The normal variabilities of the menstrual cycle.

OBJECTIVE: To address conflicts in the normal variabilities of the menstrual cycle using the newest generation test methods and to establish normal ranges for use in clinical practice.
DESIGN: Daily urine samples were collected from 167 women eager to achieve pregnancy. Samples were tested prospectively for LH and total hCG. A total of 458 nongestational and 111 gestational menstrual cycles were evaluated.
SETTING: Division of Women's Health Research, University of New Mexico. PATIENT(S): One hundred sixty-seven women desiring pregnancy. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Levels of hCG and LH. RESULT(S): Menstrual cycles were 27.7 +/- 2.4 days in length. The LH peak indicated the onset of the presumed ovulatory window, which occurs at 14.7 +/- 2.4 days. Implantation (first day of sensitive detection of hCG) occurred in gestational menstrual cycles at 24.6 +/- 3.1 days, or 4.3 +/- 2.2 days before missing the expected onset of menses. CONCLUSION(S): Our data confirm epidemiological studies on menstrual cycle length and variability and hormonal studies on timing of the ovulatory window and its variability. They dispute, however, the published data on the timing and variance of implantation. As shown, implantation is limited to a 10-day interval culminating in the day of the expected onset of menses. Reference range data provide guidelines for differentiating normal and problem menstrual cycles.