Is Mid-Pregnancy Quad Screen Necessary After First Trimester Testing?

The Four Indicators of Middle Tang Dynasty

Hello, doctor: If the initial screening for the nuchal translucency (NT) test is normal, is it still necessary to perform the second-trimester quadruple marker screening? Would doing both tests increase the risk of false positives? Thank you for your response.

GIGI, 20~29 year old female. Ask Date: 2012/09/12

Dr. Liu Yuhong reply Obstetrics and Gynecology

In the early Tang (nuchal translucency) and mid-Tang four marker tests, both have similar efficacy in detecting Down syndrome, identifying approximately 80% of Down syndrome babies, but there is a 5% false positive rate.
"If both tests are performed, does it increase the false positive rate?" Mathematically, it is inevitable that the false positive rate will increase if the test results are reported separately for early and mid-pregnancy (two sets of probability values).
Unless the data from both blood tests, along with nuchal translucency measurements and maternal age, are combined to form what is known as "integrated screening for Down syndrome." Integrated screening for Down syndrome can similarly detect about 80% of Down syndrome babies but has only a 0.5% false positive rate.
For more information on integrated screening for Down syndrome, please refer to http://www.cpmc.org/learning/documents/intscreen-chin.pdf.

Reply Date: 2012/09/12

More Info

The necessity of conducting a Mid-Pregnancy Quad Screen after passing the First Trimester Screening, such as the nuchal translucency test, is a common concern among expectant mothers. To address your question, let's first understand the purpose and implications of these tests.

The First Trimester Screening typically includes a blood test and an ultrasound to measure the nuchal translucency (NT) of the fetus. This screening is primarily aimed at assessing the risk of chromosomal abnormalities, particularly Down syndrome (trisomy 21) and trisomy 18. If the results indicate a low risk, many women feel reassured. However, it is important to note that no screening test is definitive; they only provide risk assessments.

The Mid-Pregnancy Quad Screen, usually performed between 15 and 20 weeks of gestation, measures four specific markers in the mother’s blood: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), estriol, and inhibin A. This test is designed to further assess the risk of Down syndrome, trisomy 18, and neural tube defects.
Now, regarding your concern about whether it is necessary to undergo the Quad Screen after a successful First Trimester Screening:
1. Complementary Nature of Tests: The First Trimester Screening and the Quad Screen are complementary. While the first test focuses on early markers and provides an initial risk assessment, the Quad Screen offers additional information that can help refine the risk profile as the pregnancy progresses. It is not uncommon for women to have both tests to ensure a comprehensive evaluation.

2. Risk of False Positives: You mentioned the concern about increasing the likelihood of false positives by undergoing both tests. While it is true that each screening has its own false positive rate, the information gained from both tests can be invaluable. If both tests indicate a low risk, it can provide greater reassurance. Conversely, if either test indicates a higher risk, it may prompt further diagnostic testing, such as amniocentesis or chorionic villus sampling (CVS), which can provide definitive answers.

3. Clinical Guidelines: Many healthcare providers recommend the Quad Screen even if the First Trimester Screening results are reassuring. This is particularly true for women who are at higher risk due to factors such as advanced maternal age, family history of genetic disorders, or other risk factors.

4. Informed Decision-Making: Ultimately, the decision to proceed with the Quad Screen should be made in consultation with your healthcare provider. They can help you weigh the benefits and risks based on your individual circumstances, including your medical history and any specific concerns you may have.

In summary, while the First Trimester Screening provides valuable information, the Mid-Pregnancy Quad Screen can offer additional insights that may be beneficial for your pregnancy management. It is essential to have an open discussion with your healthcare provider to determine the best course of action for your specific situation. Remember, the goal of these screenings is to ensure the health and well-being of both you and your baby, and having comprehensive information can aid in making informed decisions throughout your pregnancy.

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