Ultrasound to check for down syndrome
Prenatal Testing for Down Syndrome | Patient Education
Down syndrome is a genetic condition caused by extra genes from the 21st chromosome. It results in certain characteristics, including some degree of cognitive disability and other developmental delays. Common physical traits include an upward slant of the eyes; flattened bridge of the nose; single, deep crease on the palm of the hand; and decreased muscle tone. A child with Down syndrome, however, may not have all these traits.
The incidence of Down syndrome in the United States is about 1 in 1,000 births. There is no association between Down syndrome and culture, ethnic group, socioeconomic status or geographic region.
Age-Related Risks
Generally, the chance of having a Down syndrome birth is related to the mother's age. Under age 25, the odds of having a child with Down syndrome are about 1 in 1,400. At age 35, the odds are about 1 in 350. At age 40, the odds are about 1 in 100.
Causes of Down Syndrome
There are three causes of Down syndrome:
Trisomy 21
An estimated 95 percent of people with Down syndrome have trisomy 21, meaning they have three number 21 chromosomes instead of two. We normally have 23 pairs of chromosomes, each made up of genes. During the formation of the egg and the sperm, a woman's or a man's pair of chromosomes normally split so that only one chromosome is in each egg or sperm. In trisomy 21, the 21st chromosome pair does not split and a double dose goes to the egg or sperm. An estimated 95 to 97 percent of the extra chromosome is of maternal origin.
Translocation
Translocation occurs in about 3 to 4 percent of people with Down syndrome. In this type, an extra part of the 21st chromosome gets stuck onto another chromosome. In about half of these situations, one parent carries the extra 21st chromosome material in a "balanced" or hidden form.
Mosaicism
In mosaicism, the person with Down syndrome has an extra 21st chromosome in some of the cells but not all of them. The other cells have the usual pair of 21st chromosomes. About 1 to 2 percent of people with Down syndrome have this type.
Prenatal Testing
Screening tests can identify women at increased risk of having a baby with Down syndrome.
These tests have no risks of miscarriage, but can't determine with certainty whether a fetus is affected. Diagnostic tests, on the other hand, are extremely accurate at identifying certain abnormalities in the fetus, but carry a small — generally less than 1 percent — risk of miscarriage. We offer options for both screening and diagnostic testing.
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Screening Tests
Sequential Integrated Screening — Sequential integrated screening is offered to all pregnant women by the state of California. This non-invasive screening is performed in two steps.
In the first step, which is performed between 10 and 14 weeks of pregnancy, a blood sample is taken from the mother and a nuchal translucency ultrasound is performed to measure the amount of fluid at the back of the baby's neck. If the blood test is scheduled prior to the ultrasound, we can provide the results at the end of the ultrasound appointment. The results of the blood test, the nuchal translucency measurement and the mother's age are used to estimate the risk for Down syndrome and trisomy 18.
The second step is a maternal blood test between 15 to 20 weeks of pregnancy. When the results of this blood test are combined with the results from the first trimester blood test and nuchal translucency ultrasound, the detection rate for Down syndrome increases. This test also provides a personal risk assessment for having a fetus with trisomy 18, Smith-Lemli-Opitz syndrome, an open neural tube defect or an abdominal wall defect.
Diagnostic Tests
Amniocentesis, chorionic villus sampling (CVS) and ultrasound are the three primary procedures for diagnostic testing.
Amniocentesis — Amniocentesis is used most commonly to identify chromosomal problems such as Down syndrome. When the fetus is known to be at risk, it can detect other genetic diseases like cystic fibrosis, Tay-Sachs disease and sickle cell disease.
An amniocentesis procedure for genetic testing is typically performed between 15 and 20 weeks of pregnancy. Under ultrasound guidance, a needle is inserted through the abdomen to remove a small amount of amniotic fluid.
The cells from the fluid are then cultured and a karyotype analysis — an analysis of the chromosomal make-up of the cells — is performed. It takes about two weeks to receive the results of the test.
Amniocentesis detects most chromosomal disorders, such as Down syndrome, with a high degree of accuracy. Testing for other genetic diseases, such as Tay-Sachs disease, is not routinely performed but can be detected through specialized testing if your fetus is known to be at risk. Testing for neural tube defects, such as spina bifida, also can be performed.
There is a small risk of miscarriage as a result of amniocentesis — about 1 in 100 or less. Miscarriage rates for procedures performed at UCSF Medical Center are less than 1 in 350.
Chorionic Villus Sampling (CVS) — Like amniocentesis, chorionic villus sampling is used most commonly to identify chromosomal problems such as Down syndrome. It can detect other genetic diseases like cystic fibrosis, Tay-Sachs disease and sickle cell disease in at-risk fetuses.
The main advantage of CVS over amniocentesis is that it is done much earlier in pregnancy, at 10 to 12 weeks rather than 15 to 20 weeks.
CVS involves removing a tiny piece of tissue from the placenta. Under ultrasound guidance, the tissue is obtained either with a needle inserted through the abdomen or a catheter inserted through the cervix. The tissue is then cultured and a karyotype analysis of the chromosomal make-up of the cells is performed. It takes about two weeks to receive the results.
The advantage of CVS over amniocentesis is that the test is performed much earlier in pregnancy, so results are typically available by the end of the third month. A disadvantage is that spinal cord defects cannot be detected. Expanded alpha fetoprotein (AFP) blood testing or ultrasound can be performed later in the pregnancy to screen for spinal cord defects.
There is a small risk of miscarriage as a result of CVS — 1 in 100 or less. Miscarriage rates for procedures performed at UCSF Medical Center are less than 1 in 350.
Ultrasound — The primary purpose of ultrasound is to determine the status of a pregnancy — the due date, size of the fetus and if the mother is carrying multiples. Ultrasound also can provide some information about possible birth defects in a fetus. All patients at UCSF Medical Center undergo a comprehensive ultrasound examination before any invasive tests are performed. Results of the ultrasound are explained at the time of the visit.
In some patients, an ultrasound raises concern of a possible abnormality in the fetus. We have extensive experience in performing and interpreting ultrasounds in pregnancy.
If You Receive a Positive Result
If you receive positive results on a screening test, we recommend that you discuss this with your doctor and a genetic counselor. Options for further diagnostic testing will be explained. The decision as to whether to have invasive genetic testing is up to you.
If a diagnostic test finds a genetic abnormality, the significance of such results should be discussed with experts familiar with the condition, including a medical geneticist and a genetic counselor, as well as your own doctor.
Screening for Down syndrome | Pregnancy Birth and Baby
Screening for Down syndrome | Pregnancy Birth and Baby beginning of content5-minute read
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If you or someone you care about has a child with Down syndrome, or is pregnant with a Down syndrome baby, you may have many questions or feel overwhelmed by what this means. The most important thing that babies with Down syndrome need — just like any baby — is a loving, secure environment in which they feel nurtured and supported.
What is Down syndrome?
Down syndrome is the most common chromosomal condition that a baby can be born with. Around 1 in every 1,000 babies born in Australia has Down syndrome.
Down syndrome is also known as Trisomy 21. People with Down syndrome usually look different from other people and may have some difficulty learning new things.
What causes Down syndrome?
Normally, every cell in the human body — except egg and sperm cells — has 46 chromosomes. The egg and sperm cells normally have 23 chromosomes each.
The most common cause of Down syndrome is when an extra copy of chromosome 21 randomly appears in either the egg or sperm. At conception, when the egg and sperm meet, the extra copy of chromosome 21 grows throughout all of the embryo’s cells, giving them each 47 chromosomes instead of the usual 46.
Less commonly, the extra copy of the chromosome can appear in some of the embryo’s cells after conception. This is called mosaicism and results in some cells having 46 chromosomes and some having 47.
Another rare form of the syndrome is caused by ‘Robertsonian translocation’. This occurs when a piece of chromosome 21 breaks off and becomes joined to another chromosome before or after conception. In this case, the embryo’s cells will all have 46 chromosomes, but each cell still contains an extra copy of chromosome 21.
What are the most common features of Down syndrome?
Many babies with Down syndrome have one or more of the following features at birth:
- low muscle tone ('floppy' muscles)
- a flatter face with eyes slanting upward
- small ears and a wider neck than usual
- a single crease across the palm of the hand
- a gap between the first and second toes
Down syndrome is also associated with intellectual disability.
However, not everyone with Down syndrome will have all of these features.
What medical complications might come with Down syndrome?
About 1 in every 2 babies born with Down syndrome will have heart problems and approximately 1 in 10 will have gastrointestinal (gut) problems. Hearing and vision problems are also more common in people with Down syndrome.
How is Down syndrome diagnosed?
Pregnant women are offered routine antenatal tests at different times during pregnancy and for different reasons.
These include screening tests, such as ultrasounds and blood tests, that can help estimate your baby’s risk of being born with a range of conditions, including Down syndrome.
Non-invasive prenatal testing (NIPT) is a new blood test that can be done as an alternative screening test.
Diagnostic tests (such as chorionic villus sampling or amniocentesis) will show whether a baby actually has Down syndrome.
After the baby is born, chromosome testing from a blood sample, may be done to confirm Down syndrome.
What is the treatment for Down syndrome?
There is currently no way to prevent or cure Down syndrome. Prenatal testing allows you and your family to make informed decisions, including ending the pregnancy. For this reason, before you have the test it’s a good idea to think about why you are choosing to do it, and how you will feel once you get the results.
Consider also who you want to discuss any important decisions with — your partner, a friend or family member, or a health professional such as your doctor or midwife are all good options.
Early diagnosis can also help you and your doctor continue to check your baby for complications and to act early if needed. Some people with Down syndrome may need surgery to repair heart defects or gut blockages. Medicines to treat thyroid disease may also be needed in some cases.
Children all learn and develop at their own pace. However, there are effective early intervention programs for children with Down syndrome that can help them reach their learning potential.
Resources and support
Down Syndrome Australia provides support, information and resources for people with Down syndrome and their families across Australia.
Support services include:
- information and advice about Down syndrome
- information about local support groups
- home visits
- new parent packs
- workshops and webinars
- online support groups for you and your family
A national phone number (1300 881 935) can connect you with your local state or territory Down syndrome organisation for further information.
Speak to a maternal child health nurse
Call Pregnancy, Birth and Baby to speak to a maternal child health nurse on 1800 882 436 or video call. Available 7am to midnight (AET), 7 days a week.
Sources:
Centre for Genetics education (Trisomy 32 - Down Syndrome), Lab Tests Online (Down syndrome), Down Syndrome Australia (Prenatal and New Parent)Learn more here about the development and quality assurance of healthdirect content.
Last reviewed: March 2022
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Related pages
- Caring for a child with Down syndrome
- What is Down syndrome?
- Questions to ask your doctor about tests and scans
- Routine antenatal tests
- Pregnancy checkups, screenings and scans
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Diagnosis of Down's syndrome according to ultrasound, timing of the examination, signs of fetal chromosomal pathology
It is possible to diagnose Down's syndrome already in the early stages of pregnancy according to ultrasound examination (ultrasound) of the fetus . The method is based on the use of high-frequency sound, which is reflected from various surfaces with different intensities.
Deciphering the signals allows the doctor to create a two-dimensional image of the internal structure of the area under study.
Is it possible to detect Down syndrome by ultrasound
Down syndrome in the fetus is diagnosed by ultrasound in 60-90% of cases. High accuracy of the examination is achieved by comparing the development of the fetus with the norm. In addition to Down syndrome, ultrasound can detect signs of a number of other genetic malformations. Pathologies in the structure of the heart, incomplete rotation of the intestine, duodenal atresia can also serve as signs of Down syndrome in the fetus, all these malformations are recorded by ultrasound.
Tests before marriage
Down syndrome is observed in one case in 700-800 pregnancies and is characterized by the presence of an extra 21st chromosome. The syndrome affects the future life of the child.
The possibility of having a child with Down syndrome increases with the age of the parents.
In addition, the risk of a chromosomal abnormality increases significantly if one of the parents already has Down syndrome. In some cases, the pathology is mosaic in nature and may be invisible even to very close people.
Down's syndrome is reliably diagnosed in the perinatal period using ultrasound and a number of other methods.
How does Down syndrome manifest itself after birth?
Children with Down syndrome have a number of external differences. Their faces are flatter, with a slightly pronounced bridge of the nose and an epicanthal fold at the inner corners of the eyes. The skull of the child is shortened, with a flat occiput.
After birth, children with Down syndrome are somewhat behind in physical and mental development. Over time, the mental retardation, in comparison with other children, will be more and more noticeable.
In addition, people with Down syndrome are more likely to suffer from congenital heart defects (occur in almost 40% of cases).
The presence of an extra chromosome significantly increases the risk of developing some other diseases: cataracts, Alzheimer's, myeloid leukemia, and often there are disorders in the digestive system. Weakened immunity makes people with the syndrome more vulnerable to viruses and colds.
Methods for diagnosing chromosomal abnormalities
Chromosomal abnormalities can be diagnosed by non-invasive and invasive methods. The first allow you to establish a number of pathologies characteristic of chromosomal abnormalities. Invasive methods are used to make an accurate diagnosis.
ultrasound
Establishing the risk of Down syndrome in a fetus by ultrasound is called ultrasound screening. Often the method is used in combination with a biochemical analysis of the mother's blood. The accuracy of diagnosing Down syndrome on ultrasound in the second trimester of pregnancy can reach 91%. The examination is carried out at 11-13 and 16-18 weeks of pregnancy.
Invasive techniques
Invasive prenatal diagnosis can lead to a number of complications. The risk to the fetus and mother is small. However, the procedure is prescribed only if necessary, if Down's syndrome in the fetus is confirmed by ultrasound data and maternal blood tests.
Biochemical screening
The main task of screening is to identify risk groups in terms of having a child with serious illnesses, including those with chromosomal disorders. Biochemical screening is recommended for all women in the first and second trimesters of pregnancy.
Diagnostics in the first trimester of pregnancy
In the first trimester of pregnancy, Down syndrome can be diagnosed by ultrasound, due to the presence of a number of pathologies. These include an increased thickness of the nuchal space in the fetus, reduced, compared with the norm, the size of the cerebellum and frontal lobe, impaired bone formation, heart defects, absence of the nasal bone, etc.
It is important to remember that no single marker will be considered sufficient for a reliable diagnosis of Down syndrome - there is not enough ultrasound data for this. Therefore, having received the results of the examination, you do not need to be upset ahead of time - you need to consult a specialist.
What to do if the diagnosis is confirmed?
Examination can show pathology in the fetus. It is up to the parents to decide what to do next. If they are ready for responsibility, then, even if Down syndrome is confirmed by ultrasound and invasive research methods, parents can leave the child. Despite the peculiarities of development, he can live a long and happy life. In cases where there are too many pathologies, doctors may recommend terminating the pregnancy. However, even in this case, the decision will be made by the parents.
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Ultrasound diagnostics of Down syndrome and other chromosomal abnormalities
- Ultrasound of the fetus is the main method for diagnosing the likelihood of Down syndrome
- Basic ultrasound markers of Down syndrome
- Signs of Down syndrome with ultrasound in the second trimester of pregnancy
- How else can you determine the risk of having a baby with Down syndrome
Down's syndrome is a relatively common congenital pathology caused by the presence of an extra chromosome in 21 pairs. Down syndrome is also called trisomy on 21 pairs of chromosomes.
Of all the chromosomal abnormalities, this pathology is the most well-known for a wide range of people.
Down's syndrome is associated with many significant malformations. Such as, for example, congenital heart defects, duodenal atresia (a condition where part of the small intestine does not develop), an increased risk of developing acute leukemia (leukemia). About 50% of children with this condition are born with heart defects, the most common of which is a ventricular septal defect. Another disease that is often observed in such children is Hirschsprung's disease - an aganglionic area of the large intestine, leading to the development of intestinal obstruction.
Screening tests during pregnancy are used to assess the risk of having a baby with Down syndrome. These tests are painless and non-invasive (do not cause damage to the tissues of the pregnant woman and fetus), but do not accurately judge the presence or absence of congenital pathology. Nevertheless, their widespread use makes it possible to suspect risks and recommend invasive procedures.
Invasive diagnostic methods include interventions performed under ultrasound guidance - amniocentesis, chordocentesis and chorionic villus sampling.
Fetal ultrasound is the main way to diagnose the likelihood of Down syndrome
Fetal ultrasound to detect developmental abnormalities is called ultrasound screening. Most often, ultrasound screening is combined with biochemical blood tests of a pregnant woman, and such a study is called combined screening. Depending on the choice of criteria, the probability of detecting Down syndrome in the second trimester is 60-91%. The use of color Doppler technology for ultrasound screening makes it possible to detect defects in the fetal heart and increases the accuracy of diagnosis.
Major ultrasound markers of Down syndrome
Ultrasound markers are the ultrasound measurements most likely to be associated with a high chance of having Down syndrome in the fetus. None of these markers is specific, that is, inherent only in this pathology.
The following indicators are taken into account: the thickness of the collar space (75% of sensitivity), the absence of the nasal bone (58%), heart defects, short femurs and humeri, hyperechoic intestines, choroid plexus cysts, echogenic foci in the heart, signs of duodenal atresia . Of course, none of these markers is an absolute sign of a chromosomal abnormality.
Measuring the thickness of the nuchal space
The nuchal space (cervical fold) is the area between the folds of fetal tissues, which is transparent on ultrasound, located below the occiput in the area of neck formation. In children with chromosomal abnormalities, such as Down's syndrome or trisomy 18, fluid accumulates in this place. The measurement of this space is carried out from 11 to 14 weeks during the ultrasound of pregnancy in the first trimester. Measurements obtained at this time are the most significant for predicting the individual risk of developing fetal chromosomal abnormalities. The thickness of the collar space more than 3 mm is taken as an indicator of an increased likelihood of genetic defects in the fetus.
The increase in the collar space does not mean that the fetus necessarily has Down syndrome, but if we take into account the gestational age of the fetus on which measurements were taken, the age of the mother and biochemical screening indicators, the probability of a correct diagnosis becomes higher than 80%. Although nuchal thickness screening is one of the most important tests for detecting chromosomal abnormalities, there are biases. The error arises due to violations of the measurement technique. This applies not only to measurements of the collar space, but also to the nasal bone. There are errors due to the human factor. The correct measurement technique and the experience of the ultrasound specialist are very important.
Measurements of the pelvis and structures of the fetal brain
In fetuses with trisomy 21, ultrasound may show cerebellar hypoplasia (reduction in size) and a decrease in the frontal lobe. These facts are used to assess the likelihood of Down syndrome.
The combination of a shortened transverse size of the cerebellum and a decrease in the fronto-thalamic distance is of greater importance for the diagnosis of this chromosomal anomaly than measuring each distance of intracerebral structures separately.
In a fetus with Down's syndrome during ultrasound, the length of the iliac bones is clearly reduced and the angle between these bones is increased. This can be measured most clearly at the level of the middle of the sacrum in cross section.
Signs of Down's syndrome during ultrasound in the second trimester of pregnancy
When performing ultrasound of the fetus in the second trimester of pregnancy, such abnormalities can be detected as a violation of the formation of bones of the skeleton, expansion of the collar space by more than 5 mm, the presence of heart defects, expansion of the renal pelvis (pyeloectasia ), echogenicity of the intestine, cysts of the choroid plexus of the brain. Moreover, only heart defects, disorders of skeletal formation and expansion of the collar space are independent risk factors.
The use of only one of the measurements in assessing the probability of the presence of chromosomal abnormalities of the fetus, for example, determining the thickness of the collar space or measuring the iliac angle, is less accurate than taking into account the totality of measurements.
Another way to determine the risk of having a baby with Down syndrome
In addition to ultrasound signs, biochemical screening in the first and second trimester is used to determine the degree of risk. In this case, the blood of a pregnant woman is examined. The best results are obtained by combining ultrasonic and biochemical signs. If the combination of factors is threatening, a decision may be made to conduct invasive methods for diagnosing Down syndrome and other chromosomal abnormalities. Invasive techniques consist in obtaining particles of the skin or blood of the fetus, followed by genetic analysis. These methods are 100% reliable. At the same time, even complete well-being during screening in the first and second trimester using ultrasound and biochemical markers cannot guarantee the absence of chromosomal abnormalities in the fetus.
