MANILA -- If you're hoping to conceive a girl or a boy, you need to understand the nature of the of the egg and the sperm cell, and find out how nature chooses boy or girl.

In DZMM's "Private Nights", Dr. Lulu Marquez explained the most used method on determining the sex of an offspring: the Shettles Method.

Dr. Landrum B. Shettles published a groundbreaking report, "How to Choose the Sex of Your Baby," discussing the different characteristics sperm.

"It is the sperm that fertilizes the egg that will determine the sex of your baby," Dr. Marquez said, noting that some sperm cells carry the X-chromosome, while others carry the Y-chromosome.

"If an X-chromosome-carrying sperm fertilizes the egg, the baby will be a girl. If a Y-chromosome-carrying sperm fertilizes the egg, the baby will be a boy."

The boy sperm is said to be faster and smaller and has shorter life than the girl sperm. Its life is also shorter than the girl sperm.

The girl sperm, meanwhile, is slower than the boy sperm but is able to withstand the acidic cervical environment before fertile cervical fluid is produced.

There are three premises, according to the Shettles Method:

1. Timing

"Importante ang menstrual cycle ng babae ay regular," Dr. Marquez advised. "You can time intercourse. Women are fertile on the second nine days of menstruation. The life of an egg, however, is only for 24 hours."

To get a boy: Marquez suggested to time intercourse as close to ovulation as possible. "Choose the middle day of the second nine days of menstruation."

To get a girl: Because the girl sperm has a longer life than the boy sperm, it is better to have sex two to three days before the ovulation.

2. Sexual position

"Choose a sexual position that favors conception of your preferred sex," the doctor said.

To get a boy: Marquez said to do the "doggy style." "Kung mas closer ang ejaculation sa cervix, then chances are mas mabilis na makakarating ang boy sperm sa egg," Dr. Marquez said.

To get a girl: Avoid deep vaginal penetration. Dr. Marquez recommended "missionary position" or any position that will hold the sperm slightly away from the cervix.

3. True or fake orgasm

Women have an orgasm to increases the alkaline secretions in the vagina.

To get a boy: Boy sperm cannot survive if the vagina is acidic. Dr. Marquez recommended that women should have an orgasm before or at the same time as their male partner.

To get a girl: Women should avoid orgasm because alkaline is disadvantageous to the girl sperm.

The doctor warned, however, that the Shettles Method is not guaranteed to work. Some people report success while others have not gotten their chosen sex. It is still the best to consult a physician about the most reliable methods on having a boy or girl.