How useful is Quadruple marker fetus in a pregnant woman at 16-18 week of pregancy

The quad screen — also known as the quadruple marker test, the second trimester screen or simply the quad test — is a prenatal test that measures levels of four substances in pregnant women's blood:

·         Alpha-fetoprotein (AFP), a protein made by the developing baby

·         Human chorionic gonadotropin (HCG), a hormone made by the placenta

·         Estriol, a hormone made by the placenta and the baby's liver

·         Inhibin A, another hormone made by the placenta

Ideally, the quad screen is done between weeks 15 and 18 of pregnancy — during the second trimester. However, the procedure can be done up to week 22.The results are put in a software and results are expressed in terms of probability 

The quad screen is used to evaluate whether the indexed pregnancy has an increased chance of being affected with certain conditions, such as Down syndrome or neural tube defects. If risk is low, the quad screen can offer reassurance that there is a decreased chance for Down syndrome, trisomy 18, neural tube defects and abdominal wall defects.

If the quad screen indicates an increased chance of one of these conditions, you might consider additional screening or testing.

Why it's done

The quad screen evaluates  chance of carrying a foetus who has any of the following conditions:

·         Down syndrome (trisomy 21). Down syndrome is a chromosomal disorder that causes lifelong intellectual disability and developmental delays and, in some people, health problems.

·         Trisomy 18. This is a chromosomal disorder that causes severe developmental delays and abnormalities in the structure of the body. Trisomy 18 is often fatal by age 1.

·         Spina bifida. Spina bifida is a birth defect that occurs when a portion of the neural tube fails to develop or close properly, causing defects in the spinal cord and in the bones of the spine.

·         Abdominal wall defects. In these birth defects, the baby's intestines or other abdominal organs stick through the belly button.

The quad screen has traditionally been one of the most commonly used screenings in the second trimester. It was generally used if prenatal care began during the second trimester or if first trimester screening, which involves a blood test and an ultrasound exam, wasn't available. Physician might combine the results of first trimester screening with the quad screen to improve the detection rate of Down syndrome.

Prenatal cell-free DNA screening is another screening method that  doctor  might recommend in place of quad screening.

A negative quad screen doesn't guarantee that the baby won't have a) chromosomal abnormality, B) single-gene disorder or C) certain birth defects. If screening test is positive,  physician will  recommend additional testing to make a diagnosis.

Caveat :-What we achieve by all these 5 test 1) Cell Free Foetal DNA (cffDNA) 2) D marker  3) NT Scan 4) Quadruple marker 5) TIFA ,Before the commencement  of screening, doctor  should counsel the couple about what the results mean to her . Doctor should also consider whether the screening will be worth any anxiety it might cause, or whether doctor will handle her  differently depending on the results. The concerned woman must be made aware for sell confirmation of chromosomal abnormalities an invasive test is essential  might also consider what level of risk would be enough for you to choose a more invasive follow-up test.

The quad screen is a routine prenatal screening test. The test poses no risk of miscarriage or other pregnancy complications. As with other prenatal screening tests, however, the quad screen can cause anxiety about the possible test results and what they might mean for her foetus. How to counsel??  Before the test, health care provider might ask the couple to meet with a genetic counselor in cases of more than few pregancy losses Or your health care provider might provide genetic counseling during your routine prenatal care appointment.

Results

The quad screen measures levels of alpha-fetoprotein (AFP), human chorionic gonadotropin (HCG), estriol and inhibin A in pregnant women's blood. Benefits this Q serum tests will strengthen the suspicion of certain A) chromosomal conditions, B) neural tube defects or C) abdominal wall defects.

Quad screen results give the level of risk of carrying a foetus who has certain conditions compared with the general population's risk. We and ANC women in general should keep in mind that a positive quad screen simply means that levels of some or all of the substances measured in her blood were outside the normal range.

Quad scan,  like Double marker serum markers has also statistical evaluation range and Apps (applications) so that possibility of chromosomal markers are calculated.   What are the factors that can affect the substances measured by a quad screen include:

·         A miscalculation of how long she  been pregnant

·         Maternal race

·         Maternal weight

·         Carrying more than one baby during a pregnancy

·         Diabetes

·         In vitro fertilization

·         Smoking during pregnancy

Some centers performs USG with take additional charges to have accurate gest age and no of fetuses she has inside so that exact probability can be established with near accurate, If her test results are positive, doctor  might compare previous screening reports like D marker(11-13.6 weeks) & NT scan reports and finally may opt for amniocentesis . The quad screen correctly identifies about 80 percent of women who are carrying a foetus who has Down syndrome. About 5 percent of women have a false-positive result.

Limitations of all screening tests:--When one  consider that his pts test results are abnormal ( remember that the quad screen only indicates her overall chance of carrying a foetus) who has certain chromosomal conditions, neural tube defects or abdominal wall defects. A decreased chance (negative screen result) doesn't guarantee that her foetus won't have one of these conditions. Likewise, an increased chance (positive screen result) doesn't guarantee that her foetus  will be born with one of these conditions.

Often, positive screen results might cause one to consider other testing, such as:

·   Prenatal cell-free DNA screening. This sophisticated blood test examines cell-free DNA from the placenta and the fetus in the mother's bloodstream. It evaluates whether her foetus is at risk of Down syndrome, extra sequences of chromosome 13 (trisomy 13), extra sequences of chromosome 18 (trisomy 18) or a sex chromosome abnormality, such as Turner syndrome. A normal result might eliminate the need for an invasive prenatal diagnostic test.

·   Targeted ultrasound. If there is  high risk of a neural tube defect, doctor  might suggest this test but by and large this TIFA (anomaly scan) has now become universal but ultrasound isn't an effective screening tool for Down syndrome.

·   Chorionic villus sampling (CVS). This procedure can be used to diagnose chromosomal conditions, such as Down syndrome. During CVS, a sample of tissue from the placenta is removed for testing. CVS poses a slight risk of miscarriage and isn't useful in detecting neural tube defects, such as spina bifida.

·   Amniocentesis. Amniocentesis can be used to diagnose both chromosomal conditions and neural tube defects. During amniocentesis, a sample of amniotic fluid is removed from the uterus for testing. Like CVS, amniocentesis poses a slight risk of miscarriage.

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