6 pregnancy ultrasound exams you might not need
April 13, 2021
Choosing Wisely was founded by the American Board of Internal Medicine (ABIM Foundation) and Consumer Reports in 2012 to identify medical tests and treatments that were overused and potentially not helpful for patients.
The initiative encourages patient-provider discussions about exams that are focused on whether the recommended test is:
- Free from harm
- Financially worthwhile for the patient
- Not duplicative of other tests or exams
- Potentially going to lead to adverse implications
The Society for Maternal-Fetal Medicine (SMFM) created Choosing Wisely’s recommendations related to obstetric care. In a 2021 publication, Choosing Wisely identifies 20 commonly recommended actions that may not necessarily benefit all pregnant patients, six of which involve ultrasound testing. We've put together talking points for you to use with your provider about what the tests entail, when the exam might not be necessary, and questions to ask your doctor.
You have the right to understand what is being recommended and why. Ultrasound is a valuable tool that is used throughout pregnancy to assess risk and diagnose potential complications. It is safe and can help determine whether your baby is growing as expected, or whether something might not be developing properly.
But more isn't always better when it comes to ultrasound.
As useful as it can be, non-indicated use of ultrasound technology can lead patients and providers down rabbit holes that may cause more harm than good. Providers may recommend a range of tests that their practice views as routine, but that may not be necessary, resulting in extra visits and extra costs for the patient.
1. Doppler blood flow study to measure fetal growth restriction
About the exam: Placental changes can restrict blood flow to and from the baby and may lead to a small baby – one whose weight is below the tenth percentile for its age. Doppler blood flow studies in the umbilical cord show how well blood is flowing from the fetus to the placenta.
When you might not need the exam: If the baby is average size and growing as expected, the Doppler study likely won't provide any useful information. In fact, it could potentially falsely flag a placental issue.
Questions to ask your doctor: Is my fetus small enough to worry about blood flow in the umbilical cord? What is the next step if the result is abnormal?
Potential risks: Concerns about the placenta can lead to additional exams and testing, which may result in unnecessary interventions such as induction of labor. The longer the fetus can stay inside, the more it can develop. See the SMFM recommendation.
2. Routine cervical length screening
Outside 16-24 weeks with no preterm birth symptoms
About the exam: Cervical length measurement may help identify patients whose babies are at risk for preterm birth. However, the screening is most beneficial for patients with a history of preterm birth or cervical incompetency.
When you might not need the exam: This study is only reliable in low-risk, asymptomatic women when cervical length is measured between 16 and 24 weeks of pregnancy. Done earlier or later, it doesn't provide useful information.
Getting a baseline cervical length at the 20-week anatomy ultrasound is reasonable. But knowing the cervical length alone can't reliably predict outcomes for patients with no other health risks.
Questions to ask your doctor: Do I have other risk factors for premature birth? If my cervix measures short, how will my prenatal care change?
Potential risks: It's possible that what we consider a short cervix is perfectly safe and healthy for your anatomy. Labeling you as having a "short cervix" without other risk factors can lead to undue stress, bed rest recommendations, or cerclage placement, which carries a risk of infection and disturbance of the cervical tissue. See the SMFM recommendation.
3. Cervical length measurement after cerclage placement
About the exam: Cerclage is a suture that can be placed in the cervix if a patient has cervical incompetency, in which the cervix starts to dilate without contractions.
The goal of the suture is to keep the cervix closed in an attempt to prevent pregnancy loss. By measuring cervical length via ultrasound after cerclage placement, some providers feel they can see whether the cerclage is helping.
When you might not need the exam: Research shows that measurement of the full cervical length or the area below the cerclage does not correlate to specific trends in outcomes. Unfortunately, there is no further treatment beyond cerclage for a short cervix, and bed rest is not shown to provide benefit.
Questions to ask your doctor: What will you recommend if my cervix is shortening?
Potential risks: Continuing to measure can be reassuring for some patients – if their measurement doesn't change. But if the cervix shortens, measuring can cause unnecessary anxiety, and the patient may inappropriately be encouraged to go on bed rest. Repeated measurements can be costly and time consuming for the patient. See the SMFM recommendation.
4. Extra testing when gestational diabetes is controlled with diet, exercise
About the exam: Nonstress tests (NSTs) monitor the fetal heart rate. Biophysical profiles (BPPs) – NST plus fetal monitoring through an ultrasound–evaluate breathing, muscle tone, and overall fetal well-being.
Patients who need medication to control gestational diabetes are at increased risk of adverse outcomes, such as stillbirth. However, patients whose gestational diabetes is well-controlled with diet and exercise are not at increased risk for stillbirth.
When you might not need the exam: If your gestational diabetes is under control without medication, NST and BPP are probably unnecessary.
Questions to ask your doctor: Will this test tell us anything new related to the gestational diabetes? What happens if you find something else that is concerning?
Potential risks: Additional imaging and fetal monitoring can lead to false positive results. Investigating those new concerns may result in more appointments, charges, or unnecessary interventions such as induction of labor. See the SMFM recommendation.
5. Diagnostic testing when a sonogram shows just one aneuploidy soft marker
If the pregnancy is at low risk for genetic conditions
About the exam: Certain sonogram findings, especially when found together, can be a sign of aneuploidy – genetic conditions such as Down syndrome. Two of these "soft markers" include:
- Echogenic intracardiac focus (EIF): A microcalcification on the heart muscle that occurs in approximately 5 percent of pregnancies.
- Choroid plexus cyst (CPC): Pools of fluid in a part of the brain that makes spinal fluid. CPC occurs in approximately 2 percent of pregnancies.
When you might not need the exam: When found alone, each is considered to be normal sonogram findings if the fetus has no other risk factors for Down syndrome or the patient has no other factors putting her at increased risk for having a baby with a chromosome abnormality. Also, the cell free DNA screening for Down syndrome – taken from a maternal blood sample – is nearly 99 percent accurate. If yours was negative, more tests likely will not provide new information.
Questions to ask your doctor: What additional testing are you recommending? How will further testing compare to my cfDNA results?
Potential risks: Invasive testing that disturbs the fetus, such as amniocentesis, carries a risk of pregnancy loss. In patients with low risk for aneuploidy in pregnancy, additional testing will add cost and stress with no real benefit. See the SMFM recommendation.
6. Amniotic fluid index to diagnose oligohydramnios
About the exam: Measuring the level of amniotic fluid – the liquid that surrounds a fetus in the womb – can indicate how well the placenta is functioning.
If the level is normal, we can assume placental function and blood flow to the baby's kidneys is normal. Amniotic fluid pockets lower than 2cm – oligohydramnios – can lead to pregnancy loss.
When you might not need the exam: Checking the amniotic fluid level is important. However, it's important to get this information in the most appropriate way. There are two ways to measure:
- Examining the pockets of fluid in all four quadrants of the uterus
- Checking a single pocket of fluid in one quadrant
One pocket's measurement should be sufficient. If we check all the pockets, there's a chance we'll get a mixed bag of results – inconclusive, and probably nothing to worry about, but still potentially unnerving for the patient.
Questions to ask your doctor: How was the amniotic fluid measured? If the fluid is low, what are my options?
Potential risks: If the fluid level is low, your provider might recommend induction of labor. However, delivery before 39 weeks of gestation increases the risk of health complications for the newborn. See the SMFM recommendation.
A few closing thoughts
Your Ob/Gyn relies on you to provide insights into your needs, beliefs, and preferences about prenatal care. Ask questions if you don't understand a specific recommendation, and focus on the benefits, risks, and how test results might change your plan of care.
These conversations are not meant to challenge your doctor – they're meant to open a dialogue. At the end of the day, talking with your doctor about ultrasound exams will support a healthy, happy pregnancy – and avoid unnecessary, potentially costly medical tests and exams.