Gender preference is as old as conception itself, and so are theories about how to make it materialize-from ancient Talmudic advice to orient the marital bed north-south for a boy to Germanic folklore that suggests placing a wooden spoon under the bed ensures a girl. Even in this scientific age, theories-and couples eager to test them-abound.
Of them all, the Shettles method has the greatest following. Its premise is relatively simple: The Y-chromosome-carrying sperm (the one that results in a boy if it fertilizes an egg) is smaller, lighter, and faster-moving than sperm carrying the X (or female) chromosome. Conversely, the slower-swimming Xs are more resilient. According to Shettles advocate Pat Buie, author of Choose the Sex of Your Baby Naturally, this means that male sperm cells move through the woman's reproductive tract faster than female cells. In addition, an X sperm can withstand a more acidic environment, while a Y is more likely to survive in an alkaline environment. Accordingly, Buie counsels couples who prefer a boy to time intercourse to coincide with ovulation. This way, the swift Y sperm can beat the competition to the just-ripe egg (if the Y has to wait two days for an egg to be released, it will die). She also recommends rear-entry lovemaking (deeper penetration deposits the sperm closer to the cervix, thus avoiding the acidic vagina) and female orgasm, which increases cervical alkalinity. To conceive a girl, the Shettles method advises having sex no later than two days before ovulation (so that only the hardy X sperm will be alive when the egg ripens); using the missionary position (so that sperm penetrate less deeply and thus are exposed longer to the vagina's acidic secretions); and delaying female orgasm until after the man ejaculates.
Buie, a former nurse, maintains that the Shettles method has a 75 percent success rate overall and a 95 percent rate among her clients. There is little research, however, to back up her assertions. In fact, several fertility journals in the 1980s and '90s suggested that, if anything, girls are more likely when intercourse occurs at ovulation, and boys if it takes place before or after.
Enter J. Martin Young, M.D., author of How to Have a Boy and How to Have a Girl. The flaws in Dr. Shettles's theory, says the Texas pediatrician, stem from its being based on artificial insemination. For couples conceiving naturally, Dr. Young prescribes the opposite course.
Among his satisfied customers are Julie and Wolf Puckett. Five years ago, the Amarillo, Texas, couple consulted Dr. Young's book for help in conceiving a boy. Julie and Wolf charted Julie's temperature to determine ovulation, and they had intercourse several days before she was set to ovulate. Afterward, Julie raised her hips with a pillow, as Dr. Young advises. Whether by design or by chance, the system worked. The Pucketts' son, Hunter, is now 4.