This Da Vinci fetus is way past the critical window of exposure.

A relatively alarming study was published a couple of years ago that suggested that a pregnant woman’s behavior can determine the fertility of her unborn son. Sperm quality from 387 men was compared to beef consumption their mothers reported while pregnant with them. They found that the sons of “high beef consumers” (>7 beef meals/week) had sperm counts that were 24% lower than in men whose mothers ate less beef. Interestingly, sperm counts in the sons were not related to mother’s consumption of other meat or to the son’s consumption of meat. In essence, the author’s thought that estrogens in beef consumed by women may alter the testis development of their unborn sons and may adversely affect the son’s fertility. Similarly impressive decreases in semen quality have been described in the sons of women who smoked during pregnancy.

Sounds almost biblical, doesn’t it? I bring this up because of a point that I made in last week’s blog. In “The Curse of Women’s Urine,” I mentioned how xenoestrogens or environmental estrogens have been shown in animals to act at a very precise point in the developing male fetus and result in intersex conditions at birth or infertility as adults. Well, as the study of mothers’ beef intake reveals, the same issues may also exist in humans. As Aristotle once said: “At his best, man is the noblest of all animals; separated from law and justice he is the worst.”

Time for a quick lesson in biology. When do testicles develop in humans? Believe it or not, when male fetus in just 4 weeks old, the location where the future testis will be is organized (the urogenital ridge). Two weeks later, the primitive germ cells (sperm precursor cells) migrate to the urogenital ridge and set up what is to later become the testis. About 1-2 weeks after that, “sex cords” develop in the primitive testis, setting up the architecture of the mature organ. So, by 8-12 weeks of pregnancy, the human testis is virtually a complete organ, holding within it all of the potential it will ever have.

So the “critical window” of exposure for the human testis, that period in which even a potentially small exposure could wreak significant developmental and long lasting havoc, is about the time when women actually just realize that they are pregnant. The time of morning sickness and painful breasts.

So, does male infertility begin in the womb? Still not clear, really, as all studies have flaws. For example, in the study of beef eating pregnant women, the cohort of son’s whose sperm counts were so thoroughly examined were ALL fertile. That’s right, their wives were all pregnant. Oscar Wilde couldn’t have said it better when he said: “The pure and simple truth is rarely pure and never simple.”