Fig. 2.

Salivary progesterone profiles in conception and ovulatory nonconception cycles in women from Chicago and rural Bolivia (days 1-28). Ovulatory cycles are aligned on the first day of the subsequent cycle, and days are numbered backward; conception cycles are aligned on the putative day of ovulation and numbered accordingly. Progesterone levels in ovulatory cycles are significantly lower in women from Bolivia than in women from Chicago throughout the ovarian cycle, and also lower during and subsequent to ovulation in conception cycles.