Seasonal Influence of Diurnal Rhythms in the Onset of the Plasma Luteinizing Hormone Surge in Women

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Abstract
The time of the LH surge onset in plasma was detected in 75 human cycles. The preovulatory LH surge began between midnight and 0730 h in two thirds of the patients. According to the season of study, the LH surge began between 1030 and 2215 h in 52.4% of the spring cycles compared with 12.9% of the cycles studied during other seasons (p < 0.001). The highest frequency of the LH surge occurrence over a 3-h time interval was 1500 ± 1.5 h during the spring cycles (28.6%) and 0300 ± 1.5 h (42.5%) during the other seasons. It was estimated that ovulation occurred primarily in the morning during the spring and primarily in the evening during autumn and winter.