Preterm birth is a significant problem that carries substantial morbidity and mortality. Treatment of preterm labor can prevent early birth. Antibiotic therapy has been used to prolong gestation in women with evidence of preterm labor through the probable mechanism of eradicating occult intrauterine infection. Thorp and associates performed a systematic literature search for evidence of the effectiveness of antibiotics in treating preterm labor.

Fourteen randomly controlled trials and one observational study met the criteria for inclusion in the study. The quality of each article was determined in terms of clarity of the study question, sampling strategy, clear measures of neonatal, birth, and maternal outcomes, and conclusions that were consistent with the outcomes.

Because the observational study had inconclusive results, only the 14 trials were analyzed. Birth-related outcomes that were evaluated included (1) estimated gestational age, (2) length of prolongation, and (3) delivery at term. Infant birth weight was also reviewed. One trial found improvement in all three birth-related outcomes, and five studies found no improvement in any of the three outcome measures. Four studies found significant pregnancy prolongation, and two studies noted a decreased proportion of preterm deliveries. A meta-analysis for each of the three outcome measures performed on the trials that offered appropriate data revealed that antibiotic treatment offered a marginally significant six-day increase in gestation and a 0.60-week increase in gestational age. Birth weight increased by a statistically significant 70 g. There were issues of probable heterogeneity and inconsistency among the study populations. Each study used a different antibiotic regimen. It is also unclear that the outcomes measured were statistically significant enough to result in improved perinatal outcomes.

The authors conclude that the literature evaluating the efficacy of antibiotic treatment for preterm labor is “fair” and supports the impression that this treatment prolongs pregnancy for only a short period in women with preterm labor. The effect of this benefit on perinatal morbidity and mortality is uncertain. There is no information about which antibiotic regimens are more effective. Women may benefit peripherally from antibiotic prophylaxis used to prevent group B Streptococcus sepsis in women with preterm labor. The authors call for more studies to examine the survival analysis rather than surrogate end points.