The Whelan Method of Sex Selection

By: Alysse Blight

The Whelan Method of Sex Selection

The Whelan Method of sex selection is a method for increasing a couple’s probability of conceiving an infant of the desired sex through timing intercourse. Elizabeth Whelan, a public health researcher, suggested that couples only have intercourse at specific times during the woman’s menstrual cycle based on whether they wanted a female or male infant. Whelan published her method in her book, Boy or Girl, in 1977. During the mid-to-late twentieth century, researchers offered other methods of timing intercourse for sex selection, but their results were based on studies of artificial insemination, rather than naturally occurring pregnancies. Whelan claimed her method was supported by natural insemination studies and that it worked for couples trying to conceive an infant of a particular sex.

During her doctoral studies at the Harvard School of Public Health in Cambridge, Massachusetts, Whelan completed a historical analysis of the development of methods for sex selection that involved intercourse timing. In 1974, she published a review paper, “Human Sex Ratio as a Function of the Timing of Insemination within the Menstrual Cycle,” in the journal Social Biology. In that paper, she presented an analysis of sex selection hypotheses, or theories about what factors determine whether a fetus develops male or female. Whelan’s work reviewed research from ancient times to the late twentieth century. Throughout the paper, she identified many studies that supported a relationship between the timing of intercourse and the sex of the infant. According to Whelan, the studies could not be compared or tested against each other because of the differences in methods.

In that same paper, she described the work of Rodrigo Guerrero, a fellow doctoral student at Harvard. Guerrero studied the relationship between the timing of intercourse, an infant’s sex, and the use of natural intercourse or artificial insemination. Artificial insemination is the process of using a syringe to inject sperm directly into a female’s uterus for fertilization. Guerrero asserted that artificial insemination occurring early in the woman’s the menstrual cycle, specifically three or more days before ovulation, increased the probability of female infants. Guerrero also asserted that natural intercourse occurring early in the woman’s menstrual cycle resulted in male infants more often.

Ovulation is the stage of the menstrual cycle when a woman’s egg is released from her ovaries. The female body goes through physical and chemical changes around the time the egg released. Those changes are usually accompanied by change in body temperature. An increase in body temperature is associated with the presence of progesterone in the bloodstream. Progesterone is only present in the bloodstream after ovulation has occurred, and therefore a spike in body temperature indicates that an egg has already been released. According to Guerrero, detecting a woman’s temperature increase is the most accurate way of determining the day of ovulation.

After working with Guerrero, Whelan developed specific methods for couples to follow in order to increase their chances of producing an infant of the desired sex. In 1977, Whelan compiled the results of her and Guerrero's research and provided her method for sex selection in a book titled Boy or Girl. According to Whelan’s method, couples should have intercourse two or three days prior to ovulation to increase their chances of conceiving a female infant. To increase the probability of conceiving a male infant, couples should have intercourse between four and six days before ovulation. According to Whelan’s research, the method increases the probability of conceiving a male by eighty-six percent and increases the probability of conceiving a female by sixty-six percent. According to Whelan, without her methods, the probability of conceiving either sex is fifty percent. Those percentages are based on seven clinical research trials about the timing of natural conception and sex outcomes. One of those studies followed the timing of intercourse, conception, and birth of 3,658 infants.

In her book, Whelan offered suggestions about how to detect ovulation so couples could time their intercourse precisely. She suggested that women track their body temperature by using an oral thermometer every morning before getting out of bed. According to Whelan, women should begin tracking on the first day of their twenty-eight day menstrual cycle. Whelan also suggested that women track their temperature for a few menstrual cycles to identify the average day of the temperature spike. In her book, Whelan wrote that women should consider the day before the temperature spike as the day of ovulation. Then, during their next cycle, women should have intercourse on the day before the temperature spike.

The Whelan method was different from another popular sex selection timing method, called the Shettles Method. The Shettles Method was developed seven years prior to the publication of Whelan’s book. In 1970, physician and researcher Landrum B. Shettles suggested that couples have intercourse on the day of ovulation or shortly after in order to produce a male offspring. Shettles explains his methods in a book titled Your Baby’s Sex, Now You Can Chose. As of 2006, Shettles’ book had six revised editions and sold over one million copies. However, as part of her research, Whelan found that Shettles presented his method for use with natural conception, even though he based his method on studies about artificial insemination. Whelan cited several studies in her book that demonstrated Shettles’ method did not work. In those studies, 74 out of 131 infants born to couples who used Shettles’ method were not the desired sex. Despite Whelan’s findings, Shettles’ method is still one of the most well-known methods of sex selection by intercourse timing.

Since the publication of Whelan’s book, many researchers have refuted her theories regarding the relationship between intercourse timing and an infant’s sex. A study published in The New England Journal of Medicine in 1995 refuted all claims that intercourse timing affects the outcome of an infant’s sex. That study asserted that there was no association between intercourse timing and sex outcome, and that timing of intercourse holds no value in sex selection.


  1. Guerrero, Rodrigo. “Type and Time of Insemination within the Menstrual Cycle and the Human Sex Ratio at Birth.” Studies in Family Planning 6 (1975): 367–71.
  2. James, William. “The Human Sex Ratio. Part 1: Review of the Literature.” Human Biology 59 (1987): 721–52.
  3. Rorvik, David Michael and Landrum B. Shettles. Your Baby’s Sex: Now You Can Choose. New York City: Bantam Books, 1971.
  4. Rorvik, David Michael and Landrum B. Shettles. How to Choose the Sex of Your Baby: The Method Best Supported by Scientific Evidence. New York City: Broadway Books, 2006.
  5. Wilcox, Allen J. “Timing of Intercourse in Relation to Ovulation – Effects on the Probability of Conception, Survival of the Pregnancy, and Sex of the Baby.” The New England Journal of Medicine 333 (1995): 1517–21.
  6. Whelan, Elizabeth. Boy or Girl. New York City: Pocket Books, 1977.
  7. Whelan, Elizabeth. Boy or Girl. New York City: Pocket Books, 1984.
  8. Whelan, Elizabeth. “Human Sex Ratio as a Function of the Timing of Insemination within the Menstrual Cycle.” Social Biology 21 (1974): 379–84.


How to cite

Blight, Alysse, "The Whelan Method of Sex Selection". Embryo Project Encyclopedia ( ). ISSN: 1940-5030


Arizona State University. School of Life Sciences. Center for Biology and Society. Embryo Project Encyclopedia.

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