Further, acidic environments harm Y sperm, according to the theory, making conception of a girl more likely[1] The Shettles method aims to exploit these two factors.
To have a boy, insemination should occur as close as possible to the moment of ovulation so that the faster, Y-sperm arrive first and achieve conception, according to the hypothesis.
The book has proven sound through the past 27 years; and, like the house in the scriptures, built on the rock rather than the sand.” There is some disagreement among researchers as to how and whether the method works.
[2] In contrast, another study from the New England Journal of Medicine (1979) found that "[our] results ... demonstrate that insemination on different days of the menstrual cycle does lead to variations in sex ratio.
"[3] While this second study was larger, it did not track the levels of LH in the blood but instead used cycle lengths to determine probable time of ovulation.
Another study, reported upon in Discover Magazine in 1988 called "Girls from Space," found that both high altitude tactical pilots and astronauts fathered far more daughters than sons.