As an expectant parent, you may be concerned about the health of your unborn child and want to obtain as much information as possible during the course of your pregnancy. Perhaps the pregnancy has been classified as a "high-risk pregnancy," your NHS doctor detected some abnormalities during routine prenatal care, or further tests are recommended based on your family history. Whatever the reason, you may be considering additional prenatal tests to get more information.
Prenatal diagnostics refer to examinations that provide information about certain diseases, chromosomal and genetic conditions, and disabilities of the unborn child. There are non-invasive and invasive examination methods, which we will introduce in this article.
Non-Invasive Tests
Non-invasive examinations do not interfere with the woman's body and therefore do not pose a risk to the unborn child. However, it should be noted that non-invasive tests do not deliver a diagnosis but rather a probability of a condition expressed in numbers (e.g., 1:250). The only way to get a diagnosis is via an invasive test (see below).
Ultrasounds
In the UK, you will typically be offered at least two ultrasounds during your pregnancy: the dating scan around weeks 11-14 and the anomaly scan around weeks 18-21. Additional scans may be recommended based on your individual needs.
Special ultrasound examinations include:
- Doppler ultrasound: Checks blood flow to the uterus and placenta, umbilical cord, and important vessels of the child.
- Echocardiography: Detailed examination of the fetal heart, including heart valves and blood flow.
- 3D ultrasound: Combines many individual ultrasound slice images to form a three-dimensional image.
- 4D ultrasound: Displays a three-dimensional image of the baby in real-time, making baby movements instantly visible.
Nuchal Translucency Scan
During a special ultrasound examination in pregnancy week 12-14, the nuchal translucency (accumulation of fluid in the area of the child's neck) is measured. This scan can indicate chromosomal conditions and abnormal development if the fluid increases in size. The main conditions assessed include Trisomy 21 (Down syndrome), Trisomy 13 (Patau syndrome), and Trisomy 18 (Edwards syndrome). This test, known as the nuchal fold scan, costs between £25 and £150, although some NHS Trusts may cover the cost for high-risk pregnancies.
First Trimester Screening
The nuchal translucency scan is often combined with a blood test as part of the First Trimester Screening. The maternal blood values, maternal age, and nuchal translucency values are correlated to provide a risk assessment for chromosomal abnormalities. This test typically costs around £100-170, if you choose to do it privately, but is covered by the NHS as part of their screening program.
Many expectant parents opt for the NIPT test in London at specialized clinics like the London Pregnancy Clinic, which offers comprehensive prenatal care and advanced screening options.
Molecular Genetic Blood Tests / Non-Invasive Prenatal Tests (NIPT)
In molecular genetic blood tests, blood is taken from the pregnant woman, and the DNA of the unborn child is analyzed for certain chromosomal characteristics. This test can detect trisomy 21, 18, and 13 with a high degree of certainty and can be conducted from the 10th week of pregnancy. As of July 2022, the test may be covered by the NHS for women with an abnormal first trimester screening result or if deemed necessary by the doctor. Otherwise, the test costs around £100-250.
Invasive Prenatal Tests
Invasive prenatal examinations involve taking tissue samples of the developing placenta, amniotic fluid, or fetal blood. Unlike non-invasive screenings, these tests can confirm or diagnose the presence of a trisomy or other genetic conditions.
Chorionic Villus Sampling
Fetal cells are taken from the developing placenta through the abdominal wall with a thin needle to search for chromosomal abnormalities and hereditary diseases. This test is performed around the 12th-13th week of pregnancy and carries a miscarriage risk of about 0.5-1%.
Amniocentesis (Amniotic Fluid Test)
For this test, 8-10ml of amniotic fluid containing cells of the child are taken through the abdominal wall with a thin needle. The cells are examined for chromosomal abnormalities, and the value of alpha-1-fetoprotein is determined. This test is usually performed in the 15th-18th week of pregnancy and has a miscarriage risk of 0.2-1%.
Umbilical Cord Puncture (Chordocentesis, Fetal Blood Sampling)
In special situations, fetal blood is taken from the umbilical cord to examine for hereditary diseases, blood diseases, or infectious diseases. This procedure is performed from the 18th week of pregnancy and carries a complication risk of 1-3%, decreasing with increasing duration of pregnancy.
The Role of Non-Invasive Prenatal Testing (NIPT)
Since its debut in 2011, NIPT has demonstrated its effectiveness in detecting a growing number of diseases, offering a less invasive approach to prenatal chromosomal disease screening. However, its normalization can lead to over-screening, exacerbating pregnancy-related anxiety. NIPT is a screening tool and not a diagnostic one, requiring confirmatory invasive methods if a positive result is obtained.
NIPT involves bioinformatics analysis on a cell-free DNA (cfDNA) sample extracted from the mother’s placenta to determine the fetal fraction (FF), crucial for quality control and statistical confidence in the results. Raising clinician awareness about FF's significance enhances patient care and alleviates concerns about failed NIPT.
Deciding Whether to Test
Determining whether to undergo prenatal tests can be challenging. Factors like personal and family history, NHS midwife or consultant recommendations, and pregnancy classification play a significant role.
0 Comments