Objective α1-Antitrypsin (AAT) is protective of tissue damage induced by enzymes of inflammatory cell source. Inflammatory cells are involved in preterm labor, preterm premature rupture of membrane (PPROM) and term premature rupture of membrane (PROM). The purpose of this research was to examine whether plasma concentration and activity of AAT differ between these manifestations. Methods In a prospective case control study, blood samples were assayed for AAT concentration and activity in 71 individuals. AAT concentration and activity were measured by standard methods. Results No significant differences were found between AAT levels (p = 0.497) and activity (p = 0.879) in preterm and term labor. AAT levels and activity in PPROM and PROM were not significantly different as well (p = 0.748 and p = 0.880, respectively). While 69 out of 71 patients displayed normal circulating levels of AAT, 2 PPROM patients out of 15 had abnormally low, previously undiagnosed,AAT concentrations, and had subsequently developed complications that were absent in the other groups. Conclusions No statistically significant differences were demonstrated in the levels of AAT between patients with preterm and term labor, nor between preterm and term PROM. Yet, unexpectedly, patients that had marked AAT deficiency belonged exclusively to the PPROM group.