Your Pregnancy Matters
4 pregnancy blood tests not all patients need
April 20, 2021
In a previous Your Pregnancy Matters article, we discussed prenatal ultrasound exams that may not be necessary for every patient. This time, we'll focus on prenatal laboratory tests that, though commonly performed, might not benefit all patients, according to Choosing Wisely, a program founded by the American Board of Internal Medicine (ABIM Foundation) and Consumer Reports in 2012.
Certain lab tests during pregnancy can provide invaluable data, but it's important that Ob/Gyns order screenings in the proper context and appropriate combinations. When pregnancy-related lab work provides duplicate or conflicting results, patients and providers may be confused about the proper next steps in a patient's care. Aside from causing undue financial costs, extra appointments, and stress, excess lab tests can lead to unnecessary interventions or treatments.
You have the right to understand what is being recommended and why. Here are four lab tests identified by Choosing Wisely that providers should reconsider recommending for every patient – and that patients should feel empowered to ask about.
1. Inherited thrombophilia evaluation
In patients with past pregnancy complications
About the test: This blood test helps determine whether a patient is at increased risk for inherited thrombophilia – a genetic mutation that increases the risk of developing blood clots during pregnancy.
The test can be useful in assessing recurrence risk and need for preventative treatment in women who have had a prior clot or have a strong family history of clots. However, up to 15 percent of the general population are carriers of Factor V Leiden, the most common inherited thrombophilia mutation.
Being a carrier, especially in the absence of a prior clot history, does not necessarily mean you will have complications, and most patients never develop a clot. When women are tested for unindicated reasons such as prior history of preeclampsia or prior pregnancy loss, positive results can lead to unnecessary stress and possible overtreatment.
When you might not need the test: There is no solid scientific data that inherited thrombophilia causes negative pregnancy outcomes such as preeclampsia, fetal growth restriction, pregnancy loss, or placental abruption. The only treatment for inherited thrombophilia is blood thinners, which are typically not recommended in pregnancy unless the patient has had a previous clot.
Questions to ask your doctor: How will my care change if I test positive? Will those changes increase my chances for a healthy pregnancy?
Potential risks: Taking blood thinners in pregnancy is an ordeal. They must be self-administered with daily shots, which requires additional visits, discomfort, and cost. Taking blood thinners also complicates getting an epidural during labor and increases the risk of bleeding complications during delivery. See the SMFM recommendation.
2. Serum aneuploidy screening after cfDNA aneuploidy screening
About the test: Cell-free DNA (cfDNA) aneuploidy screening is a test that looks for specific fetal abnormalities – missing or extra copies of the chromosomes trisomy 13 (Patau syndrome), 18 (Edwards syndrome), and 21 (Down syndrome).
Serum biochemistry screening looks for these aneuploidies as well but can also be abnormal when other genetic syndromes are present, or may be elevated in women destined to develop pregnancy complications such as preeclampsia or growth restriction . The serum version, however, has a low predictive value for these various abnormal outcomes, particularly when it comes to detecting future pregnancy complications.
When you might not need the test: The general motto is "don't do two screening tests." If cfDNA has already been done, the potential for gathering new, useful information is too low to justify retesting with serum biochemistry screening.
However, your doctor may decide to draw one isolated marker from within the serum biochemistry test known as the alpha-fetoprotein (AFP) as a separate screening test. An elevated AFP can be associated with increased risk of neural tube defects or fetal abdominal wall abnormalities and requires a detailed ultrasound for further evaluation.
Questions to ask your doctor: Which test do you recommend based on the general risk of aneuploidy for my pregnancy? What next steps will you recommend if one or both tests detect aneuploidies?
Potential risks: Patients will have to pay for two tests and may worry about low-risk differences in the results of the two tests. See the SMFM recommendation.
Related reading: How to manage anxiety about pain during common pregnancy tests
3. Routine screenings for cytomegalovirus or toxoplasma antibodies
About the test: Cytomegalovirus (CMV) and toxoplasma are common infections that can becomes serious if they cross the placenta during pregnancy. Risks to the fetus include developmental problems, such as hearing loss.
Patients who have had CMV in the past can get it again. Therefore, even with evidence of CMV-specific antibodies, the baby is still at risk of infection if the mother is reinfected while pregnant.
Current antibody tests for these infections are also not sensitive enough to tell us how long it has been since the patient was infected. So, the screenings are only necessary if there is a clinical indication, such as a history of either virus in pregnancy and/or maternal signs of infection, such as fever.
When you might not need the test: Getting serum screening for CMV or toxoplasma is only appropriate if you have clinical signs of infection or a known exposure. Just knowing that you have the antibodies does not provide substantial information to alter your care.
Questions to ask your doctor: What will be the next steps if I test positive for antibodies? Will you be able to tell whether myself or the baby is infected right now?
Potential risks: Knowing you have the antibodies but that there is no treatment can be stressful. See the SMFM recommendation.
4. Subclinical hypothyroidism screening
In asymptomatic patients
About the test: Hypothyroidism is when the body produces too few thyroid hormones. Subclinical hypothyroidism (SCH) is when total thyroid hormone levels are normal, but serum thyroid-stimulating hormone (TSH) levels are elevated.
A lab test measuring TSH level is often used to screen for possible thyroid dysfunction. However, overt hypothyroidism is only diagnosed if the TSH is elevated and the active thyroid hormone levels are too low.
Approximately 2 to 5 percent of pregnant patients who are otherwise healthy have elevated TSH levels during pregnancy. Some Ob/Gyns and endocrinologists recommend starting SCH treatment during pregnancy, citing concerns about cognitive birth defects, which can be caused by full-blown hypothyroidism.
When you might not need the test: It's rare that SCH would rapidly progress to hypothyroidism during pregnancy. Large clinical studies have shown there is no cognitive benefit to children born in women who were treated for SCH in pregnancy.
Questions to ask your doctor: What treatment will you recommend if I have SCH? What are the chances I will develop hypothyroidism during pregnancy?
Potential risks: SCH treatment requires paying for medication and follow-up visits with an endocrinologist, with no recognized benefit to the patient or baby. See the SMFM recommendation.
A few closing thoughts
Ob/Gyn laboratory tests, when thoughtfully ordered, can provide valuable insights and help guide your care toward the best possible outcomes. But not every test is appropriate for every patient.
Talk with your doctor about any lab tests you have questions about. We're here to give you the answers and information you need to have a happy, healthy pregnancy.