DETERMINING GENDER OF BABY (BOY OR GIRL)
The miraculous process of human reproduction is very wonderful and surrounded
in mystery also myth. There are a lot of theories about how to improve fertility,
carry out the morning sickness and include labor. To predicting a baby's gender
is another way to knowing as opinions based largely in folklore and intuition.
I have recently heard it suggested that sperm for male children come from one
testicle, and sperm for female children come from the other one. The evidence
for this concept? A man who had damage to one testicle (from mumps) had five
sons because his "female testicle" was not working. This myth follows
a basic misunderstanding about gender determination (not to mention that when
mumps causes inflammation of the testicle, it usually affects them both).
How is Baby Gender Determination Works
Although there is no such thing as a "female testicle" or a "male
testicle," a baby's gender is determined by his or her father. If the father
provides an X chromosome, the baby will be female, and if he supplies a Y chromosome,
the baby will be male. The body has no mechanism to segregate the X sperm from
the Y sperm.
Because sperm containing X chromosomes and sperm containing Y chromosomes are
nearly equal in number and because the chances for either type of sperm to fertilize
an egg are roughly equal, each naturally occurring conception leads to an equal
chance of having a boy or a girl.
Mothers can provide only an X chromosome, so they do not have the same influence
over gender.
Understanding the Myth of Baby Gender
Myths regarding how baby boys or girls are determined probably have their roots
in at least two faulty assumptions. One is the concept that past events alter
future ones. For example, the chances that a couple will have five boys in a
row is 1 in 32 (or about 3 in 100); but with each individual child, the chances
of having a boy are 1 in 2 (50%), even if the couple already has four sons.
Another assumption is that when something unusual happens (for example, having
five boys in row), there must be an explanation that is separate from the normal
state of affairs. Although unusual things do happen, they do not imply that
the laws of nature should be repealed!
It is perhaps easy to see how the notion of "testicular gender" might
take hold, since there are two genders and two testicles. For a father who has
five sons, it may be tempting to assume that a single functioning testicle has
led to this otherwise unlikely situation, yet men who have had a testicle removed
surgically (for example, because of an injury or a tumor) still, on average,
father male and female babies in equal proportions.
Changing Your Odds
Despite what you may have heard, there is relatively little a couple can do
— through naturally occurring conception — to alter the chances
of conceiving a boy or a girl. Many people believe that position during intercourse,
diet, the lunar cycle or gender patterns in the couple's families all contribute
to the sex of the baby. In fact, these factors have no well-established effect.
However, the timing of intercourse can have an effect. Sperm carrying Y chromosomes
apparently swim faster but do not survive as long as their X-carrying counterparts.
So if a couple has intercourse right at the time of ovulation, the faster-swimming
male sperm have an advantage, and a male baby is slightly more likely —
but only very slightly. But if the timing is a day or two earlier, more of the
male sperm die out, and a female baby is a bit more likely.
Even so, it is often difficult to time ovulation accurately, and your odds
of determining gender do not change much. Without the application of advanced
(and sometimes invasive and expensive) technology, such as in vitro fertilization,
the chances of conceiving a boy or a girl remain close to equal.
The Bottom Line
If you have a strong preference for a boy or a girl, your options are limited.
You could plan to have enough babies so both genders are eventually represented.
Or it may be better to rethink your position and hope for a healthy baby of
either sex.
(by Robert H. Shmerling, M.D., is associate physician at Beth Israel Deaconess
Medical Center and associate professor at Harvard Medical School.)
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