition, but which may put the fetus at risk for additional pregnancy complications, including growth restriction. The objective of this study was to compare the frequency of small-for-gestational-age (SGA) neonates among patients with an episode of increased uterine contractility who delivered at term and those who delivered preterm.
Study design: This retrospective cohort study included 849 patients. Inclusion criteria were (1) regular uterine contractions that required hospitalization, (2) intact membranes, and (3) gestational age between 20 and 36 weeks. SGA was defined as a birth weight of <10th percentile for gestational age. Placental pathologic evidence was reviewed, and the results were used to classify patients into an inflammatory cluster, vascular cluster, or both. Contingency tables, Mann-Whitney U test, and multivariate logistic regression were used for statistical analyses. A probability value of <.05 was considered significant.
Results: The prevalence of SGA neonates in the study population was 16.1% (124/772). Patients who delivered at term had a significantly higher frequency of SGA neonates than those who delivered preterm (21.5% [64/298] vs 12.7% [60/474]; P = .001); the results of placental pathologic evidence were available in 63.7% (492/772) of the patients. Patients who delivered at term had a higher frequency of fetal or maternal vascular lesions without histologic evidence of inflammation than those who delivered preterm (29.1 % [43/148] vs 18.9% [65/344]; P = .01). Term delivery after an episode of regular preterm uterine contractions was associated with an odds ratio of 2.22 (95% CI, 1.28-3.85) to deliver an SGA neonate after the statistics were controlled for confounding variables. A subanalysis limited to patients who received tocolysis showed similar results.
Conclusion: Patients with an episode of increased uterine contractility that subsided and who deliver at term are at risk for delivering an SGA neonate, which suggests that an episode of false preterm labor is not a benign condition. We propose that insults to the fetoplacental unit may be resolved by either irreversible preterm parturition or restriction of fetal growth.