About 95% of chromosomal disorders, especially those of trisomy (when the chromosome pairs have an extra chromosome), are found during the examination.
Of these, 50% occur due to trisomy of chromosome 21 (Down syndrome), 25% due to trisomy of chromosome 18 (Edwards syndrome) or 13 (Patau syndrome), 10% due to Turner syndrome (women are born with only one chromosome X) and 10% derived from other chromosomal changes.
Chromosomes are formed by DNA and are found in the nucleus of the cell. The normal thing is that each person has 23 pairs of chromosomes, making a total of 46. Its function is to transport the necessary information so that the cells can develop and reproduce.
It is worth mentioning that parents are not to blame for this condition. The onset of chromosomal problems has adverse and unforeseen causes.
Advanced maternal age (over 35 years) is considered dangerous because it increases the child’s risk of having Down’s Syndrome. However, in only 30% of fetuses affected by the disease, the mother is in this age group. This is because, despite the lesser threat, in young women the fertility rate is higher.
The most common pathologies include:
Down syndrome, trisomy 21 or DS, as it is also known, is defined by the existence of three chromosomes 21 in the cells instead of two. The disorder affects 1 in every 700 babies. In Brazil, 270 thousand people have the syndrome.
Not all people have the features normally associated with the syndrome, such as different facial appearance and developmental delay, or manifest them to the same degree. However, the intellectual deficit is a common point among all carriers.
Identified by the British geneticist John H. Edwards in 1960, Edwards syndrome, or trisomy 18, is characterized by the copy of three chromosomes 18. It is the second most recurrent trisomy after birth, second only to Down syndrome. About 1 in 8,000 children have the genetic error.
There are several indications of Edwards syndrome, such as crossed legs and physical anomalies – cranium more elongated in the occipital region (back), small mouth, short neck, index finger larger than the others and low muscle mass at birth. In addition, there is a developmental and mental retardation.
There is no treatment for trisomy 18. In 95% of cases, the woman has an abortion. It is estimated that half of newborns die in the first year of life. The rest can live up to 4 years of age.
Patau syndrome is a trisomy 13, that is, there is a third chromosome 13. It was defined by the geneticist doctor Klaus Patau in the year 1960. It is estimated approximately 1 case for 12 thousand births. In 40% of them, the pregnant woman is over 35 years old.
The syndrome causes severe mental retardation, cardiac and urogenital problems, as well as severe malformation in the nervous system and organs (opening or cracks in the roof of the mouth and lips, deformity in the eyes and ears).
Like Edwards’ Syndrome, it is fatal: of the 2.5% who are born alive, 45% of babies die at 1 month of age, 70% at 6 months and only less than 5% make it past 3 years of age. The longest experience ever recorded was 10 years.
Cardiac malformations are related to the complete lack of development of the ventricles, valves and major arteries of the heart. In most cases, the causes that lead to the changes are not known. About 5 in every 100 births have some type of congenital heart problems.
However, the use of medication for seizures or psychiatric problems, illicit drugs and excessive alcohol consumption in early pregnancy can impair the development and constitution of heart structures.
Diabetes and heredity are also factors that contribute to the appearance of heart problems.
From the fourth and eighth weeks of gestation, the organs and systems of the baby’s body begin to develop. The heart builds and connects with the blood vessels. At the end of the seventh week, the heartbeat begins.
However, ultrasound is only possible from week 12, when the basic structures of the heart become noticeable and, thus, can point out abnormalities.
Among them are:
Left Heart Hypoplasia Syndrome
Left Heart Hypoplasia Syndrome (HCL) or Left Ventricular Hypoplasia is responsible for 8% of occurrences of congenital heart diseases. This condition is uncommon, affecting 1 in every 5 thousand newborns.
In this situation, the left side of the heart does not develop properly in the baby while still in the mother’s womb. Consequently, it is not possible to pump blood to the body satisfactorily.
Treatment consists of cardiac surgery in the first years of life or transplantation. If these procedures are not performed, the chances of the child dying after birth are 95%. There is no cure for HCL, requiring medical follow-up for the rest of your life.
Fetal tachycardia is characterized by a steady fetal heart rate above 160 beats per minute. It is a rare circumstance, occurring in 0.4 to 0.6% of pregnancies.
If the problem is not resolved, it can trigger:
- Cardiac insufficiency;
- Fetal hydrops (accumulation of fluid in certain areas of the baby’s body, such as the lungs, heart and abdomen);
- Neurological morbidity (cerebral palsy, mental retardation, autism, among others);
- Fetal death, when the fetus dies inside the uterus from the 20th week.
Treatment is done via medication, which can be maternal or intrauterine.
In a physical state, the impulse generated in the atria must go to the ventricle to effectively generate the heartbeat. The atrioventricular node is the means of connection between them.
Atrioventricular block occurs when the impulse fails to advance through the node, which may be only a delay or total restriction. As a consequence, the baby suffers low heart rate at birth.
The mortality rate is 85%, which is why it is important to find a problem even in prenatal care. Depending on the severity, treatment consists of artificial stimulation using a pacemaker, implanted in the neonatal period (from birth to 28 days).
How is done?
The nuchal translucency exam can be done through transvaginal ultrasonography (in cases of obesity or when the uterus is tilted back) or abdominal.
Such procedure can be performed in hospitals, laboratories or even in the obstetrician’s office. The size of the fetus will be measured, from the head to the buttock. Subsequently, the nuchal translucency measurement.
Another alternative is to perform a morphological ultrasound in the first months of pregnancy, which will consider, in addition to the previous information, conditions such as maternal age and history of other children with Down syndrome.
As the size of the uterus is still quite small in early pregnancy, it is difficult to have a satisfactory image by abdominal ultrasound, hence the need for a transvaginal examination. However, it can also be done during the entire pregnancy, without injuring the mother or baby.
Transvaginal ultrasound, also known as endovaginal or intravaginal ultrasound, allows visualization of the uterus, ovaries and fallopian tubes by means of images. The process is simple, painless and takes no time (around 10 to 15 minutes).
The images are formed by introducing the ultrasound probe – a thin tube, 2 cm in diameter, wrapped in a condom and lubricating gel.
High frequency sound waves are transmitted, which capture the echo generated by the organs, and are subsequently interpreted by the computer.
Anesthesia is not necessary for this method, which is less annoying than Pap smears ( cervical cancer prevention exam ). The probes used must comply with the cleaning and sterilization rules.
The woman’s comfort and privacy are prioritized through the use of a dress during transvaginal ultrasound and a large towel, which will be superimposed on the lower part of the body.
Abdominal ultrasound is also an easy method, which provides images of the uterus, the placenta and the baby through a device called a Piezoelectric Transducer.
Just like vaginal ultrasound, the direct contact of the device with the abdominal region perceives the echo of these regions that are transferred to the computer.
For this, a portion of gel is placed in the lower region of the belly. The gel helps the contact between the probe and skin. It does not cause pain, but the patient may feel pressure due to the transducer on her belly.
It is preferable that the morphological ultrasound is performed during the 20th and 24th weeks of gestation, as the baby can be seen in full and with greater ease. What differentiates it from abdominal ultrasound is the quality of the image and the wealth of details granted.
Evaluation of internal organs, veins and arteries of the brain and heart, in addition to bones are some of the uses of the exam. It is also possible to find out the position of the placenta, as well as its condition.
When to do it?
The nuchal translucency exam should be done when the fetus is between 45mm and 84mm in length, measuring from the head to the buttock, which is equivalent to the period between 11 to 14 weeks of gestation.
Among the justifications, there is the possibility of interrupting pregnancy in the first three months and the high level of perception of chromosomal changes, which reaches 98% to 100%.
After 14 weeks, the percentage of correctness drops to 90%, since the volume of the fluid changes, becoming smaller, and is no longer transparent in the ultrasound image. In addition, the fetus changes to a vertical position, making it difficult to capture the image.
For a more accurate result, doctors advise that the analysis should be done after 12 full weeks.
Because it is a non-invasive exam, nuchal translucency has no contraindications .
Pre-examination and post-examination care
Pre-examination care is few and varies according to the examination method. In the case of transvaginal ultrasound, the recommendations are:
- As it is an intimate area, take care of your personal hygiene;
- At the time of the examination, a hospital gown will be worn. So, go with comfortable and easy to take off clothes;
- Have an empty bladder.
It is important that you notify your doctor in case of sensitivity or allergy to latex. To predict possible risks, the doctor may also order a blood test between 10 and 12 weeks of gestation.
In abdominal ultrasound, precautions include:
- Drink 4 to 6 glasses of water in advance, as the belly should be full but not uncomfortably. This facilitates the verification of the abdominal walls and their interior;
- Fasting for 6 to 8 hours. The measure reduces gases in the intestine, which can cause difficulty in visualizing the abdomen;
- Wear comfortable clothes that facilitate access to the abdominal region.
After the exams, there is no need for any physical rest, you can return to your daily activities normally.
The measurement, to be considered normal, must be less than 2.5 millimeters . If the value found is equal to or higher than this number, there is a greater chance that the fetus will present some type of disorder.
The exam provides about 80 to 90% accuracy. In cases of Down syndrome, 77% are identified. This means that other patients with the syndrome show normal results in the procedure.
If there is increased nuchal translucency, but normalization of the chromosomes, it may be a sign of genetic syndromes and malformations of the heart and the fetus itself, culminating in spontaneous abortions or intrauterine death.
The false positive result of measuring nuchal translucency occurs 5% of the time, that is, 1 in 20 women receive the incorrect information.
Depending on the amount of fluid in the baby’s neck, the results of NT can be:
To be considered normal, the nuchal fluid must be less than 2.5 millimeters.
When the liquid in the neck of the fetus is equal to or greater than 2.5 millimeters, the result is considered altered or increased.
How is the risk calculated?
In certain tests, instead of the terms “normal” and “increased”, the result is presented based on the risk of chromosomal dysfunctions. It can be calculated using a computer program, using information from the Fetal Medicine Foundation – in Portuguese.
Apart from the results of nuchal translucency, the ideal is to take into account other aspects, in addition to adapting the calculated risk for this specific program.
Risks, more recently, are classified as:
- Low risk : less than 1 in 1000;
- Intermediate risk : between 1 in 50 and 1 in 1000;
- High risk : greater than 1 in 50.
The aim of these new categories is to increase the number of non-invasive prenatal tests (NIPT), which in turn, encounter trisomies from 21, 18 and 13, in addition to decreasing the occurrences of invasive tests, which can lead to abortion.
However, many radiological mechanisms are still based on the old risk categories:
- Low risk : less than 1 in 300;
- High risk : greater than 1 in 300.
In the result of the exam, there are two analyzes, the “ fund risk ” and the “ adjusted risk ”. In the first, which serves as a starting point, only the age of the mother and baby (gestational period) will be observed. If there are chromosomal changes in the previous child, the chances are higher for subsequent pregnancies. The result is presented in numbers, for example, 1 in 300.
In the second, the nuchal translucency measurement and blood tests are evaluated in order to calculate the baby’s individual risk. In this case, the result is classified by the grade (high, intermediate or low). About 5% of women are at high risk in the combined test in the first three months of pregnancy .
Most of the babies who received the high-risk probability did not, in fact, have chromosomal defects and for most future mothers who underwent diagnostic tests, there were normal results.
How to interpret the results
The results will be disseminated through the baby’s probability of having a chromosomal dysfunction. Therefore, he can be confused, needing the help of a health professional to assist the mother in understanding.
For example, a pregnant woman may be told that her child has 1 in 30 or 1 in 4000 chances of having Down Syndrome. This means, in the proportion 1 in 30, that for every 30 women with the same description, 1 baby will carry the disease.
Already in the estimate 1 in 4000, it means that 1 of these 4000 babies will have the syndrome and 3999 will not. Therefore, the higher the number, the lower the risk of the baby having Down Syndrome.
It can also be stated that the results are “normal” and “abnormal”, according to a margin defined by the test.
It is worth mentioning that the figures presented only reveal which babies are likely to have chromosomal abnormalities, but that they do not necessarily have it.
Factors to consider
In certain situations, the baby may manifest chromosomal diseases and still the result of nuchal translucency results in normal. To improve the hit estimate, other factors must be assessed. Together, they add up to 98% accuracy.
If the mother is over 35, the chances of the baby having malformation increase.
The patient’s history is checked to see if there have been cases of syndromes and heart disease in the family.
Absence of nasal bone
The nasal bone is composed of two thin bones that form the “bridge” of the nose. About 1% to 3% of normal fetuses do not have it. In cases of syndrome, its absence indicates 60% of cases of trisomy 21 and 40% to 50% of trisomies 18 and 13.
The perception of nasal bone, assessed in conjunction with other factors that determine the degree of risk, allows for greater precision and identification of trisomy 21 (from 90% to 93%), in addition to reducing the number of false positives in this case.
Change in venous duct flow and tricuspid reflux
Changes in the venous duct (fetal blood vessel) and tricuspid reflux (when the tricuspid valve is not closed, partial blood reflux to the right atrium occurs) are indicative of heart disease or Down syndrome.
Change in biochemical examination (PAPP-A and free Beta HCG)
When Down’s syndrome is not identified by the nuchal translucency test, 50% are recognized through the biochemical study in women. PAPP-A and free Beta HCG can be administered before, during or after ultrasound.
Both the mother and the baby are not at risk. The probe inserted during transvaginal ultrasound does not reach the cervix, therefore, it does not hurt the fetus.
In addition, the high frequency waves emitted from the devices used during the examination are inaudible to the human ear.
What is the value of the exam?
The value of the nuchal translucency exam varies according to the location performed, and can range from 100 to 400 reais. However, it can be done free of charge by SUS when referred by the obstetrician.
Taking into account the results of nuchal translucency, maternal age and the absence or absence of nasal bone, complementary exams, such as non-invasive prenatal test (NIPT), amniocentesis or chorionic villus biopsy, may be requested.
However, even if the results are positive, the fetus can still have other diseases. Therefore, fetal echocardiography may also be ordered.
Noninvasive prenatal testing (NIPT)
The non-invasive prenatal test (NIPT) is performed by means of a blood test and, optionally, fetal sexing, that is, the identification of the baby’s sex, can be included.
The objective of the NIPT is to define the risks of trisomies, especially at 21, 18 and 13, by the amount of chromosomes present in the mother’s blood. This test has 99% correct diagnosis and only 0.1% false positive.
Because it is an aggressive test, amniocentesis is only indicated when there are signs of problems with the baby. 1 in 100 women undergo abortion due to the procedure.
With the aid of ultrasound, the doctor will remove the amniotic fluid through a long needle inserted into the mother’s belly. The material contains fetal cells, substances and microorganisms that will be analyzed.
Through collection, it is possible to detect genetic or congenital changes accurately. The use or not of anesthesia should be discussed with the specialist. The intensity of abdominal pain varies for each patient.
Chorionic villus biopsy
Chorionic villus biopsy aims to identify genetic diseases in the baby. The exam consists of removing a small sample of tissue from chorionic villi (placenta) through the cervix or abdomen, in order to check the genes and chromosomes.
The analysis is done at 11 to 12 weeks of pregnancy. Anesthesia is not necessary, however, the woman may experience discomfort similar to menstrual pain and bleed. In this procedure, there is also a risk of miscarriage.
The echocardiography fetal complement is a morphological ultrasound. It does not pose risks for the baby or the mother, as it is an ultrasound similar to those made previously.
The professional will specifically examine the development, physical characteristics and work done by the fetus’ heart during pregnancy. Early diagnosis and treatment while still in the uterus significantly increase the chances of improving the condition.
What do you mean when the chance of Down Syndrome is 1 in 300?
When the estimates passed on to the pregnant woman are 1 in 300, it means that, of the 300 women with the same result, 1 of them will have their child with Down. However, this number varies according to the type of calculation and the test that was applied. The higher the second number, the lower the risk of the disease.
In some cases, the nuchal translucency measurement is above the 99th percentile, which may indicate risks of congenital heart problems. Therefore, the mother may undergo fetal echocardiography.
Morphological ultrasound, performed from 20 to 24 weeks of gestation, is another means used to find Down’s Syndrome.
What to do when the baby has increased nuchal translucency?
When the accumulation of fluid in the baby’s neck is abnormal, consult the doctor and follow his recommendations. Among the procedures performed, are amniocentesis or chorionic villus biopsy, which are used to diagnose the problem.
Through them, it is possible to investigate the baby’s chromosomes. Even with normal results, the fetus can still present other disorders, such as cardiac malformations.
Therefore, it may also be recommended that a morphological ultrasound and fetal echocardiography be performed, which allow for a more detailed analysis.
Remembering that the change in the nuchal translucency does not determine that the child will have Down. The same happens with results below the stipulated value, which present lesser risks, but are not completely discarded.
Is nuchal translucency done by the belly?
One of the methods used to perform the nuchal translucency exam is abdominal ultrasound, in which the equipment comes into contact with the skin of the belly, generating the image.
However, in some cases, the measurement of the amount of nuchal fluid can also be perceived through transvaginal ultrasound.
Nuchal translucency is a test that measures the amount of fluid in the baby’s neck. The procedure is not a diagnosis, it only allows assessing whether the fetus is at risk of developing congenital or genetic problems.
However, if any changes are found, additional tests may be ordered to determine the disorder.