Here is the exact amount of sleep you need for successful sperm

Sleep your way to strong sperm: Snoozing for 7 to 8 hours a night seems to be the best range for sperm health, a preliminary study in the journal Fertility & Sterility suggests.

After analyzing the lifestyle habits of nearly 700 couples for one year, the researchers discovered that men who slept for less than 6 hours a night were 31 percent less likely to impregnate their partners than men who slept between 7 and 8 hours.

Those who slept 9 or more hours a night were 49 percent less likely to get their partners pregnant, too. (Here are 7 things you do every day that hurt your sperm.)

The study used pregnancy as the indicator of male fertility—not data on sperm counts or swimming ability— so it’s not clear yet how short or long sleep is actually messing with your sperm, says researcher Lauren Wise, Sc.D., professor of epidemiology at Boston University.

But it’s possible that sleeping too little can reduce your release of testosterone, a hormone vital for sperm production, she says. The reason long sleep hurts fertility is a little less clear, but it may be due to poorer sleep quality, which can also lower testosterone. (Here are 8 ways low testosterone affects your body.)

In fact, men in the study who reported trouble staying asleep throughout the night were 28 percent less likely to get their partner pregnant than those who had no problems.

It’s also possible that guys with low-quality sleep may also have other sperm-sapping habits, like smoking or drinking too much, or carry too much extra weight.

While researchers are still analyzing the data, Wise still recommends you shoot for 7 to 8 hours of solid sleep if you’re looking to become a father in the near future. (Avoid these 10 surprising things that are screwing up your sleep.)

Start working on your sleep habits about 3 months before you want to start trying to conceive: Sperm cells mature in around 72 days, so it might take just over 2 months to experience a fertility boost, she says.

This article originally appeared on MensHealth.com.