Triple Screening In Pregnancy - Essential Elements, Process And Accuracy

Triple Test In Pregnancy

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One of the biggest fears for a pregnant woman is the risk of her baby having abnormalities such as Down Syndrome, Edwards Syndrome or nueral tube defects. The fear is understandable, as the anamolies can have a dibilitating effect on the child. With technology advancing at a pace like never before, it is now possible to find out the defects in the baby in the womb itself through the triple screening test.

What Is The Triple Screen Test?

A triple screen test, also called the kettering test or triple screen or the Bart’s test, is a blood screening test that checks alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), (1) and estriol.

  • AFP: Fetus produces the AFP protein.
  • hCG: The hormone is produced in the placenta.
  • Estriol: Both the placenta and the fetus produce estrogen called estriol.

All the three leave their traces in the mother’s bloodstream. The test helps doctors analyze the possibility of birth defects in the baby.

[ Read: Alpha Fetoprotein Test During Pregnancy ]

Need For A Triple Screening Test In Pregnancy:

Going for a triple screening test in the second trimester of pregnancy would help you get a clue of possible abnormality in the fetus. The test is highly recommended for women who:

  • have a family history of birth defects.
  • are aged 35 years or more.
  • consumed harmful drugs or medications during pregnancy.
  • are exposed to high radiation levels.
  • are diabetic and using insulin.
  • are affected with viral infection during pregnancy.

When And How Is Triple Test Performed?

The triple screen test is performed between 15th and 20th week. The simple test involves drawing blood samples from you and testing them in a laboratory. The results are usually out within a few days.

What Are Analyzed In The Triple Screen Test In Pregnancy?

Triple screening test in pregnancy analyzes AFP levels, besides abnormal levels of hCG and estriol.

  • High AFP (also known as Maternal Serum AFP, or MSAFP) levels indicate spina bifida or anencephaly, a neural tube defect in growing baby.
  • Low AFP levels and abnormal hCG and estriol levels indicate Down Syndrome (Trisomy 21) (2), Edwards Syndrome (Trisomy 18) (3) or other chromosomal abnormalities.
  • The test also helps in identifying multiple pregnancy as well as the advancement of pregnancy.
AFPUE3hCGAssociated conditions
lowlowhighDown Syndrome
lowlowlowtrisomy 18
highn/an/aneural tube defects (like spina bifida), multiple gestation (like twins or triplets), or an underestimation of gestational age.

Source

While analyzing the results, the risk is calculated after considering the following:

  • The age of the expectant mother.
  • If the mother is carrying more than one fetus. Multiple fetuses increase the levels of MSAFP because each fetus secretes its own AFP .
  • If she is diabetic because those dependent on insulin have 20% lower levels of MSAFP than normal women.
  • Gestational age of the baby. Incorrect calculation of gestation is a common cause for showing abnormal MSAFP levels.
  • Weight of the mother, as the MSAFP level decreases with the increase in the maternal weight.
  • Ethinicity is also considered before concluding on the triple screen test results. For example: African-American women have 10-15% higher MSAFP than Caucasian women.

[ Read: Sequential Screening During Pregnancy ]

How Accurate Is Triple Test In Pregnancy?

  • Triple test is considered to be most accurate when performed between the 16th and 18th week of pregnancy. It has a 70% sensitivity and 5% false-positive rate.
  • The accuracy of a screening test is based on the number of times it correctly identified birth defects.
  • In 80 out of 100 fetuses, the triple and quad tests rightly found tube defects like spina bifida.
  • The tests correctly found anencephaly in 90 out of 100 fetuses.
  • In 69 out of 100 fetuses, the triple tests successfully detected down syndrome.
  • In 81 out of 100 fetuses, the quad tests successfully found down syndrome. (4)

What Do Results Of Triple Screen Test Indicate?

Screening tests do not diagnose a problem but signal the requirement for further tests. Same is the case with triple screen test, which is not diagnostic. The test only indicates the probability of a mother carrying a baby with a genetic disorder.

The results of the triple screening are usually available in one or two weeks. A positive result means that there is an increased risk of chromosomal and neural tube defects. In such cases, the expectant mother is made to undergo diagnostic tests.

Further Testing To Diagnose Abnormalities:

Additional testing is required when triple screen results show something abnormal. As a conservative method, a second triple screen is usually performed, followed by a high definition ultrasound. The ultrasound test can check the age of the baby, its spinal cord, kidneys, heart, and brain for any defects.

An invasive procedure called amniocentesis (5) may be performed if the abnormal results repeat. It helps in checking the baby’s chromosomes and tracking the problems, if any. Performing further tests could diagnose the issue and help consider an option that is good for both the unborn baby and mother.

[ Read: Amniocentesis Test ]

Are There Any Risks Associated With Triple Test?

The non-invasive blood test procedure has little risk to both mother and the fetus. There could be some discomfort while drawing blood but no side effects are linked to triple screening test in pregnancy.

Variations Of Screen Tests:

Sometimes, the term ‘multiple-marker screening test’ is used instead of triple screening test. This includes double test and quadruple test.

1. Double Test:

Double marker test is a blood test where free beta hCG and PAPP-A (pregnancy associated plasma protein) markers are checked in the blood.

High level of Free Beta hCG indicates risk of Down Syndrome and low level Trisomy 18 and 21.

Low level of PAPP-A indicates risk of Down Syndrome and Trisomy 18 and 21.

Double marker test is done between 10-13 weeks of pregnancy. A double test is considered obsolete in the UK.

[ Read: Fetal Echocardiography ]

2. Quadruple Test:

It is also called quad test or quad screen or tetra screen. While the triple screen measures the levels of AFP, hCG and estriol in your blood, quad screen additionally tests for a hormone called ‘Inhibin A’, which is made by placenta. The quad screen is performed between 14 and 22 weeks.

When taken between 15 and 18 weeks of gestational age, the quad screen has 81% sensitivity and 5% false-positive rate for detecting Down syndrome.

InhibinAAssociated conditions
HighTrisomy 21Down Syndrome
LowTrisomy 18(Edward s syndrome)
VariableTrisomy 13(Patau syndrome)

How was your experience with triple screen during your pregnancy? Share your thoughts on the process and results with us.

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