Characteristics of uterine activity in gestations less than 20 weeks.

Ambulatory tocodynamometry has been used for some time to record uterine activity during pregnancy. Most studies, however, have been performed in the third trimester (more than 24 weeks). The current study was initiated to assess uterine activity at earlier gestational ages. One hundred thirty-seven patients were studied between 14-19 weeks' gestation (inclusive). Seven patients who were being monitored were noted to have preterm labor, and six of these seven were found to have increased uterine activity before the diagnosis of preterm labor. There was no difficulty encountered in the vast majority of cases in recording objective, accurate uterine activity information even at these early gestational ages. There was an increase in the uterine activity (during the 18th and 19th weeks) in patients destined to develop preterm labor later in gestation as compared with the contraction pattern of those who labored at term. This study demonstrates that accurate uterine activity information can be gained at these early gestational ages and that when increased contraction frequency is present, it is related to preterm labor.