Similar photoperiod-related birth seasonalities among professional baseball players and lesbian women with an opposite seasonality among gay men: Maternal melatonin may affect fetal sexual dimorphism.

Based on pre-mid-20th-century data, the same photoperiod-related birth seasonality previously observed in schizophrenia was also recently found in neural-tube defects and in extreme left-handedness among professional baseball players. This led to a hypothesis implicating maternal melatonin and other mediators of sunlight actions capable of affecting 4th-embryonic-week developments including neural-tube closure and left-right differentiation of the brain. Here, new studies of baseball players suggest that the same sunlight actions could also affect testosterone-dependent male-female differentiation in the 4-month-old fetus.

Conception season and cerebral asymmetries among American baseball players: implications for the seasonal birth effect in schizophrenia.

People with schizophrenia and children born with neural tube defects both tend to be conceived most often in May-June, about a month before the summer solstice, and least often in November-December, a month before the winter solstice. Such timings, coupled with evidence of cerebral asymmetry deficits in schizophrenia, and evidence that asymmetry development and neural tube closure represent concurrent fourth-embryonic-week processes both sensitive to oxidant stress, led us to the hypothesis that pro-oxidant sunlight actions capable of affecting the mother's blood could result in a peri-June peak of inhibition and a peri-December peak of facilitation of both processes. Here, using birth and hand preference data from baseball statistics, we tested the hypothesis's prediction that, as a group representing minimal cerebral lateralization, left-handed players would show the same conception rhythm as that observed in the above disorders.

Similar rhythms of seasonal conceptions in neural tube defects and schizophrenia: a hypothesis of oxidant stress and the photoperiod.

Background: Numerous studies have found that people with schizophrenia tend to be born most often in late winter and least often in late summer. The same rhythm appears in the birth of children with neural tube defects (NTDs). In the northern hemisphere, both disorders thus show a conception peak in May-June and a trough around November-December.