“Seasonal Trends in Adolescent Pregnancy Conception Rates”
Journal of Pediatric and Adolescent Gynecology Volume 24, Issue 5, October 2011, Pages 291-29
Kaitlyn Turnbull, et al., reported the following:
There was a significantly different monthly trend seen in adolescent pregnancy conceptions when compared with the adult group (?2 = 24.38, df = 11, P = 0.0112). The adolescent group was observed to have a unique peak in the number of pregnancies conceived in March (10.5% of pregnancies conceived compared to 7.3% in adults). In addition, 8.5% of conceptions in adolescents occurred in December compared to 10.4% in adults.
There are several plausible explanations for the modest but real differences identified in this study including trends in fecundity/fertility or social/school events that lead to increased sexual activity. Peaks in conception indicate times when a greater need for health care services exists, and when preventive education can be most effective."
I wish to suggest an hypothesis which may explain these results. Copyright 2012, James Michael Howard, Fayetteville, Arkansas, U.S.A.
Testosterone in men and women is highest in the fall and winter and lowest in spring and summer. It is the testosterone in women that is important to explaining these findings, that is, in relation to dehydroepiandrosterone (DHEA): the testosterone to DHEA ratio.
Testosterone antagonizes the availability of DHEA, that is, testosterone reduces available DHEA. When testosterone is high, so is DHEAS, the precursor of DHEA. If DHEAS is high, DHEA may not be readily available. A strong case may be made for the positive effects of sufficient DHEA for conception.
As we enter fall and winter, testosterone increases which reduces DHEA. As we enter spring, the ratio of DHEA to testosterone increases because testosterone reduces its negative effect on availability of DHEA. Therefore, the likelihood of conception is increased in spring because DHEA increases. This will increase conceptions in spring. Additionally, since testosterone is higher in adolescence compared to adulthood, the adolescent testosterone to DHEA ratio is increased compared to that of adults. Therefore, adults will exhibit more conceptions in winter compared to adolescents. Conversely, conceptions will be higher in adolescence because of increased DHEA.
Evolutionarily this may be very beneficial in humans. DHEA reduces fat deposition. High testosterone in fall and winter would reduce the anti-obesity effect of DHEA, that is, lowering DHEA in winter would increase fat deposition which would be beneficial to conceptions in the spring. ("Androgens in Human Evolution," Rivista di Biologia / Biology Forum 2001; 94: 345-362. If your library does not subscribe to "Rivista... ," you may read this at: http://anthropogeny.com/Androgens%20in%20Human%20Evolution.htm ) It is part of my work that testosterone is increasing within our populations, so obesity and related morbidity is also increasing as the testosterone to DHEA ratio increases.
Another application of the foregoing hypothesis may explain the finding (2007) that season of conception affects school performance.
“When researchers linked standardized test scores of 1,667,391 Indiana students in grades 3 through 10 with the month in which each student had been conceived, they found that children conceived May through August scored significantly lower on math and language tests than children conceived during other months of the year.” (Reuters)
If a mother is high in testosterone and the influence of testosterone affects her fetus for longer periods, this would adversely affect the availability of DHEA in the fetus. This may result in less growth and development of the fetal brain which would translate into diminished abilities of the advanced frontal lobes. The researchers who reported the findings, above, suggested the cause is pesticides and herbicides in the environment.
This may also act to explain some other findings regarding negative pregnancy outcomes. For example, seasonality and place of birth have been tied to the incidence of schizophrenia. “Although a history of schizophrenia in a parent or sibling is associated with the highest relative risk of having the disease, the place and season of birth account for many more cases on a population basis.” (The New England Journal of Medicine 1999; 340: 603-608; Mortensen, et al.)
Mortensen, et al., found “the risk of schizophrenia was associated with the degree of urbanization of the place of birth…” A report comparing rural areas and a large city found that testosterone is higher in the large city (Folia Histochem Cytobiol. 2001;39 Suppl 2:38-9). They also reported that “The risk was also significantly associated with the season of birth; it was highest for births in February and March and lowest for births in August and September.” This relates to time of exposure to maternal testosterone. The probability of schizophrenic offspring is increased in young or old mothers. Young mothers would increase the negative effects of maternal testosterone while old mothers would increase the negative effects of low DHEA, which is characteristic of aging.
The “testosterone to DHEA ratio” is important in our individual lives and our species.