IVF success may depend on how long men abstain from ejaculation

Men should ejaculate less than 48 hours before in vitro fertilisation egg collection to maximise the chances of it leading to an ongoing pregnancy, according to the first clinical trial to test how different ejaculation abstinence intervals affect the success of the fertility treatment.

Towards the end of an IVF cycle, the woman takes a “trigger” drug that pushes developing eggs to maturation. This is injected 36 hours before the eggs are collected and fertilised.

To ensure the healthiest possible sperm for fertilisation, men are usually advised to ejaculate within a window of between two and seven days before providing the sample that will be used for IVF. “There is an optimal period between ejaculations when sperm are at their best,” says David Miller at the University of Leeds, UK, who wasn’t involved in the trial.

But two to seven days is a wide range. On the one hand, the longer sperm are stored in the testes, the longer they are exposed to various toxins, most notably free oxygen radicals, which are formed naturally during metabolic processes, and those from external factors such as pollution. This can cause DNA damage and impair sperm quality, says Richard Paulson at Keck School of Medicine of USC, Los Angeles, who also wasn’t involved in the trial. But too short a time between ejaculations reduces sperm numbers.

Until now, there hasn’t been any robust clinical data that shortening the ejaculation interval translates into improved pregnancy outcomes, but there have been hints. For instance, a 2024 meta-analysis found that leaving less than four days between ejaculations improved semen quality in men who are infertile. Another study reported that an interval of less than 4 hours reduced the amount of sperm that had DNA damage and improved sperm motility.

To test the idea directly, Yang Yu at First Hospital of Jilin University in Changchun, China, and his colleagues asked 226 men undergoing conventional IVF to ejaculate around 36 hours before producing their final sample. Another 227 were asked to ejaculate between 48 hours and seven days beforehand.

The group with the shorter abstinence interval had higher ongoing pregnancy rates – 46 per cent compared with 36 per cent. “The better pregnancy rate looks encouraging,” says Miller, “but of course, this doesn’t necessarily reflect fully, the final treatment outcome, which is live birth rate.” Nevertheless, he says that because the miscarriage rate was lower (although not statistically so) in the shorter abstinence group, he would expect more live births, too.

Paulson says that while the study makes an interesting observation, it has weaknesses, such as including both fresh and frozen embryos, when IVF success rates may vary between the two. He also points out that the data shows a decreased fertilisation rate but an increased number of ongoing pregnancies in the shorter abstinence group, suggesting fewer couples conceived, but of those who did, more continued past 12 weeks, which is something that needs more careful analysis. “This type of extraordinary claim would require extraordinary proof, with careful control of all possible factors,” he says.

Further research could also reveal whether frequent ejaculation improves pregnancy outcomes for couples not having IVF. “This trial is a nice proof that a shorter abstinence is a good way of having better sperm,” says Jackson Kirkman-Brown at the University of Birmingham, UK.