How to Know Baby's Sex - It's A Boy Or Girl?

Since the world is world, curiosity about the baby's sex is almost universal among prospective parents. Once the couple discovers that the woman is pregnant, the first question that invariably comes to mind is: will be a boy or girl?


In this article we will talk about the most effective ways to detect the sex of the fetus, including ultrasound examinations and blood tests. We will also talk about the myths and the existence of scientific evidence behind popular beliefs, such as tables, calendars or sympathies.


Unlike our grandparents, who had to wait until the day of birth to discover the sex of the baby, thanks to technological advances, we can already identify the gender of the fetus as early as 8 weeks of pregnancy.

There are several ways to find out the baby's sex during pregnancy with ultrasound and fetal sexing through the mother's blood currently the most popular forms. Let's talk briefly about some methods of fetal sex determination currently available.

a) Ultrasound to identify the sex of the baby

In recent decades, fetal ultrasound has become the most common way to identify the gender of the fetus. Ultrasound is a great test because it is simple, cheap, painless and without risk to mother or fetus. In fact, determining the baby's gender is just one of dozens of obstetrical ultrasound utilities. In general, no one does ultrasound only to whether it is a boy or girl. The sonographic evaluation is part of routine prenatal care and the sex determination of the fetus ends up being included along with other assessments of gestational health status.

Sex determination is made very simply: see if the baby has a penis or a vulva between her legs. Saying so may seem easy, but despite the differentiation of the genitalia begin around the 6th week of pregnancy before 14 weeks is very hard to tell through the image of the ultrasound if the baby is a male or female sexual organ.

The position of the baby in the womb is essential so that the doctor can have clear pictures. The baby may have already genitalia fully formed, but if his position is not favorable, the doctor can not get a proper angle to evaluate the pelvic region. When the baby is a boy, is often easier, and even at 12 weeks can now be possible to determine the gender of the fetus. But when the doctor can not see the penis, this can mean a girl or just an improper angle for viewing the body.

From the 18 th and 20 th, the genitalia is usually well-formed and ultrasound accuracy rate is over 90%. But even in this gestational age can be no doubt, especially if the baby's position is not the most appropriate. When this is so, determining the sex ends up at a later ultrasound, with already more advanced pregnancy.

Despite the high hit rate, ultrasound can go wrong, it is a test that depends on human interpretation. The error can be for both sexes, but most mistakes occur with boys who are wrongly identified as girls by the ultrasound image.

b) Fetal Sexing

The fetal sexing is a test that has gained great popularity in recent years. It is made through the mother's blood collection fetal DNA research. For some time we know that fetal DNA samples can cross the placental barrier and reach the maternal bloodstream. Therefore, with a simple maternal blood sample can be identified baby DNA characteristics.

The logic behind this examination of fetal sexing is simple. In normal situations, humans have a pair of sex chromosomes. Women have two X chromosomes and men, a Y chromosome and one X chromosome Fetal sexing looking specifically for the presence of the Y chromosome in the mother's blood. Because women are XX, i.e. not have the male Y chromosome in their genetic material, if the examination to find a Y chromosome, it can only come from the fetus.

Therefore, except in exceptional situations, if the examination of fetal sexing find Y chromosome in pregnant blood, it means that the baby is a boy. If not identified the presence of the Y chromosome in the blood, it is because the baby is a girl.

As the pregnancy progresses, more fetal DNA can be found in the maternal circulation. Therefore, the test should only be done from the 8th week of pregnancy. Before the 8th week may not be sufficient amounts of fetal DNA in maternal blood for the identification of the Y chromosome, leading to falsely result of women.

Hit rate of fetal sexing according to gestational age:

Stage of pregnancy	Women	Male
Up to 8 weeks	74.0%	> 99.0%
8th to 10th week	99.0%	> 99.0%

The fetal sexing is superior to ultrasound, it has higher accuracy rate and can determine the baby's sex earlier. Its only downside is the price.

c) Amniocentesis

Amniocentesis is an invasive test that involves inserting a needle into the womb up into the uterus to collect a small amount of amniotic fluid. This liquid collected is rich in genetic fetus material and can be used for the baby's gender identification. His success rate is 100%.

Amniocentesis is a procedure used for research or screening of genetic diseases of the fetus. It has its indications and is never done for identification of sex, since, for that, there are simple tests and with less risk.


It is curious that, despite all the technological advances of recent decades, many people still resort to home tests and time beliefs of their great-grandparents to guess the baby's sex. In fact, as there are only 2 options of sex, male or female, any test, no freak that is, always have a success rate of around 50%. This means that statistically, every second pregnant, any test hit the baby's sex at least 1.

It is also important to highlight the fact that, depending on the culture and the region, the same test can have different meanings. For example, a high belly may mean boy according to popular belief in a particular country, and girl in another. The fun is that in both, the success rate will be 50%.

Let's do a quick review of some critical popular beliefs for baby gender identification.

1. Mother's belly format can identify the baby's sex - MYTH

It is impossible to find out the baby's sex just by pregnant belly format. The format and the mother's belly size have to do with the sex of the baby, but with muscle tone of the abdomen, the mother's body type, size and weight of the baby, the position of the fetus, gestational age and the amount of weight the mother gained during pregnancy.

2. The heart rate of the fetus is different between boys and girls - MYTH

Several studies have tried to establish a relationship between fetal heart rate and their sex, but the vast majority showed no any connection. A 1999 study, however, suggested that in the days before the birth, and only at this time, the heartbeat of the girls are more accelerated than boys. There are other studies that prove this relationship. And even if there were a method that is only able to determine the baby's sex birth a few days is not very useful.

3. The type of motion of an alliance suspended by wire above the womb can identify the sex of the baby - MYTH

This theory is so devoid of scientific basis that no one was willing to do a study on it. It is obvious that the movement of the alliance depends on who is holding, not the womb that has no contact with the object.

In time, it seems obvious, but it never hurts to say, babies are not being endowed with magnetism in order, distance, interfere with the movement of metal objects.

4. Chinese Table based on lunar age detects baby's gender with 99% accuracy - MYTH

Legend has it that a Chinese table of over 700 years, found buried in the tomb of a royal family, can predict, from the lunar age of the mother and the month of conception, the baby's gender with 99% security.

There was no need scientific study to imagine that the table does not work. However, this study there, which provides the scientific proof that the table does not have 99% effectiveness. A Swedish study evaluated the pregnancy of 2.8 million women between the years 1973 and 2006 and reached the following result: the Chinese table has a next hit rate of 50%.