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Teens More Likely to Become Pregnant in March than Any Other Month of the Year

Tim Boyer's picture

A 5-year study of monthly conception rates shows that the month of March is the peak season for teenage pregnancy. So much so, that in a relative comparison to adult pregnancy rates, teens outperform their elders. Researchers hypothesize that although there may be more-scientific explanations related to the biology of seasonal fertility, they concede that Spring Break may be a likely cause.

March is teen pregnancy season

The affect seasonal fluctuations have on reproduction within the animal kingdom are well understood with many species. Conditions of temperature, light, rainfall, drought and food availability can directly affect when and how often a species reproduces during a particular year.
Birds are an interesting example because as harbingers of spring and new found love, poets have waxed with immortal lines such as, “In the spring a livelier iris changes on the burnished dove; In the spring a young man’s fancy lightly turns to thoughts of love.”

Nowhere do those lines ring more true than with many species of male birds in preparation of finding a mate and looking for that first, sweet, tender cloacal kiss in the bushes.

Before the cloacal kiss occurs, however, the male must undergo some rather dramatic changes. As temperatures begin to warm and the days begin to lengthen, rays of light stimulate photoreceptors on the male’s brain. This in turn leads to hormone release that initiates enlargement of the testes. In some species of bird, the testes grow 300-fold and may comprise 10% of the male’s total body weight. Behavior is affected too. Cardinals attacking their reflections in windows and mockingbirds singing throughout the night are common signs of spring due to an enlarged testis.

The females likewise undergo some changes: reproductive organs enlarge, eggs develop in the ovaries, brood patch formation begins and nesting behaviors manifest.

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During copulation, the male mounts the female, tail feathers part, and swollen lips of both sexes’ cloacas (a combination excretory and reproductive sinus) touch momentarily in what is referred to as a “cloacal kiss” as sperm is transferred from the male to the female. Sperm may lie in storage at the lower end of the female oviduct for a period before eventually swimming toward the upper end to fertilize a clutch of eggs.

Goshawks are known to copulate as often as 500-600 times per clutch of eggs, whereas the Eurasian Skylark seems to think that once is enough. Biologists believe that multiple copulations prevents competing males from cuckolding the first male in an attempt to pass their genes in a willing female by diluting his stored semen with theirs.

But I digress.

In the teen pregnancy study, researchers from the Department of Obstetrics and Gynecology, Queen's University, Kingston, Ontario charted 838 adolescent pregnancies over a 5-year period. They compared the adolescent pregnancies to a similar sample of randomly selected adult pregnancies over the same 5-year period. What the researchers found was a statistically significant monthly trend in adolescent pregnancies compared to adult pregnancies. Their results showed that during the month of March, adolescents had a pregnancy rate of 10.5% compared to the 7.3% in adults.

A scientifically accurate explanation for this peak in March is not immediately apparent from the study’s data; however, according to co-author Mary Anne Jameson, an Associate Professor in Queen's Departments of Obstetrics & Gynecology and Pediatrics, “This adolescent pregnancy peak may be explained by biological reasons such as variations in fertility over the course of a calendar year, but it's also possible that this increased conception rate in March is because of Spring Break."

With those two possibilities in mind, maybe a comparison to birds is not such a feather-brained digression after all.
One final point of interest is that the study also showed that during the month of December, adults had their own reproduction peak of 10.4% compared to 8.5% with adolescents. Perhaps Christmas has (ahem) something to do with this as well.

Source: Kaitlyn Turnbull, Laura N. Nguyen, Mary Anne Jamieson, Stephanie Palerme. Seasonal Trends in Adolescent Pregnancy Conception Rates. Journal of Pediatric and Adolescent Gynecology, 2011; 24 (5): 291 DOI: 10.1016/j.jpag.2011.04.005