Contraceptive efficacy: Determining the threshold for effective suppression based on sperm concentration, motility,...

Area of Science:

• Reproductive endocrinology and male fertility

Background:

• Human spermatogenesis involves complex hormonal regulation by testosterone and follicle-stimulating hormone (FSH).
• Hormonal contraceptives suppress key reproductive hormones, leading to reduced sperm production.

Purpose of the Study:

• To evaluate the efficacy of hormonal contraception in suppressing sperm concentration for male fertility control.
• To discuss the implications for developing new contraceptive agents and assessing sperm parameters.

Main Methods:

• Review of clinical trials using testosterone-based hormonal contraceptives.
• Analysis of sperm concentration, motility, and morphology data in relation to contraceptive efficacy.
• Assessment of current and emerging methods for monitoring sperm parameters.

Main Results:

• Suppression of sperm concentration to ≤1 million/mL with hormonal contraceptives is effective in preventing pregnancy.
• Sperm motility and morphology measurements become difficult and potentially unnecessary at very low sperm concentrations.
• Establishing definitive thresholds for sperm motility or morphology for conception prevention is not currently possible.

Conclusions:

• Effective male contraception relies on suppressing sperm output to very low levels.
• New contraceptive agents may require different efficacy benchmarks based on their mechanism of action.
• Validated laboratory semen analyses are crucial for monitoring contraceptive efficacy, and caution is advised with unvalidated at-home tests.