We've come right back to the "biological clock." Research shows that women who are pregnant or hoping to conceive should listen to their circadian rhythms and avoid artificial light at night. Sleep doesn't just help the body rejuvenate and promote growth in kids; it also protects a woman's eggs from stress. That's because melatonin is believed to have antioxidant qualities and defends the body against inflammation while stimulating the immune system, particularly during ovulation [sources: Klein, Nierenberg].
When the lights go on at night, melatonin production slows or stops. Experts say that women who are expecting should maintain steady sleep patterns that conform with the light and dark cycles going on outside. That means eight hours of darkness with little or no interruptions each night. The dark, not actual sleep, is the key. The body produces melatonin as a reaction to darkness and will continue doing so, even if you can't sleep. Among other effects, researchers have found that disruptions in this routine can lead to attention-deficit/hyperactivity disorder and autism-related disorders in young children [sources: Klein, Nierenberg].