Second Trimester Screening Tests: The Difference Between Common Pregnancy Blood Tests and Genetic Testing

There is an array of tests conducted during the second trimester of pregnancy, which lasts from week 13 to 28. Blood tests at this timeframe play a pivotal role in providing insights into various aspects of maternal and fetal health. Common pregnancy blood tests and genetic screenings are very different tools that serve distinct purposes in prenatal care.

Common pregnancy blood tests, such as the complete blood count (CBC), blood typing, and tests to assess glucose levels, thyroid function, and infectious diseases, are routine components of prenatal care. These tests primarily focus on monitoring the mother’s overall health and identifying any conditions that may impact the course of the pregnancy. In contrast, genetic screening delves into the realm of the fetus’s genetic makeup, aiming to identify potential chromosomal abnormalities or genetic disorders. Knowing and understanding what these pregnancy tests are looking for, can help alleviate the stress many expectant parents feel about prenatal testing.

What common problems can be detected through prenatal blood testing and genetic screening?

Prenatal blood testing is a common aspect of prenatal care, and it can provide valuable information about the health of both the mother and the developing fetus. Some common problems that can be detected through prenatal blood screening include:

Down syndrome (Trisomy 21): Prenatal blood tests, such as non-invasive prenatal testing (NIPT) or the first trimester screening, can identify an increased risk of Down syndrome by analyzing the levels of specific proteins and hormones in the mother’s blood. The combination test combines a blood test measuring specific proteins and hormones with an ultrasound to assess the thickness of the nuchal translucency (the space at the back of the baby’s neck). Abnormal results may indicate an increased risk of Down syndrome.  NIPT, on the other hand, is a blood test that analyzes cell-free DNA from the placenta circulating in the mother’s bloodstream. It can detect the presence of extra chromosomes, including the one associated with Down syndrome. NIPT is highly accurate and is typically offered to women at higher risk, such as those over 35 or with other risk factors. These tests are typically performed during the early part of the second trimester.

Edwards syndrome (Trisomy 18) and Patau syndrome (Trisomy 13): These conditions can also be detected through certain prenatal blood tests during the second trimester that check for the presence of an extra copy of chromosome 18 and 13. In addition to the Combination Test and NIPT testing, a Quad screen may be employed to measure the levels of certain proteins and hormones in the mother’s blood. Abnormal levels may indicate an increased risk of chromosomal abnormalities. As with Down Syndrome final verification of these genetic abnormalities are typically confirmed through amniocentesis or chorionic villlus sampling.

Neural Tube Defects: Some blood tests can screen for neural tube defects like Spina bifida and anencephal by measuring the levels of alpha-fetoprotein (AFP) in the mother’s blood.

Rh incompatibility: Blood tests are conducted to determine the mother’s blood type and Rh factor. The Rh factor is a protein found on the surface of red blood cells, and individuals are classified as Rh-positive or Rh-negative based on the presence or absence of this factor. Rh incompatibility can lead to complications in future pregnancies, and measures can be taken to prevent issues such as hemolytic disease of the newborn. This test is typically performed very early in the pregnancy during the first or second trimester.

TORCH infections (Toxoplasmosis, Rubella, Cytomegalovirus, and Herpes): These infections can have serious consequences for the developing fetus. Blood tests may be used to check for antibodies indicating exposure to these infections.

Carrier Screening for Genetic Disorders:
Carrier screening for genetic disorders in pregnancy is a process that involves testing individuals to determine whether they carry a gene mutation associated with certain genetic conditions. This type of screening is often recommended for individuals or couples who have a family history of specific genetic disorders or belong to ethnic or racial groups with a higher prevalence of certain conditions. Ideally, carrier screening is performed before conception, allowing individuals or couples to assess their risk of carrying specific genetic mutations. This allows for informed family planning decisions and, in some cases, the consideration of assisted reproductive technologies.  If carrier screening was not done preconception or if there are specific concerns identified during pregnancy, carrier screening may still be offered during the prenatal period.

Gestational Diabetes: A glucose intolerance test helps identify gestational diabetes, a form of diabetes that can develop during pregnancy and affect both the mother and the baby.

Anemia: Anemia in the mother can be detected through a complete blood count, which measures the levels of red blood cells, hemoglobin, and other components in the blood.

Thyroid function tests: These tests assess the thyroid hormone levels in the mother’s blood. Thyroid disease or dysfunction can impact the health of both the mother and the fetus.

It’s important to note that while these tests can provide valuable information, they are not diagnostic. Further testing, such as diagnostic imaging or invasive procedures like amniocentesis, may be recommended for confirmation of certain conditions. Additionally, the decision to undergo prenatal testing is a personal one, and individuals should discuss their options and concerns with their healthcare providers.

Once a problem is detected are there preventative measures that can be taken during pregnancy?

The preventive measures taken during pregnancy depend on the specific problem detected. Here are some examples:

Chromosomal Abnormalities and Birth Defects:

When a chromosomal abnormality, such as Down syndrome, is identified through prenatal screening tests, it is crucial to recognize that these tests offer a probability of risk rather than a definitive diagnosis. To confirm or rule out such conditions, additional diagnostic procedures like amniocentesis or chorionic villus sampling (CVS) may be advised. Options such as genetic counseling can provide valuable insights, assisting parents in gaining a comprehensive understanding of the potential impact of the condition on their family and facilitating informed choices about the way forward.

Neural Tube Defects:

When a neural tube defect is detected, the healthcare provider may suggest additional diagnostic tests to verify the diagnosis, and in certain instances, surgical intervention might be considered after the baby is born to address the defect. The importance of folic acid supplementation is underscored as a preventive measure against neural tube defects both before and during pregnancy. Women at higher risk may be advised to take a higher dose of folic acid to further mitigate the risk of such developmental abnormalities.

Rh Factor and Blood Type:

The Rh factor is particularly important during pregnancy when the blood of the mother and the fetus may come into contact. If the mother is Rh-negative and the baby is Rh-positive, there is a risk of Rh incompatibility, which can lead to a condition known as Rh isoimmunization or Rh disease.  Rh-negative pregnant women may receive Rh immunoglobulin (RhIg) to prevent Rh incompatibility issues, especially if there is a risk of Rh-positive fetal blood entering the maternal circulation.

Infections:

The approach to managing infections identified during pregnancy screening tests is contingent on the particular nature of the infection in question. Treatable infections may be addressed with medications, whereas others may necessitate vigilant monitoring and comprehensive management strategies. In certain instances, preventive measures, such as vaccination before pregnancy, might be advised to mitigate the risk of specific infections to women and enhance overall maternal and fetal health.

Genetic Disorders:

When carrier screening indicates that both parents carry a genetic condition, seeking genetic counseling becomes pivotal for understanding associated risks and available options. In certain situations, couples may contemplate the use of advanced reproductive technologies, such as pre-implantation genetic diagnosis (PGD). In scenarios where a genetic disorder is conclusively diagnosed, the management plan is contingent upon the specific nature of the condition. Some genetic disorders may offer treatment options or interventions, highlighting the importance of tailored approaches to address each unique circumstance.

Gestational Diabetes:

Gestational diabetes is often managed through lifestyle modifications, including dietary changes and increased physical activity for affected women. In some cases, medication or insulin therapy may be necessary. Regular monitoring and management of blood glucose levels are important to reduce the risk of complications for both the mother and the baby.

Anemia:

Anemia may be treated with iron supplementation and dietary changes to increase iron intake. Regular monitoring of iron levels and other blood parameters is important to ensure that the anemia is adequately managed during pregnancy.

Thyroid Dysfunction:

Thyroid dysfunction may be managed with medication to maintain thyroid hormone levels within the appropriate range. Regular monitoring and adjustments to medication may be necessary throughout the pregnancy.

It’s crucial for individuals to work closely with their healthcare providers to develop a personalized plan based on their specific situation and the nature of the detected issue. In some cases, a multidisciplinary team, including specialists in genetics, maternal-fetal medicine, and other fields, may be involved in the care and management of the pregnancy.

What Benefits Are There to Prenatal Screening Tests for Pregnancy?

Prenatal blood tests provide a range of benefits, offering valuable insights into the health of both the expectant mother and the developing fetus. One significant advantage of screening lies in the early detection of potential issues, particularly in the first and second trimesters of pregnancy. These tests can identify genetic abnormalities and structural defects, enabling timely intervention and management strategies to address any emerging concerns.

Moreover, prenatal blood tests serve as a crucial tool for risk assessment rather than delivering definitive diagnoses. This risk assessment information aids expectant parents and healthcare providers in making informed decisions about the necessity for further diagnostic testing, potential interventions, and preparing for the birth of a child with special needs. Positive results from these tests may prompt recommendations for additional, more invasive diagnostic procedures, such as amniocentesis or chorionic villus sampling (CVS), to either confirm or rule out certain conditions.

Another key benefit is the guidance these tests provide for preventive measures. In cases where known preventive measures exist, such as Rh incompatibility or neural tube defects, prenatal blood tests assist in implementing preventive strategies. This proactive screening approach aims to reduce the risk of complications during pregnancy and childbirth, fostering a healthier outcome for both the mother and the baby through information.

Prenatal blood tests also offer an opportunity for informed decision-making. The early detection of conditions like gestational diabetes or thyroid dysfunction through these tests allows healthcare providers to implement appropriate management strategies, thereby reducing the risk of complications.

Additionally, positive results from carrier screening or genetic screening tests may prompt genetic counseling, providing couples with insights into their risk of passing on certain genetic conditions. This information is pivotal in guiding family planning decisions and, in some cases, influencing the consideration of assisted reproductive technologies.

Emotional preparation is another noteworthy benefit. Early knowledge about potential health concerns allows expectant parents to emotionally prepare for the challenges they may face. It also provides an opportunity to connect with support networks, including medical professionals and support groups, enhancing the overall experience of pregnancy.

Furthermore, prenatal blood tests play a role in monitoring maternal health by routinely assessing factors such as blood type, Rh factor, and overall blood count. This ongoing evaluation is essential for identifying and addressing maternal health issues that may impact the course of the pregnancy.

Other Suggested Second Trimester Screening Tests: PreTRM Test

The PreTRM Test is an innovative blood test that your doctor can order during weeks 18 through 20 of your pregnancy. The test measures proteins in the blood that can indicate if you are at higher risk of delivering early.

One of the many benefits to the PreTRM Test is that parents can prepare for the possibility of a preterm birth.  Because the PreTRM Test is a simple blood draw between 18 and 20 6/7 weeks of gestation (126-146 days).