Harbert G M, Cornell G W, Thornton W N
Science. 1970 Oct 2;170(3953):82-5. doi: 10.1126/science.170.3953.82.
Diurnal variations in the average intrauterine pressure and in the average frequency of contraction were demonstrated in four nonpregnant rhesus monkeys. Uterine activity is lowest between 0400 and 0700 hours and highest between 1400 and 1700 hours. There is statistically significant correlation between uterine activity and diurnal variation in core temperature.
