INFLUENCE OF GESTATIONAL-AGE ON THE TIME FROM SPONTANEOUS RUPTURE OF THE CHORIOAMNIOTIC MEMBRANES TO THE ONSET OF LABOR

Our goal was to assess the influence of gestational age on the timing of labor onset following spontaneous rupture of the chorioamniotic mem branes. The 24,831 patients in the Nova Scotia Atlee perinatal databas e from 1986 to 1992 whose membranes ruptured prior to labor onset and had live births were analyzed using life-table analysis methods. The p robability of labor onset at specified intervals following rupture was markedly lower when rupture occurred earlier in gestation. Pregnancie s of <33 weeks' gestation were less than half as likely as term pregna ncies to proceed to labor within 24 hours and pregnancies of 33-36 wee ks' gestation were 50-75% as likely as term pregnancies to progress wi thin that period. These data provide clear evidence that the earlier i n gestation the rupture occurs, the less likely labor onset is within specified time periods. This pattern supports the contention that pret erm rupture of membranes is etiologically distinct from preterm labor.