The amount of sleep women undergoing in vitro fertilization get each day may have an impact on their pregnancy outcomes, according to a new study.

And too much might be just as harmful as too little.

A team of researchers from Korea analyzed the self-reported sleep habits of more than 650 women before undergoing IVF and broke them into three groups: “Short sleepers” got four to six hours per day; “moderate sleepers” got seven to eight; and “long sleepers” got nine to 11. Overall, pregnancy rates were higher in the moderate sleepers than in women who clocked more than nine hours a night — 53 percent versus 43 percent respectively. The pregnancy rate among short sleepers was roughly 46 percent.

“We don’t know a lot about sleep and fertility — there’s not very much research out there,” said Dr. Carmelo Sgarlata, a reproductive endocrinologist with the Reproductive Science Center of the San Francisco Bay Area. Sgarlata, who did not work on the study, called the findings “new and interesting,” but cautioned that they were preliminary and do not establish clear cause and effect.

Getting enough sleep benefits reproductive hormone secretion, according to the study’s authors, who presented their findings at the American Society for Reproductive Medicine’s annual meeting in Boston this week. But while that could be helpful for overall fertility, as well as IVF outcomes, too much sleep may disrupt circadian rhythms — the internal biological clocks that govern sleep cycles — as well as certain hormone cycles, thus impairing fertility.

“We know that sleep habits can certainly alter circadian rhythms, hormone secretions and menstrual cycles,” echoed Dr. Evan Rosenbluth, a reproductive endocrinologist who also works with the Reproductive Science center, in an email to The Huffington Post. “[But] the effect on infertility is a little harder to tease out, because there are so many details that are hard to control for. For instance, sleep quality and other patient variables, such as stress and weight, which have known effects on fertility can also have effects on sleep. So it becomes a chicken and egg dilemma.” Rosenbluth is not affiliated with the study.

Sgarlata explained that there are many factors with a much clearer impact on fertility that have nothing to do with sleep or modifiable behaviors. “Often, people who get a lot of sleep have depression, or they may have seasonal affective disorder, all of which could certainly affect fertility.”

Yet the new research joins a growing body of studies investigating the connection between sleep and fertility. A review presented last summer at the European Society of Human Reproduction and Embryology’s annual meeting in London found that shift work was clearly tied to miscarriage, menstrual problems and failure to become pregnant after one year of trying to conceive.

And while researchers do not fully understand how sleep affects fertility and pregnancy, or to what degree, the new study argues that moderate sleep should be recommended to patients undergoing IVF cycles in order to improve their outcomes.

Sglarata took it one step further. “I would say that a good, useful seven to eight hours of sleep a day should be recommended for any patient attempting to get pregnant,” he said.
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