DIURNAL AND GESTATIONAL PATTERNS OF UTERINE ACTIVITY IN NORMAL HUMAN-PREGNANCY

Objectives: To define the profile of 24-hour uterine activity in norma l pregnancy and to correlate contraction frequency with physical activ ity and emotional stress diaries. Methods: One hundred nine low-risk p regnant women who delivered at term recorded uterine contractions for 24 hours twice weekly from 20-40 weeks' gestation using an ambulatory monitor and kept a physical activity and emotional stress diary. Contr actions per hour were calculated for each hour of the day and week of gestation, and related to physical activity and emotional stress. Resu lts: We analyzed 71,683 hours. No contractions were recorded in 73% of the hours, and fewer than four contractions per hour occurred in 96%. Significant inter-individual variability was noted. Contractions incr eased markedly with gestational age: The 95th percentile was 1.3 contr actions per hour at 21-24 weeks, 2.9 at 28-32 weeks, and 4.9 at 38-40 weeks. A strong clustering of contractions occurred at night, which be came pronounced after 24 weeks (night:day ratio 2:1 at 28-32 weeks). T o adjust for the effects of gestational age and time of day, contracti ons per hour were converted to gestation- and hour-specific percentile s (''contraction percentiles''). Rest was associated with a fall in co ntraction percentile by 1.25, whereas coitus increased the contraction percentile by 5.52 (P < .05). No changes were noted with emotional st ress. Conclusions: This study provides normative contraction data in u ncomplicated pregnancy. A strong diurnal rhythm is present from 24 wee ks onward, with 67% of contractions occurring at night. Contractions p er hour increase with gestational age but rarely exceed three per hour before term. Rest and sexual activity have small but measurable effec ts on contraction frequency.