What Is Sequential Screening Test: Why It Is Required And How It Works
Pregnancy is a precarious time when many tests must be conducted for the excellent health and development of the mother and the baby. These tests are not the common ones, and not everybody has to undergo them, and one of the criteria is “sequential screening.” This screening is an added test done for a diagnosis that is optional and suggested by the doctor. It is a test which most of the expectant mothers are not comfortable, but since it is crucial for the mother, we will highlight everything related to this test.
Going forward, we will be discussing what this test all about, the cost involved is, the reasons why it needs to be done, its duration, procedure, efficacy, etc.
What Is Sequential Screening?
This screening consists of a sequence of tests done in the prenatal stage like ultrasound and blood test for checking the defects in the neural tube and genetic aberrations. This test is done in two steps to assess the probability of the fetus with Down syndrome, anencephaly, Trisomy 18 Spina Bifida, etc.
The process of screening assimilates both the findings of the blood tests as well as the report of the ultrasound done in the first trimester comprising of the details regarding the mother and the baby. This test is not mandatory and can be opted if one wants. A medical practitioner helps in deciding if this test should be undertaken by the mother.
These tests cannot help in diagnosing a specific situation but helps in a comprehending with any threats which are there.
How Does Sequential Screening Test Work?
The screening process is carried in two-steps, the first being the ultrasound and the blood test that is carried within ten to fourteen weeks and another stage where a single blood test is performed at fifteen to twenty-one weeks.
1. Sequential Screening Stage One:
Ultrasound:
The accumulation of the fluid at the rear portion of the neck of the baby is referred to as NT. The ultrasounds also assist in assessing the fluid in the baby’s body. All babies who get diagnosed with trisomy 18, Down syndrome or other anomalies are disposed to an additional fluid as well as higher NT.
Apart from the NT magnitude, the ultrasound done during the first trimester helps in determining the baby’s development, gender, and gestational age.
Blood testing:
The placenta is known to produce proteins at the time of pregnancy, which can be transmitted to the mother’s blood as well. The babies who are diagnosed with any anomalies, Down syndrome, trisomy 18 will exhibit higher protein levels. The blood tests also help to assess the following threats as well.
The lower protein levels increase the chances of threats of trisomy 18 and down syndrome. It is related to other pregnancy threats comprising of high BP ratings, low weight at birth, miscarriage, etc. but all are not necessarily a sign of unhealthful pregnancy.
The increased levels of HCG are a sign of Down’s syndrome and trisomy 18. Different types of HCG screening are done for detecting protein levels.
2. Sequential Screening Stage Two:
Quad screen as it is also commonly known as comprises of the blood test that assists in calculating the Alpha-fetoprotein, dimeric inhibin, HCG free estriol.
The increased number of proteins that get transmitted to the mother’s blood is produced by the placenta, and all babies with anomalies show either a too high or too low level of proteins.
The typical proteins that can be calculated in stage two of the blood test are as follows:
AFP:
The liver of the baby produces a protein in the second half of the pregnancy, and its levels increase as the pregnancy advances. The levels are on the higher side in case the baby has any threats of a defect that happens when the spinal cord and the spine do not develop in the proper manner.
In case the baby has defects in the spine, brain or the spinal cord or called the ONTD, or a gap or a notch in the baby’s skin, it assists the AFP to disappear in the protective fluid which is in the amniotic bag that is cushiony for the baby when in the mother’s womb, and finally in the mother’s blood. Thus, increasing the AFP levels, whereas AFP levels are reduced if the baby has any risks of Edward’s syndrome.
HCG:
HCG protein is produced by the protein, but its levels start diminishing during the second trimester. While increased levels are related to Down Syndrome, declining levels are linked with trisomy 18.
Unconjugated estriol (UE3):
This protein is produced by both the liver and the placenta, and this stays at increased levels all through the pregnancy. Decreased levels in protein indicate the baby having chances of Edward’s Syndrome.
Dimeric inhibin A (DIA):
Placenta produces this protein, and this protein level lies steady among the 15th as well as the 18th week. The increased protein levels are connected with Trisomy 21 while the decreased levels with Edward’s Syndrome.
How Accurate Is the Sequential Screening Test?
How Accurate Is the Sequential Screening Test
The sequential screening test cannot reveal any genetic anomalies. The decisiveness is dependent on the individual’s skills and the test results as well. This screening, on the other hand, helps to find the following:
- 90% of the infants with Down syndrome
- 80% of the newborn with trisomy 18
- 80% of the newborn baby with Spina bifida
Trisomy 21, also referred to as Down syndrome, is produced by an additional chromosome and one in about 600-900 babies are born with it. It also causes cardiovascular disease and mental disorders amongst all. The possibility of Down syndrome in a baby multiplies with the age of the mother.
The growing baby has an additional chromosome that leads to Trisomy 18. One in 6000-8000 babies is born with it. It can lead to mental retardation, cardiovascular disease, weak growth, etc. Alike Trisomy 21, the possibility of Edward’s syndrome also increases with the age of the mother.
ONTD or Open neural tube defects takes place if the spine is not formed appropriately, which exposing and damaging the spinal cord. One out of 1,000 infants have the chances to foster these anomalies.
The results of this test are an indication to show the baby having genetic anomalies, but other tests are recommended as well.
How Much Time Do the Results Take?
The results of the sequential screening can be expected in a week’s or less after submitting the samples of the blood.
Sequential Screening Test Results:
The very first round of the ultrasound assesses the levels of NT. In case they are too high, the doctor will recommend more test. To evaluate the cell-free fetal DNA (cff DNA), chorionic villus sampling, a part of the tissue sample from the placenta is taken. In case the NT or the nuchal translucency fluid is not normal, there are more chances of the baby to be detected with chromosome related anomalies.
What to Do If Sequential Screening Shows High Risk or Abnormal Results?
In a case where the sequential screening shows high risks or not typical results, the doctor will most probably refer the mother to a specialist who deals with cases of high risks in pregnancy like a perinatologist, maternal medicine fetal specialist, etc. These specific doctors can thus recommend additional tests or even refer to other counsellors who can describe the detailed results, resolving all queries and taking the ideal decision.
Advanced testing options comprise of prenatal screening. An ultrasound will be performed. Amniocentesis, as well as a test that helps to assess if the lady has higher chances of having a baby with trisomy 21, will also be performed (all of them not compulsory though).
What to Do If Sequential Screening Shows Low Risk or Normal Results?
In case the screening results of stage one is on the normal side, the doctor will ask for a revert at 15-22 weeks for screening at stage 2, and the findings at this stage will further help in assessing the trisomy 18, down syndrome and other anomalies. In case, the results are not abnormal and negative, and the baby has fewer chances to have genetic defects. The medical practitioner will persist in keeping monitoring the baby all through the prenatal checks.
Are Sequential Screening Procedures Standard for All Pregnant Women?
Sequential screening tests are recommended to all the expectant women, yet more importantly, to those who have a high risk in pregnancy. Sequential screening tests are conducted for women who are:
- Above 35 years in age
- Those who have had congenital disabilities in the family history
- Those who underwent radiation treatments
- Those who contracted diabetes
- Those who had massive exposure to medicines.
Does Sequential Screening Also Work Accurately for Twins?
Twin detection is also done by sequential screening; however, the evaluation is a tricky one, and its accurateness is lower as well. Distinct laboratories have several approaches to this screening. Few medical experts separately evaluate every fetus while others assess them as a unit in whole. The doctor can throw more light with details related to the screening.
Thus, sequential screening helps to figure the risk that the baby has concerning anomalies in chromosomes and offer the next due step. It is even essential to let a genetic/ medical practitioner analyze the results for better clarity and vision.
Source: https://www.beingtheparent.com/what-is-sequential-screening-test-why-it-is-required-and-how-it-works/
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