Fetal Sexing Exam: value, where to do it and how it works?

What is the fetal sexing test?

The fetal sex test is a test to identify the baby’s sex even in the 8th week of pregnancy. It is indicated for parents anxious to find out the sex of the baby and who do not want to wait for the ultrasound exam.

The test result is made according to the assessment of the presence (or not) of the Y chromosome in maternal blood. For this, a blood sample from the mother is taken.

It is considered a risk-free, non-invasive examination with few contraindications. Some factors may interfere with the result, but in most cases, the chances of success are 96%.

The test result is revealed within 5 to 7 days when done in the laboratory. In pharmacy fetal sex exams, the result happens in a few minutes. However, the examination is less effective.

What is it for?

Fetal sexing is an examination done to find out the sex of the baby. It is a minimally invasive method, done using a blood sample from the mother.

For parents who are eager to know their child’s biological sex, this test may be an alternative.

The recommendation is that the exam should be done from the 8th week of gestation or the 10th week after the last menstruation. After this period, the hit rate is higher.

It is worth remembering that the fetal sex test is not done to choose the baby’s biological sex . It is also different from embryonic sexing , a technique used in cases of treatment by in vitro fertilization.

This technique basically consists of embryo biopsy and analysis of the embryonic cell to identify the X and Y chromosomes, before being transferred to the uterus .

Unlike fetal sexing, this method is not so simple and liberated. In order for embryonic sexing to take place, there is a whole ethical regulation, since the Federal Council of Medicine prohibits it to be done to choose the sex of the baby or any other biological characteristic of the child.

The exceptions exist when it comes to avoiding diseases that may be related to sex, such as Duchenne muscular dystrophy, for example.

How is done?

Fetal sexing, in general, is a simple exam. It is performed on women with confirmed pregnancy to identify the sex of the baby through the plasma in the mother’s blood.

For this, a blood sample is collected. It is not necessary to be fasting or any other preparation prior to the exam.

For the test, a sample of a maximum of 20mL of blood from the mother is taken, where the DNA of the fetus will be analyzed.

The technique used in this test is called molecular biology, as it allows you to identify sex and analyze your DNA. This is possible because there are fetal cells circulating in the mother’s blood.

Thus, what will be investigated is the presence of the fetus’s Y chromosome in the mother’s blood. When this chromosome is present, the test result determines that it is a boy’s pregnancy, the absence indicates a girl’s pregnancy.

Although the recommendation is that the exam be done after the 8th week, it can be done at any gestational age. It poses no risk to the health of the mother or the baby.

However, the earlier the search for the test, the lower the chances of an efficient result. After the 8th week, when the DNA of the fetus circulates in the mother’s blood, the chances of the test getting the result right can be between 98% to 99%.

How does it work?

After the blood sample is collected, the plasma (liquid part of the blood) is separated and subjected to a process called polymerase chain reaction ( PCR ) with specific primers for the Y chromosome.

This reaction allows to detect even small amounts of fetal DNA present in the plasma, due to its high sensitivity.

The fetal DNA found in the plasma comes from several types of baby cells, however, as the pregnancy progresses, the greater the presence of the genetic material that identifies the sex of the baby in the plasma.

Therefore, the examination seeks to find on the Y chromosome the region called SRY, part of the chromosome that determines the development of the male genitals in mammals. With SRY confirmation, the test determines the baby’s biological sex more accurately.

Sex chromosomes

The sex chromosomes, X and Y, are a type of chromosome responsible for determining biological sex. A chromosome is a DNA sequence with several genes that holds specific actions.

In humans and other mammals, it is the Y chromosome that determines biological sex. Thus, men (or males) have the pair XY and women (or females) have the pair XX. That is why in fetal sexing it is the Y chromosome that defines the result.

Pharmacy fetal sexing test

The pharmacy fetal sexing test is also based on the result of the presence or absence of the Y chromosome. It is much simpler than the fetal sexing test done in a laboratory, however, its percentage of success is lower.

In a test done in the laboratory, an examination of fetal sexing had an accuracy rate of 90%. However, among users, the hit rate was much lower, with an accuracy of 82%.

In order for the chances of the test to be correct, the pregnant woman must wait a little longer, waiting until the 12th week of pregnancy.

The cost of the exam, considering the percentage of error, may not be advantageous for mothers. The average price of the test varies from 100 reais to 150 reais.

How does it work

This test is very similar to pharmacy tests for confirming pregnancy, identifying the sex of the baby through the urine of the pregnant woman.

The test result, unlike the laboratory test, is much faster. In a few minutes, the exam identifies the baby’s gender.

The exam scheme also works by color, being green for a boy and orange for a girl.

The reaction happens through the hormones present in the urine with the chemical crystals of the test.

How to use

The pharmacy fetal sexing test should be done according to the instructions on the product packaging. For the test, the pregnant woman should use the first urine in the morning, because it contains a higher concentration of hormones.

The package contains a syringe without a tip and a small cup with the crystals at the bottom, where the reaction and the test result takes place.

With the syringe, the pregnant woman should collect some of the first urine of the day and then inject the urine into the cup. After gently shaking the contents for approximately 10 seconds, place the cup under a flat surface on top of white paper.

After waiting 5 to 10 minutes, the woman should compare the color of the solution obtained with the indications on the packaging.

When it shouldn’t be done

Many factors influence the result of this examination, therefore, to ensure the effectiveness of the result, some contraindications are put forward. Therefore, the test should not be done under the following conditions :

  • If the pregnancy has exceeded 32 weeks;
  • If the woman has had sex within the past 48 hours;
  • If you have recently undergone infertility treatments, with progesterone-containing drugs;
  • In gestation of twins, mainly in the case of twins of different sexes;
  • In pregnancy made by artificial insemination.

These cases involve factors that interfere with the amount of hormones in the woman’s body and therefore imply the test result.

Contraindications

This examination does not present many restrictions. In general, it can be done by any woman, without posing any risks to her health or the health of the fetus.

The existing contraindications are related to the exam result. Some factors can interfere with the effectiveness of the test, so it is recommended that women do not do it in the following circumstances:

Blood transfusion or transplants

The fetal sex test is not recommended for women who have had a transplant or who have already had a blood transfusion.

It has been reported that blood donor cells can interfere with the test result, enabling a false biological male sex result for the fetus.

Before the 8th week of gestation

Women with such a recent pregnancy may get an inadequate test result, so it is advisable that the fetal sex test be done after the 8th week of pregnancy.

Fetal sexing at twin pregnancy

The fetal sexing exam can be performed in the pregnancy of twins, however, the result can have different interpretations, being different for univitheline and bivitheline twins:

Univitelinos

In cases where there is a pregnancy of twin twins, where the fetuses share the DNA and therefore have the same sex, the result of the fetal sex test determines the sex of both.

Thus, if the test identifies a pregnancy of male fetuses, it applies to both. If the Y chromosome is absent, it means that they are both girls.

Bivitelinos

When it comes to bivithelin twins, the test result is less effective, as it means that the fetuses do not share the same placenta. Therefore, it does not mean that they will be of the same sex or that they will have similar physical characteristics.

Therefore, the result of the fetal sex test should be interpreted as follows:

  • The presence of the Y chromosome determines that at least one of the babies is male;
  • The absence of the Y chromosome determines that it is a pregnancy of two girls.

What can affect the results?

Fetal sexing is an error-prone test like any other test. Even with a relevant percentage of correct answers, when it comes to the laboratory exam, there are some factors that imply the result.

Therefore, in view of certain factors, pregnant women may receive a wrong result. Are they:

Multiple pregnancy

When it comes to multiple pregnancies, 2 or more embryos, the result is not guaranteed. In the case of a twin pregnancy, it is still possible that the test identifies the sex of one of the babies, as a boy, or of the two fetuses when it comes to girls, but it is still not 100% safe.

Nothing prevents these women from taking the test, but to ensure a more real result, it may be more advantageous to wait a little longer and perform tests such as ultrasound.

Subclinical abortion

Subclinical abortion, or spontaneous abortion, can affect the test result when it occurs in a multiple pregnancy, where one or more embryos, as a result of a process of hyperovulation or in vitro fertilization, end up dying.

The DNA of the aborted fetus can be detected in the mother’s blood within two weeks after the abortion. In the case of a spontaneous abortion of a male embryo, the test result becomes inconsistent.

Blood transfusion and transplants

Pregnant women who have a history of transplantation or blood transfusion should be aware of the possible interference of these factors in the test result.

Scratchs

The examination of fetal sexing does not present complications for the health of the mother or for the fetus. Therefore, it can be done without fear of risk.

The only concern is how the blood will be collected. The materials used and the place where the exam will be performed must be clean and free from contamination.

Price

The price of a fetal sex test varies according to the laboratory and region of the country where it is performed. The average is between 260 reais and 850 reais, and may have higher values.

The cost is higher when compared to the average price of the pharmacy fetal sexing test, with an average of 100 reais to 150 reais.

It is not an exam offered free of charge by the Unified Health System (SUS) nor is it covered by health plans, as it is not considered an urgent exam.

Complementary exams

In addition to the fetal sexing test, there are other alternatives to find out the sex of the baby. Know which ones:

Ultrasound

Ultrasound is a simple and non-invasive image exam. It is considered the most conventional way of identifying the baby’s sex. It is part of prenatal care and has other functions, the identification of sex being one of the exam evaluations.

Like the fetal sexing test, obstetric ultrasound poses no risk to the mother or the fetus. The identification of sex is done through the observation of the genitalia through the image.

This identification is not always easy, because for the doctor to be able to clearly see the presence of the male or female genital organ, the baby needs to be in a favorable position for this.

The differentiation of the genitalia can be done close to the 6th week of pregnancy, but it is from the 21st week that ultrasound is recommended to identify the baby’s sex. This ultrasound is called a morphological ultrasound.

However, even this exam is subject to error. Even with complete genitalia, the position of the fetus in the mother’s belly can prevent visibility during ultrasound.

Amniocentesis

Amniocentesis is an invasive test that does not have the sole purpose of designating the sex of the baby.

The test consists of inserting a needle into the pregnant woman’s belly until it reaches the uterus, where a small amount of amniotic fluid is collected.

This liquid is rich in genetic material and contributes to the investigation or screening of genetic diseases in the baby. Because it contains a large amount of genetic material from the fetus, the biological sex hit rate is 100%.

However, it should be done only in special cases with the doctor’s indication. For the knowledge of the baby’s sex, there are simpler and safer tests.

Common questions

Many doubts arise when the subject involves a pregnancy. In the case of the fetal sex test, it is no different. Here are some frequently asked questions on the subject:

Do previous pregnancies interfere with the result?

No, the fact that the pregnant woman has other children does not interfere with the test results, whether they are female or male. After delivery, within hours, the fetal DNA is eliminated from the mother’s circulation.

How long does it take for the result?

The result of the laboratory exam takes 5 to 7 days for the result. The pharmacy test reveals the sex of the baby in a few minutes.

How long does this exam take?

This examination is not time consuming. As it does not require any special care before or after the procedure, the time needed is only the time in which the blood is collected, as in a common blood test.

Is the test result safe?

Yes, although about 5% of the tests may be inconclusive, requiring a second blood collection and writing the test, the fetal sex test is quite accurate. This, of course, when we eliminate all possible factors that interfere with the exam.

Is the fetal sexagel test able to detect a possible pregnancy?

No, the fetal sexagel does not work as a pregnancy test. Women who have any symptoms of pregnancy should look for other tests to confirm this chance, such as the Beta-HCG blood test.

What is the result of a fetal sex test when there is no pregnancy?

As seen earlier, the fetal sex test is not a test to confirm pregnancy.

However, if women who are not pregnant take the test, the result will be that of a girl’s pregnancy.

Therefore, before performing this exam, it is necessary to be sure if there is a pregnancy, as there will be a result.

Is the test able to identify diseases or abnormalities in the baby?

No, the fetal sex test is not yet able to detect genetic diseases or abnormalities in the fetus. However, there are studies that show interest in exploring the applications of fetal DNA found in the plasma contained in the mother’s blood sample.

This possibility would allow the non-invasive diagnosis of diseases such as beta- thalassemia , a hereditary type of anemia , dwarfism and Down’s syndrome. Thus, it would dispense with the use of amniocentesis, an invasive process for collecting amniotic fluid, and chorionic villus biopsy, where there is a sample of the placenta.

Are pre-exam and post-exam care necessary?

No, the fetal sex test is considered simple. No specific care is needed before or after it is done.

Can the fetal sex test only be done by medical advice?

No . To perform the fetal sexing exam, a medical prescription is not necessary. However, this may vary depending on the laboratory. Before scheduling the test, you need to check for this requirement.

How do I know how many weeks I am pregnant?

To know the gestational age, the pregnant woman needs to know the date of her last menstruation. After 7 days of this date, a week of gestation is counted.

For example, if a woman had her last period beginning on January 1, the gestational age should be counted from that date and not the day of the last sexual intercourse.

From the example above, the woman should have a fetal sex exam after March 12, when her gestational age would be more than 10 weeks after the last menstrual period.

This method is used because it is difficult to define precisely when fertilization happens, as sperm can survive for up to 7 days in the woman’s body before fertilizing the egg and the pregnancy is, in fact, started.

However, not all women have regular periods or remember the date of their last period. In these cases, to know the gestational age, the woman can ask the doctor during an ultrasound at the prenatal consultation.

It is a more accurate way of knowing how many weeks you are pregnant and the approximate date of delivery.

It is also possible to consult the gestational week through the uterine height (AU), where the doctor uses a tape measure to measure whether the growth is adequate for the time of pregnancy.

Normally, uterine height corresponds to gestational age, as for example a pregnant woman at 26 weeks of gestation, where the AU must be 25 cm.

Another factor considered to calculate gestational age is the amount of Beta HCG in the blood.

Does the use of medications interfere with the result?

Generally speaking, no. In specific cases, such as the use of antibiotics or antiviral drugs, medications can interfere with the sensitivity of the test and influence the result.

When the fetal sex test is done to search for any pathology in the fetus, it is also possible that the use of some medications may interfere.

So that this does not happen, inform the medications you are taking before carrying out the test and check the need to change or discontinue use.


The fetal sex test is an alternative for those who want to find out the sex of the baby without waiting too long. If you have already taken this exam, let us know what the experience was like in our comment space. Thanks for reading!

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