Stay Up Late? How It Could Hurt Your Fertility

A pregnant woman lays in bed.
(Image credit: Monkey Business Images/

Women who want to become pregnant or are expecting a baby should avoid light during the night, a new report suggests.

Darkness is important for optimum reproductive health in women, and for protecting the developing fetus, said study researcher Russel J. Reiter, a professor of cellular biology at the University of Texas Health Science Center in San Antonio.

In a review of studies published online July 1 in the journal Fertility and Sterility, Reiter and his colleagues evaluated previously published research, and summarized the role of melatonin levels and circadian rhythms on successful reproduction in females.

The evidence shows that "Every time you turn on the light at night, this turns down the production of melatonin," Reiter said. [7 Ways Pregnant Women Affect Their Babies]

Melatonin, a hormone secreted by the pineal gland in the brain in response to darkness, is important when women are trying to conceive, because it protects their eggs from oxidative stress, Reiter said. Melatonin has strong antioxidant properties that shield the egg from free-radical damage, especially when women ovulate, the findings reveal.

"If women are trying to get pregnant, maintain at least eight hours of a dark period at night," he advised. "The light-dark cycle should be regular from one day to the next; otherwise, a woman's biological clock is confused."

Light pollution

Eight hours of darkness every night is also optimal during pregnancy, and ideally, there should be no interruption of nighttime darkness with light, especially during the last trimester of a pregnancy, Reiter said.

Turning on the light at night suppresses melatonin production in women, and means the fetal brain may not get the proper amount of melatonin to regulate the function of its biological clock, he said.

Animal studies have suggested that disturbances in the mother's light and dark environments may be linked with behavioral problems in newborns. This has led some researchers to speculate that similar disruptions of the light and dark cycles when a woman is pregnant may be related to the rise in attention-deficit/hyperactivity disorder (ADHD) or autism spectrum disorders in young children.

"We have evolved for 4 million years with a regular light-dark cycle that regulates circadian rhythms," Reiter said. "We have corrupted this with the development of artificial light, which disrupts the biological clock at night and suppresses levels of melatonin."

"There is a biological price to pay for disturbing the light," Reiter said.

What women can do

So what should women who want to have a baby or are already pregnant do to avoid disruptions to the light-dark cycle?

Darkness is necessary for a regular biological clock and to produce a good dose of melatonin, Reiter said. However, he noted, "staying in darkness has nothing to do with sleep." Sleep is nice, Reiter said, but it's the darkness that's needed for the brain to produce melatonin.

He recommended making sure the bedroom is dark, with no outside light coming in through the windows, or from a television or gadget's glare. Those who want a night-light should choose a red or yellow light, rather than a white or blue light, which can disrupt circadian rhythms. And those who can't sleep should avoid turning on the light.

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Live Science Contributor

Cari Nierenberg has been writing about health and wellness topics for online news outlets and print publications for more than two decades. Her work has been published by Live Science, The Washington Post, WebMD, Scientific American, among others. She has a Bachelor of Science degree in nutrition from Cornell University and a Master of Science degree in Nutrition and Communication from Boston University.