an increasing trendP < 0.001
In contrast, the average menstrual cycle length exhibited an increasing trend ( P < 0.001, P -trend < 0.001), while both the average number of menstrual periods per year and the number of ovulatory cycles showed significant decreasing trends ( P < 0.005, P -trend < 0.005), with the Q4 group being significantly lower than the Q1 and Q2 groups.