Sunlight may affect fetal brain development through its effects on maternal melatonin production as well. Melatonin is produced by the pineal gland, a pea-size organ deep in the brain; its synthesis is suppressed by sunlight. Recent research suggests that beyond helping to regulate the sleep-wake cycle, melatonin may act as an antidepressant. Variations in a mother's melatonin levels could directly affect the brain of the fetus and, in turn, his or her emotional development.
Amateur astrologers will notice similarities between the mental health issues associated with different birth seasons and personality traits traditionally ascribed to the sun signs: an increased risk of schizophrenia in think-outside-the-box Aquarius and visionary Pisces, and of anorexia with food-fixated Taurus.
As season-of-birth effects are studied, Pisces, Virgos, and (gasp) Scorpios shouldn't worry. Like your genes, your sign doesn't automatically mean you're condemned to a lifetime of horror-scopes.