13.2: Prenatal Testing during the First Trimester
By the end of this section, you will be able to:
- Explain the purpose and results of ultrasound examinations performed in the first trimester of pregnancy
- Explain the purpose and results of maternal assays and multiple marker screenings performed in the first trimester of pregnancy
- Explain the purpose and results of cell-free DNA
- Explain the purpose and results of carrier screening
- Explain the purpose and results of chorionic villus sampling
- List the routine lab tests performed in the first trimester of pregnancy
- Discuss the patient education and nursing actions required when assisting with prenatal testing in the first trimester
The American College of Obstetricians and Gynecologists ( ACOG ) recommends that all pregnant persons be offered prenatal genetic assessment through screening and diagnostic tests regardless of risk factors (American College of Obstetricians and Gynecologists [ACOG], 2020c). A screening is a test used during pregnancy to identify whether a fetus is more or less likely to have certain birth defects, many of which are genetic disorders. Genetic testing allows patients the opportunity to seek counseling for obstetric management and recommendations, early referral to pediatric subspecialists, or earlier and safer pregnancy termination if the results are abnormal. Common reasons for prenatal testing are listed in Table 13.1. Unfortunately, some pregnant persons cannot afford expensive screening.
| Factor | Indications |
|---|---|
| Maternal |
|
| Fetal |
|
| Obstetric |
|
The decision to have prenatal screening is up to each pregnant person. A positive screening indicates a higher risk of the fetus having a genetic, chromosomal, or structural abnormality. Further diagnostic testing is needed to confirm a diagnosis. Some couples choose to have prenatal testing to plan for medical care their child may need. Other couples choose to terminate the pregnancy if the results are abnormal.
Ultrasound
An ultrasound is a safe and painless diagnostic procedure that allows health-care providers to see inside the uterus and examine the developing fetus without invasive measures (ACOG, 2017a). Ultrasounds use high-frequency sound waves to detect objects in their path and return the waves as echoes. The returning sound waves return as two or three-dimensional images that show the structure of the densities detected. Some expectant persons may undergo ultrasound in their first trimester to confirm the pregnancy.
During pregnancy, health-care providers use two main types of ultrasound: transvaginal and abdominal. Transvaginal ultrasound scans are usually performed in the first trimester and require the bladder to be empty. The indications for a first trimester ultrasound are as follows:
- Estimate gestational age.
- Help screen for certain genetic disorders.
- Count the number of fetuses.
- Check the fetus’s heart rate.
- Check for suspected ectopic pregnancy .
- Evaluate pelvic pain.
- Evaluate vaginal bleeding.
- Evaluate suspected trophoblastic disease.
- Measure nuchal translucency.
- Evaluate pelvic mass.
- Provide information as an adjunct to chorionic villus sampling (William et al., 2023).
Ultrasound for Confirmation of Pregnancy
In early pregnancy, a transvaginal ultrasound scan may be recommended to identify the presence or absence of an intrauterine gestational sac and evaluate if the pregnancy is viable. It will also look at the ovaries and fallopian tubes of the patient to check for any abnormalities. Ultrasound can also assist in assessing suspected ectopic pregnancies, multiple gestation, or any other pregnancy-related complications (ACOG, 2017a). During the first trimester, a transvaginal ultrasound scan may be recommended following a positive human chorionic gonadotropin ( hCG ) level to establish the gestational age of the pregnancy. The gestational sac can be detected at 5 to 6 weeks. The fetal pole and cardiac activity are detectable by ultrasound at 6 weeks (Murugan et al., 2020).
For a transvaginal ultrasound, educate the patient that a transvaginal probe encased in a disposable cover and coated with gel will be inserted into the vagina. The patient may be asked to insert this probe themselves. The patient will be instructed to lie on their back with their knees bent, and the ultrasound technician will assist with positioning. The transvaginal ultrasound is performed with the bladder empty.
Patient-Centered Care
The nurse will focus on the patient’s understanding and ensure privacy and comfort during the transvaginal ultrasound.
- During a transvaginal ultrasound, the nurse educates the patient on the procedure.
- The nurse must ensure the patient is draped and feels comfortable.
- The nurse will assess for pain or discomfort during the procedure.
- If the patient is in pain during the procedure, the nurse will advocate for the patient’s comfort.
- The nurse will assess for pain or stress after the procedure.
- If the patient continues to have pain after the procedure, the nurse will report symptoms to the health-care provider.
During an abdominal ultrasound exam, the gel is spread over the abdomen, and the ultrasound technician moves the transducer over the abdomen to produce the picture (Figure 13.2). The patient can be positioned to see the images if desired. The patient may be asked to come to the ultrasound exam with a full bladder to help displace the intestines and evaluate the uterus with better visibility.
Nuchal Translucency
The nuchal translucency screening is an ultrasound scan that measures the thickness of space at the back of the fetus’s neck, known as the nuchal fold thickness. This screening assesses the risk of trisomy 21 (Down syndrome) and heart, abdominal wall, and skeleton defects. Nuchal translucency screening is usually done between 11 and 14 weeks of gestation (Mount Sinai Health System, 2022).
Abdominal ultrasound will be used to perform this test to measure the nuchal fold. During pregnancy, it is common for fetuses to have some fluid at the back of their neck. However, if the fetus has Down syndrome or another genetic disorder , there may be an increase in the amount of fluid present, causing the space to appear thicker on an ultrasound. (Mount Sinai Health System, 2022) (Figure 13.3).
A nuchal translucency measurement is taken to determine the risk of the fetus having trisomy 21, or Down syndrome. When the results of the nuchal translucency test are normal, it is unlikely that the fetus has Down syndrome or any other genetic disorder (Mount Sinai Health System, 2022). However, if an excess amount of fluid (greater than or equal to 3 mL) is at the back of the neck, the test result is positive. This indicates that the fetus is at a higher risk of having trisomy 21 ( Down syndrome ), trisomy 18 , trisomy 13 , Turner syndrome , or congenital heart disease . The health-care provider may recommend an amniocentesis if the nuchal translucency screening returns an abnormal result (Mount Sinai Health System, 2022).
In addition to the ultrasound, a multiple marker blood test will also be performed. The ultrasound and blood test results are analyzed to determine the risk of the fetus having Down syndrome or another genetic disorder (Mount Sinai Health System, 2022).
Effect of Age on Antepartum Testing
The risk of fetal genetic disorders in pregnancy increases with advanced maternal age of 35 or greater. With each year over 35, the risk of genetic disorders and pregnancy complications increases. Prenatal screening recommendations for advanced maternal age include:
- first trimester ultrasound
- detailed fetal anatomic ultrasound
- ultrasonogram for growth assessment in the third trimester
- prenatal genetic screening (serum screening with or without nuchal translucency ultrasound or cell-free DNA screening)
- diagnostic testing (chorionic villus sampling or amniocentesis)
(ACOG, 2022b)
Maternal Assays
Prenatal genetic screening and diagnostic testing should be offered to all pregnant persons regardless of their age and risk of chromosomal abnormalities. Early and regular prenatal care helps to establish the accurate dating of the pregnancy due to the gestation-specific timing of maternal assay testing. The nurse has an important role in educating pregnant persons about the different prenatal screenings. Every pregnant person should have the opportunity to accept or refuse the recommended screenings.
Multiple Marker Screen
A multiple marker screen is a blood test for pregnant persons that screen for chromosomal disorders and neural tube defect s. Between 10 and 14 weeks of pregnancy, a screening (also known as integrated screen part 1 ) can be performed using PAPP-A and free B-hCG markers. If PAPP-A levels are low before the 14th week, there may be an increased risk of Down syndrome and trisomy 18. Conversely, high levels of hCG may indicate an increased risk of Down syndrome. An ultrasound scan is also used to measure fetal nuchal translucency, indicating an increased risk for Down syndrome if the measurement is higher than normal for fetuses of the same age (Shiefa et al., 2013). The ultrasound and blood work results are combined with the pregnant person’s age to calculate the risk of the fetus having Down syndrome, trisomy 18, or other defects (Palka et al., 2019).
Alpha-Fetoprotein
The alpha-fetoprotein ( AFP ) test is a blood test that measures the level of alpha-fetoprotein in the pregnant person’s blood. AFP is dispersed from fetal plasma into fetal urine and excreted into the amniotic sac. This screening can be measured from maternal serum or from amniotic fluid . The AFP test is considered a screening, not a diagnostic test. An abnormal result does not mean the developing fetus has an abnormality but suggests a potential increase in risk (Chen et al., 2022). Measurement of the alpha-fetoprotein L2 variant in the first trimester combined with the PAPP-A markers, free B-hCG, and nuchal translucency can also demonstrate an increase in fetal risk of trisomy 21 (Chen et al., 2022).
Cell Free DNA (cfDNA)
A cell-free DNA (cfDNA) screening is a blood test that can be done as early as 10 weeks’ gestation and up until delivery that screens for certain conditions caused by an abnormal number of chromosomes. This test does not screen for all types of chromosomal disorders and is not diagnostic. Should the results come back abnormal, additional testing, like an amniocentesis or chorionic villus sampling (CVS), would be needed to confirm a diagnosis (U.S. National Library of Medicine, 2021b).
The maternal blood sample obtained is analyzed for an abnormal amount of DNA from chromosomes 21, 18, and 13. This test screens for trisomy 21 (Down syndrome), trisomy 18 ( Edwards syndrome ), and trisomy 13 ( Patau syndrome ) (U.S. National Library of Medicine, 2021b). Cell-free DNA results are most accurate in screening for trisomy 21, 18, and 13 and for pregnant persons at higher risk for genetic disorders (Raymond et al., 2022).
Cell-free DNA screening may be recommended for patients at high risk of having a fetus with a chromosome disorder. This population includes:
- persons who are 35 or older
- persons with a history of having a previous baby with a chromosome disorder
- persons with abnormal ultrasound results
- persons with other abnormal prenatal tests
Some health-care providers offer this screening to all pregnant persons, regardless of their risk factors. This screening is low risk for complications because it involves just a blood draw, and it has a high accuracy rate compared to other prenatal screenings. It generally takes around a week to receive the results. If the results come back negative, it is unlikely the fetus has a chromosomal disorder. However, if the results are positive, the fetus is at risk for having a chromosomal disorder, and further testing is needed to confirm a diagnosis. (U.S. National Library of Medicine, 2021b).
Carrier Screening
A carrier screening can determine if a pregnant person or their partner carries a gene for specific genetic disorders. This screening can be done either before or during pregnancy and offers valuable insights into the probability of having a child with a genetic disorder. To determine if one partner is a carrier, a sample of blood, saliva, or cheek tissue is collected and tested. The partner with the higher likelihood of being a carrier is typically tested first. If the initial test comes back negative, no further testing is required. However, if the results indicate that the first partner is a carrier, the other partner will also undergo testing (ACOG, 2020a).
Carrier screening is usually looking for recessive disorders. If a person has the gene for a disorder but does not manifest symptoms of the disorder, they are a carrier. Because a carrier does not have the disorder, they often do not know that they are a carrier. When both parents carry the gene for a disorder, their child has a 25 percent chance of inheriting the gene from each of them and developing the disorder. Additionally, the child has a 50 percent chance of being a carrier of the disorder. However, if only one parent is a carrier, the child has a 50 percent chance of also being a carrier of the disorder but will not develop the disorder (ACOG, 2020a). For a more detailed explanation, see 4.2 Genetics.
Persons considering pregnancy or currently pregnant should be offered carrier screening for cystic fibrosis , hemoglobinopathies , and spinal muscular atrophy. Patients also have the option to undergo targeted or expanded carrier screening for other disorders. Targeted carrier screening tests for disorders based on ethnicity or family history. Expanded carrier screening is done without regard to race or ethnicity (ACOG, 2022a).
If the pregnant person and partner are both carriers of a genetic disorder, diagnostic testing can be done on the fetus with each pregnancy to determine if the fetus has the disorder. Some couples who are both carriers choose to use in vitro fertilization (IVF) with donor eggs or sperm to get pregnant. This option allows the embryo to be tested for the disorder before it is transferred to the uterus. Other couples who are both carriers may choose not to have children or to adopt a child (ACOG, 2020a).
Carrier screening results are private health information. It is against the law for health insurers to request genetic testing results or use them to determine coverage, rates, or preexisting conditions, according to the Genetic Information Nondiscrimination Act of 2008 ( GINA ). GINA also prohibits employers from discriminating against employees or job seekers based on genetic information, but this law does not apply to life insurance, long-term care insurance, or disability insurance (ACOG, 2020a).
Prenatal genetic testing is performed to both confirm normality of the fetus and screen for or diagnose abnormalities. Take this quiz on prenatal genetic testing to test your knowledge.
Chorionic Villus Sampling (CVS)
A chorionic villus sampling (CVS) is a prenatal diagnostic test conducted between the 10th and 13th week of pregnancy to diagnose fetal chromosomal, metabolic, or DNA abnormalities. This test involves taking a biopsy of the placental tissue (chorionic villi) (Jones & Montero, 2022). CVS cannot diagnose neural tube or body wall defects, as those require measuring alpha-fetoprotein (AFP) levels. CVS is generally recommended for persons with the following risk factors:
- abnormal cell-free DNA test
- first trimester abnormal ultrasound
- history of having a child with a structural birth defect, genetic disease, chromosomal abnormality, or metabolic disorder
- advanced maternal age (35 or older) or paternal age (50 or older) by pregnancy due date
- parental carrier of a chromosomal rearrangement
- parental carrier of autosomal recessive disease
- parental carrier of a genetic disorder such as Tay-Sachs disease , sickle cell disease , or neurofibromatosis
There are contraindications to having CVS. Extra care is required with patients who are taking anticoagulant medication. In addition, patients with a bloodborne infectious disease, like human immunodeficiency virus (HIV) infection or hepatitis, should be informed that there is a potential risk of transmitting the disease vertically during CVS testing (Jones & Montero, 2022).
Before the procedure, a maternal-fetal specialist must obtain informed consent from the pregnant person. The pregnant person may also receive genetic counseling and counseling about the procedure before having it performed. A blood type and screen will be performed to determine if the patient requires Rho(D) immune globulin ( RhoGAM ) if they are Rh negative. Before the CVS, an ultrasound exam will be conducted to verify the gestational age of the fetus by measuring the crown-rump length, checking fetal heart activity, and determining the location of the placenta and cord insertion site (Jones & Montero, 2022).
A skilled provider and an ultrasonographer will perform the CVS. The CVS procedure can be done transcervically, where a catheter is inserted through the cervix and then into the placenta to obtain the tissue sample (Jones & Montero, 2022). Alternatively, it can be performed transabdominally, where a needle is inserted through the abdomen and uterus and then into the placenta to obtain the tissue sample (Jones & Montero, 2022). The nurse can assist with making sure that the pregnant person is as comfortable as possible, preventing patient movement, and explaining what to expect during the procedure to help decrease anxiety. Postprocedure patient education should include no intercourse or tub baths for 2 weeks or as directed by the provider; immediately notify the health-care provider of any fever or vaginal bleeding, leaking of fluid, or discharge; and go to the follow-up appointment.
According to Jones and Montero (2022), chorionic villus sampling carries risks similar to those of amniocentesis. These risks include the potential for pregnancy loss, bleeding, infection, ruptured membranes, limb defects, and uncertain test results (Jones & Montero, 2022).
Routine Prenatal Lab Tests
In addition to blood tests done for genetic screening, other blood tests are performed during pregnancy. These tests are described in more detail in Chapter 11 Prenatal Care and include (but are not limited to):
- complete blood count (CBC)
- blood type and Rh factor
- rubella
- hepatitis B and hepatitis C
- sexually transmitted infections
- human immunodeficiency virus (HIV)
A CBC is recommended to assess for anemia, which is common in pregnancy. Typing the patient’s blood and determining their Rh factor are recommended. An antibody screen is also recommended to determine the presence of an antibody that could affect the fetus. A urinalysis is performed to check for possible signs of urinary tract disease or infection. If a urinary tract infection (UTI) is suspected, a urine culture will be done to test for bacteria, and antibiotics will be needed to treat the UTI.
Testing for rubella is recommended in all pregnant persons because this disease can cause birth defects if the patient is infected during pregnancy. Hepatitis, a virus that infects the liver, can be passed to the fetus during pregnancy. Routine screening for hepatitis B and C is recommended for all pregnant persons (ACOG, 2021e). All pregnant persons should be tested for sexually transmitted infections (STIs) during pregnancy. Syphilis, chlamydia, HIV, and gonorrhea testing is performed at the first prenatal visit. STI testing is recommended in early pregnancy but may also be repeated in later pregnancy based on the age and risk factors of the patient and facility policy, as STIs can cause complications to both the fetus and patient. HIV can be transmitted to the fetus; however, the rate of transmission is significantly decreased when antiretrovirals are taken during pregnancy.
Nurse’s Role
Nurses may be involved in planning, implementing, and administering or evaluating first trimester screenings and tests. While nurses can be trained to collect blood samples or other lab specimens, many facilities may use lab technicians.
Nurses should be aware of recommended screenings to better educate pregnant persons who may need to undergo prenatal testing and lab tests. It is important for nurses to understand why a test is recommended or ordered so that they can provide appropriate information and support to the pregnant person and their partner or family. Information about recommended screening is summarized in (Table 13.2). Nurses who work in a perinatal care practice setting will need to have more in-depth knowledge of pregnancy screenings and tests.
| Testing | Criteria |
|---|---|
| Screening | |
| Carrier testing |
|
| First trimester marker screening |
|
| Cell-free DNA screening |
|
| Diagnostic Tests | |
| Chorionic villus sampling (CVS) |
|
Because pregnancy screening is voluntary, patients may refuse it. With any screening process, the first step is for the health-care provider to obtain informed consent. Nurses will need to educate their patients on what each screening or test is recommended for, what it can detect, what a positive screening suggests, and that the pregnant person may accept or reject a screening. After the pregnant person has been educated on the recommended screening or test, the health-care provider will obtain informed consent to signify that the pregnant person was given appropriate information on the screening and understands the risks and benefits of it (Gordon et al., 2023).
The health-care team will need to notify the pregnant person of the results, explain what the results mean, and talk to the pregnant person about any additional testing or referrals that the provider recommends. The team member should allow time for the pregnant person to ask questions. It may be appropriate for the pregnant person to discuss the options with their provider in person, and the pregnant person should be given a contact number to call if they have any additional questions (Gordon et al., 2023).