ANTENATAL PATTERNS OF UTERINE ACTIVITY IN LOW-RISK WOMEN - A LONGITUDINAL-STUDY

There is a surprising lack of information on antenatal patterns of ute rine activity in the normal obstetric population, with the majority of research having focussed on women at high-risk for preterm birth. We conducted a prospective longitudinal study to investigate patterns of uterine activity in women with singleton gestations at low-risk for pr eterm birth. Twenty pregnant women were recruited and their uterine ac tivity was recorded using ambulatory tocodynamometry twice weekly thro ughout the latter half of pregnancy. The collected data were transmitt ed to a central receiving station for analysis. As gestation advanced there was a progressive increase in the median number of contractions detected per hour, peaking and stabilizing at 37-40 weeks (median of 0 contractions/hour at 20-24 weeks rising to 5.4 contractions/hour at 3 7-40 weeks). In those women with uterine activity, contraction duratio n and amplitude of deflection significantly increased as gestation adv anced. There was a progressive increase in the number of higher amplit ude contractions throughout the third trimester. Increasing parity was not associated with increasing antenatal uterine contraction frequenc y. No association between normal daily physical activity and uterine c ontraction frequency was evident throughout gestation. In normal human pregnancy there is a steady, progressive increase in the frequency, d uration and amplitude of antenatal uterine activity throughout the lat ter half of gestation, The uterine contractile profile alters from one of a low amplitude, low frequency pattern in the second trimester to a higher amplitude, higher frequency pattern at term.