Indeed, an ultrasound examination can determine the sex of the fetus by 20 weeks of intrauterine life. In fact, with the latest equipment, the diagnosis can be made as early as 11 weeks, but is this kind of ultrasound examination safe?

Apparently yes. Evidence indicates that ultrasound, as it is currently used for medical diagnostic purposes, is harmless.

Actually, although ultrasonography is the most widely used — and perhaps the cheapest — method for determining fetal sex, there are other procedures which are as equally reliable such as amniotic fluid culture, chorionic villus sampling and serumDNA QPCR technique.

Now, on your first question, are there things parents can do to pre-select the sex of their next baby? If you are looking for do-it-yourself measures, the answer is none.

There are articles that occasionally get printed in popular magazines and newspapers that describe certain measures couples can take to ensure that their next baby is of their desired gender.

Some enterprising people have likewise been marketing kits — many through the Internet – that allow couples to greatly influence the gender of their next child.

In essence, according to the authors of these articles and sellers of kits, the sex of a baby depends on several factors, namely: The diet of both mother and father, vaginal pH (acidity or alkalinity) at the time of sexual intercourse, timing of the intercourse relative to ovulation, frequency of sexual intercourse and position of the partners during the sex act, or more specifically when the husband ejaculates.

Thus, a couple desirous of male offspring (like you) should observe a period of abstinence (several days) from sex and then engage in sex at about the time of ovulation, but before the sex act, the woman should douche with baking soda to increase her vaginal pH, etc.

Scientific evidence, however, have shown that these techniques do not alter the sex ratio at birth at all.

Some years back, I was given a Chinese calendar by a reader of this column which, if followed by a couple, will supposedly guarantee a baby boy. But I immediately dismissed the calendar as worthless. After all, Chinese culture places a premium on male offsprings and if that calendar works at all, then, the sex ratio in China should be overwhelmingly in favor of boys by now, which is not the case.

So, there are no do-it-yourself ways to pre-select the gender of your next child, but there are methods that can. Unfortunately these methods are not ethically acceptable in the Philippines. Also, they are very expensive. In the US, they cost ,000 upwards.

At any rate, just for your information, the most reliable of these sex pre-selection methods involves obtaining sperms from the husband and sorting the sperms into those that contain the X-chromosomes sperms (that give rise to females) and those that contain the Y-chromosome (that give rise to males) by a procedure called flow cytometry.

Then an ovum is surgically obtained from the mother’s ovary and fertilized in vitro (test tube fertilization) with the chosen sperms. The fertilized ovum is then implanted into the mother’s (womb) where it is allowed to grow to maturity.

The procedure described above can pre-select the sex of a baby, but its more acceptable application is the prevention of X-linked genetic diseases. X-linked diseases occur in about one in 1,000 live births.

These diseases, which include hemophilia (characterized by spontaneous bleeding), Duchenne muscular dystrophy, and X-linked mental retardation, usually arise in the male offspring of carrier mothers. Thus, carrier mothers who want to have a child who is free from disease can do so by pre-selecting the sex of their baby so that they give birth to a girl instead of a boy.