You already know that exposure to light at night can screw with your body’s internal clock—keeping you from scoring quality sleep and even screwing with your weight loss efforts. Now, researchers say it appears to throw off something else: your fertility. In a new review of previous studies published in the journal Fertility and Sterility, a research team concluded that steady artificial nighttime light or even periods of light disruption when you're trying to sleep can warp your internal clock, make it harder to conceive or even affect fetal development if you’re already pregnant.

It all has to do with the hormone melatonin, which the brain normally cranks out in response to darkness. Melatonin has been dubbed the "sleep hormone" because it helps us doze off and get the snooze time your body needs. But melatonin is also produced in the reproductive tract and has a protective effect on eggs, blocking damage from free radicals—especially during ovulation, when eggs are most vulnerable, write the researchers. The suppression of melatonin production during pregnancy can harm a fetus too, they add, potentially triggering problems with a developing baby's biological clock and contribute to health issues down the line.

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The more light you're exposed to at night, when your body is trying to wind down to get you to sleep, the more melatonin production is decreased—reducing the odds of conception or threatening fetal health, researchers concluded.

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Bottom line: If you're hoping to conceive, or you're already expecting, make sure your body is pumping out optimal levels of melatonin by maintaining a stable light-dark environment, the researchers suggest. Translation: Avoid light disturbances close to bedtime or while you are trying to score shuteye. Keep the tablets and phones out of your bed, shut off the TV and other light-emitting screens, and make sure illumination from streetlamps isn't creeping in through your bedroom windows.

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