In a selected population of 312 women, prospective menses records were maintained during the autumn of 1977. Women whose menstrual cycle duration approaches the cycle duration of the earth's moon (29.5 days) tend to ovulate in the dark phase of the lunar period. The dark phase encompasses the half-cycle of the month from last quarter, through new moon, to first quarter. Women showing irregular menses also tended to ovulate during the dark phase of the lunar period.
PIP: The possibility of a lunar effect on the menstrual cycle was investigated in 312 university students who kept records of their menstrual cycles. These records were studied for 14 weeks in a double-blind, prospective manner. Of the 312 women, 68 experienced lunar period cycles (29.5 days). Of these 68, 47 menstruated in the light half of the month; therefore, ovulation tended to occur in the dark phase of the lunar period which is defined as the half-cycle of the month from the last quarter, through new moon, to first quarter. Even women with irregular menses (defined for this study as appreciably varied from the 29.5-day lunar cycle) also tended to ovulate during the dark phase of the lunar period. One possible explanation is that a natural rhythm of electromagnetic radiation has its origin in the lunar cycle and may be reflected in phase-locking of the human menstrual cycle.