Screening for Fetal Abnormalities: Down Syndrome and Spina Bifida

A pregnancy, there are several options available for identifying fetal abnormalities. Thanks to the advancements in modern medical technologies, expectant mothers have access to increasingly accurate screening tests that help in recognizing potential issues. The range of screening methods is expanding, thus reducing the number of necessary invasive procedures, such as amniocentesis, which is becoming less frequently required.

Importance of Fetal Abnormality Screening

Screening for fetal abnormalities is particularly important, as early diagnosis allows parents to make informed decisions regarding the continuation of their pregnancy. The most common chromosomal abnormalities, such as Down syndrome and spina bifida, can be screened using various methods. These tests are generally conducted during the first and second trimesters of pregnancy, allowing for appropriate professional intervention when necessary.

The screenings performed during pregnancy not only assist in the health of the fetus but also support the mental well-being of the mother, as parents can prepare for any potential challenges.

What is Down Syndrome?

Down syndrome occurs due to an anomaly of the 21st chromosome, which represents an excess of genetic information; instead of the normal two, there are three 21st chromosomes in the cells. Without any screening, about 1 in 600-700 infants is affected by this disorder, indicating that the risk is relatively low but not negligible.

This chromosomal abnormality is generally not inherited, so the fetus can carry this genetic defect regardless of family history. Various methods are available for screening Down syndrome during pregnancy, including maternal blood tests that determine levels of alpha-fetoprotein (AFP) and human chorionic gonadotropin (hCG).

As maternal age increases, the risk of Down syndrome also rises. In Hungary, it is common for chromosome testing to be recommended for mothers aged 35 and older, which may increase the risk of miscarriage by 1%. Since this test is generally not performed on younger mothers, most children with Down syndrome are born to younger mothers.

Down syndrome can cause not only intellectual disabilities but also various physical problems, such as heart diseases and sensory disorders. During risk assessment tests, trisomy of chromosomes 13 and 18 is also screened, although these abnormalities occur less frequently.

Spina Bifida

Spina bifida, one of the most severe congenital disorders, affects approximately 1 in every 400 children without screening tests, but the risk of its occurrence can be significantly reduced by taking prenatal vitamins.

Spina bifida involves developmental defects of the spine and central nervous system. Due to failures in the closure of the spinal column, injuries to the spinal cord can occur, leading to paralysis and weakness in the lower limbs. In some cases, the accumulation of cerebrospinal fluid may also occur, leading to hydrocephalus, which, although treatable with surgery, can often cause intellectual disabilities.

In some forms of spina bifida, the spinal cord is covered by a stronger layer of tissue, which is referred to as closed spina bifida. This type is not indicated by maternal blood tests, but genetic ultrasound performed between the 18th and 20th weeks can almost certainly detect it.

Thanks to the wide range of screening methods available, tests accessible to expectant mothers help in the early detection of abnormalities. The combination of ultrasound and blood tests allows for the planning of necessary interventions, which can contribute to the preservation of the fetus’s health.

Types of Prenatal Screenings

Various screening tests available during pregnancy assist in the early identification of fetal abnormalities. The Combined Test, conducted during the first trimester, between the 12th and 14th weeks, utilizes ultrasound and blood tests. Ultrasound is used to determine gestational age, measure the nuchal translucency, and check for the presence of the nasal bone.

In the second trimester, during the 16th to 19th weeks, the Integrated Test measures additional markers, such as AFP, uE3, and Inhibin-A. The Quad Test also takes place in the second trimester, where the aforementioned markers are analyzed.

These tests not only help assess the risk of Down syndrome but also enable the identification of spina bifida and other chromosomal abnormalities. Markers measured in maternal blood, such as PAPP-A and free-ß-hCG, change as the pregnancy progresses, so various factors must be considered for appropriate evaluation.

The sensitivity and reliability of these tests are continuously improving, allowing expectant mothers to diagnose potential abnormalities with as few invasive procedures as possible, such as amniocentesis. Therefore, performing the appropriate screening tests is crucial in protecting fetal health.