What is Aneuploidy Screening?
Types of Aneuploidy Screening
Interpreting Aneuploidy Screening Results
When Should One Consider Aneuploidy Screening?
Conclusion
Early pregnancy comes with lots of excitement and expectations. One such expectation is that the baby grows healthy and the pregnancy progresses smoothly. However, sometimes, due to genetic conditions, pregnancy complications, or chromosomal abnormalities, concerns arise. At this stage prenatal care, particularly aneuploidy screening, plays a major role. Aneuploidy screening helps to detect potential chromosomal abnormalities early on, allowing parents, and the Obstetrician, and Fetal Medicine Specialist to make informed decisions and prepare for any challenges that may arise during the pregnancy.
What is Aneuploidy Screening?
Aneuploidy refers to the occurrence of one or more extra chromosomes or missing chromosomes in a cell. In general, our human body consists of 46 chromosomes, arranged in 23 pairs. Aneuploidy occurs when this number is deviated. Aneuploidy screening helps detect these conditions early in the pregnancy. This abnormality in chromosomes greatly impacts a child’s development and health. It often leads to conditions like Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), or Patau syndrome (Trisomy 13).
Types of Aneuploidy Screening
This screening can be carried out in different stages of pregnancy using various methods. These methods serve as an indication or likelihood of an abnormality. All the methods incorporated have their limitations, pros, and accuracy.
First-Trimester Screening
First-trimester screening is a prenatal test that involves ultrasounds and blood tests to detect fetal aneuploidies. This screening has a 95% detection rate with a 3% false positive rate. Some screening that comes under this trimester is:
Nuchal Translucency (NT) Ultrasound:
This ultrasound measures the amount of fluid behind the baby’s neck. With the amount received, the chances of having a chromosomal or genetic variant are determined. The high amount of fluid indicates a higher risk of aneuploidy, particularly Down syndrome while a small amount is considered normal.
Blood Tests:
Blood tests measure specific proteins and hormones in the mother's blood, such as hCG (human chorionic gonadotropin) and PAPP-A (pregnancy-associated plasma protein A). Abnormal levels can suggest a higher risk of chromosomal abnormalities.
Non-Invasive Prenatal Testing (NIPT)
NIPT is a highly accurate screening method that analyzes small fragments of fetal DNA circulating in the mother's blood. It is usually performed around 10 weeks of pregnancy and can detect common aneuploidies like Trisomy 21, 18, and 13 with over 99% accuracy. NIPT has a lower false-positive rate compared to other screening methods.
Second-Trimester Screening- Quadruple Marker Test (Quad Screen):
This blood test is typically done between the 15th and 20th weeks of pregnancy. It measures four substances in the mother's blood: alpha-fetoprotein (AFP), hCG, estriol, and inhibin-A. This test can detect an increased or low risk of aneuploidy or neural tube defects.
Combined Screening
A combination of first-trimester screening and NIP or second-trimester screening to increase the accuracy of risk assessment. Combined screening provides a way more comprehensive evaluation of the risk of chromosomal abnormalities.
Interpreting Aneuploidy Screening Results
It’s important to note that screening tests are not diagnostic tests but rather they do assess the risk of chromosomal abnormality. Screening test indicates two different results:
Low-Risk Results:
High-Risk Results:
A low-risk result suggests that the likelihood of a chromosomal abnormality is low, but it does not eliminate the possibility.
A high-risk result indicates a higher chance of aneuploidy, in which the health care provider may offer further diagnostic testing to fully detect the aneuploidy.
When Should One Consider Aneuploidy Screening?
Aneuploidy Screening is offered to all pregnant women, as a part of their routine checkups and prenatal care. However, in certain situations, this test is recommended with greater emphasis:
Maternal Age:
Family History:
Previous Pregnancy with Chromosomal Abnormalities:
Abnormal Ultrasound Findings:
Increased Risk Identified by First-Trimester Screening:
Women who are 35 years or older at the time of delivery are at a higher risk of chromosomal abnormalities, making aneuploidy screening important.
If there is a family history of chromosomal abnormalities or genetic disorders, this screening can help assess the risk for the current pregnancy.
Women who have had a previous pregnancy affected by a chromosomal abnormality may choose to undergo aneuploidy screening in subsequent pregnancies.
If an ultrasound shows abnormalities that could indicate a chromosomal issue, aneuploidy screening can help further evaluate the risk.
If early screening tests indicate an increased risk of chromosomal abnormalities, further aneuploidy screening or diagnostic testing may be recommended.
Aneuploidy screening is generally performed during the first or second trimester of pregnancy, allowing for early detection and better decision-making. Discussing with your fetal specialist can help determine the best time for screening based on individual risk factors and preferences.
Conclusion
Aneuploidy screening is a great medical invention in the field of prenatal care, that offers an early insight into the health of a fetus. Although the results of screenings are just the likelihood but do provide an early indication to the parents as well as the doctor to make informed and wise decisions.
If you are expecting or planning a pregnancy, discuss aneuploidy screening with the leading fetal medicine specialist Dr. Mansi Gupta. Book an appointment now to explore and understand more options and ensure a healthy pregnancy and baby.
