Frequently Asked Questions

1. What is Maternal-Fetal Medicine Specialist?

An MFM specialist is also known as perinatologist. They are initially trained as an obstetrician-gynecologist (OB/Gyn) and then complete 3 additional years of advanced fellowship training beyond regular OB-GYN residency. The advanced training is focused specifically on the evaluation and management of all complications of pregnancy from the maternal and/or fetal standpoint. Given this additional training, they have specific expertise and additional board certification in handling complex or complicated pregnancies.  This includes significant additional training in diagnostic obstetric ultrasound. In our office, our ultrasound services are also recognized by additional accreditation from the American Institute of Ultrasound Medicine, AIUM.

2. What is the difference between an Ob/Gyn physician and an MFM subspecialist?

Both OB/Gyn (obstetrician-gynecologist) physicians and Maternal-Fetal Medicine (MFM) specialists (also known as a perinatologists) focus on pregnancy care, but they have differences in training and expertise.

Training and background:

  • OB/GYN physician: Completes medical school followed by a 4-year residency in obstetrics and gynecology. This includes broad training in pregnancy care, labor and delivery, postpartum care, gynecologic health, surgeries (e.g., cesarean sections, hysterectomies), and general women’s reproductive health. Following their training, they complete board certification as an Ob/Gyn specialist.
  • MFM subspecialist: Completes medical school followed by the same 4-year Ob/Gyn residency) AND then completes an additional 3 years of fellowship subspecialty training in maternal-fetal medicine. This advanced subspecialty training specifically focuses on managing complex, high-risk pregnancies, fetal conditions, and maternal medical complications. It also includes extensive additional training in obstetrical ultrasound. Following their additional training, they complete double board certification as an On/Gyn specialist AND a Maternal-Fetal Medicine subspecialist.

In short, MFM subspecialists are double board certified high risk pregnancy experts.

3. Can an Ob/Gyn physician manage a high risk pregnancy?

Yes, an Ob/Gyn physician can manage a high risk pregnancy. However, unlike a Maternal-Fetal Medicine specialist, Ob/Gyn physicians do not have specific additional board certification and expertise in the management of high risk pregnancies. For this reason, many Ob/Gyn physicians refer their high risk patients to an MFM specialist for consultation and ongoing follow-up as the pregnancy progresses.

4. When does an Ob/Gyn physician refer to an MFM specialist?

In some cases, based on the patient’s history and high risk factors, the OB/Gyn will refer the patient to an MFM specialist for evaluation early in the pregnancy in order to provide a comprehensive plan to avoid complications. In other cases, the Ob/Gyn will wait until issues arise with the mother or baby and then refer the patient to the MFM later in the pregnancy.

5. Do you have to be referred by an Ob/Gyn to see an MFM specialist?

No, you do not need a referral to see an MFM specialist if you have PPO insurance. However, if you have HMO insurance, you may need to have a referral from your primary Ob/Gyn to see an MFM specialist.

6. What are the conditions that a Maternal-Fetal Medicine subspecialist manages?

  • Multiple gestations (twins, triplets, etc.).
  • Pregnancies complicated by maternal medical conditions (e.g., pre-existing diabetes, chronic hypertension, heart disease, autoimmune disorders, or conditions that develop during pregnancy such as preeclampsia or gestational diabetes).
  • Obstetric complications (e.g., history of preterm birth, prior pregnancy loss/stillbirth, recurrent miscarriage, or issues related to the placenta).
  • Fetal issues (e.g., growth restriction, birth defects/congenital anomalies, genetic conditions, infections, or preterm labor risks).
  • Advanced ultrasound and diagnostic procedures (detailed ultrasounds, genetic testing/counseling, fetal therapy, amniocentesis, etc.).

MFM subspecialists generally work in collaboration with a patient’s primary OB/Gyn, providing consultation and co-management of high risk pregnancies. The goal is to optimize outcomes for both mother and baby through specialized monitoring and surveillance with intervention as needed using evidence-based care.

In short: While most OB/Gyns typically manage uncomplicated/low-risk pregnancies, an MFM specialist steps in when extra expertise is needed to navigate higher risk pregnancies. Therefore, most Ob/Gyns will routinely refer their high risk patients to an MFM specialist for collaborative care.

7. What makes a pregnancy high risk?

A pregnancy is considered high-risk when there is an increased chance of complications for the mother, the fetus, or both, compared to an otherwise uncomplicated “low risk” pregnancy. This means you or your baby may face a higher likelihood of health issues before, during, or after delivery, often requiring closer monitoring and surveillance as well as specific management plans. The closer monitoring and surveillance is typically overseen by a Maternal-Fetal Medicine specialist consultant in collaboration with your primary Ob/Gyn.

The classification “high risk” is determined based on individual factors. Citeria may vary depending on the source cited, but major reputable sources like the ACOG (American College of Obstetricians and Gynecologists), NICHD (National Institute of Child Health and Human Development), Cleveland Clinic, Mayo Clinic, outline common criteria and risk factors as follows:

Key Categories and Factors That Often Lead to a High-Risk Classification (including but not limited to the following)

  1. Advanced Maternal Age
    • As maternal age rises over 35 yo (and particularly over 40 yo), there is a progressive rise in the risk of gestational diabetes, preeclampsia, chromosomal issues, preterm birth, or cesarean delivery. Patients over 40 yo are also at increased risk of stillbirth and require close monitoring, particularly in the latter 3rd trimester
  2. Multiple gestations
    • Twin gestations
    • Triplet gestations
  3. Preexisting (Chronic) Health Conditions (conditions you may have before becoming pregnant):
    • High blood pressure (hypertension)
    • Diabetes (type 1 or type 2)
    • Autoimmune diseases (e.g., lupus, antiphospholipid syndrome)
    • Thyroid disorders (hypothyroidism, hyperthyroidism), asthma, maternal heart disease, kidney disease, seizure disorders, asthma, or blood disorders (e.g. anemia, thalassemia)
    • Obesity (BMI 30 or higher)
    • Mental health conditions (e.g., depression or anxiety requiring medication)
  4. Pregnancy and Obstetric History
    • Prior preterm birth (< 37 weeks’)
    • History of preeclampsia or other complications
    • Prior low birth weight baby in a prior pregnancy
    • Prior cesarean sections (especially multiple) or uterine surgery
    • Previous miscarriages (especially multiple)
    • History of preeclampsia or other complications
    • Prior low birth weight baby in a prior pregnancy
    • Prior cesarean sections (especially multiple) or uterine surgery
  5. Conditions That Develop During Pregnancy
    • Gestational diabetes
    • Preeclampsia or gestational hypertension
    • Severe anemia
    • Placental problems (e.g., placenta previa or accreta)
    • Amniotic fluid abnormalities (such as extra fluid known as polyhydramnios or low fluid known as oligohydramnios)
    • Infections
  6. Fetal or Pregnancy-Specific Factors
    • Suspected fetal abnormalities, genetic conditions, or growth issues (such as fetal growth restriction (FGR) also known as intrauterine growth restriction (IUGR)
    • Rh incompatibility or other blood type issues
  7. Lifestyle and Environmental Factors
    • Exposure to medications which may impact the pregnancy
    • Smoking, alcohol use, or drug use

If any of these apply, your pregnancy may be considered high-risk and may therefore warrant extra precautions, surveillance, and interventions, including low-dose aspirin for preeclampsia prevention (depending on your risk factors), serial ultrasounds to monitor fetal growth and development, fetal monitoring to assess fetal well-being to minimize the risk of stillbirth, and more specific delivery planning.

If you’re concerned or have any of these risk factors which may require additional surveillance, please free to call our MFM office for further guidance and information. We will be happy to coordinate with your Ob/Gyn physician regarding your care. Early MFM evaluation to develop a comprehensive plan of care and close ongoing surveillance are the keys to enabling the best possible outcome for your pregnancy.

8. What is the difference in an ultrasound performed at an OB/gyn office versus an MFM office:

The main differences between an ultrasound performed at a general OB/GYN office versus a Maternal-Fetal Medicine (MFM) office (also called a perinatology or high-risk pregnancy specialist office) are related to the expertise, purpose, level of detail, and equipment.

Key Differences

  • Purpose and Focus
    • OB/GYN office: These are usually routine prenatal ultrasounds for low- to average-risk pregnancies. They check basic things like fetal heartbeat, gestational age (dating), number of babies, Ob/gyn offices sometimes performed the standard midtrimester anatomy scan (which looks at major structures but not always in extreme detail). However, if any questionable findings arise during one of these ultrasounds, the patient is usually referred to an MFM specialist for further evaluation. For this reasone, some Ob/Gyns refer their pstients directly to an MFM specialist for the anatomy scan (whether or not they are considered high risk).
    • MFM office: These focus on high-risk or complicated pregnancies. Ultrasounds are more detailed, targeted, and comprehensive (often called “level II,” “detailed,” or “targeted” ultrasounds). They evaluate fetal anatomy in greater depth, screen for subtle anomalies, assess growth in greater detail, check placental function, use Doppler for blood flow (e.g., in umbilical cord or fetal vessels), and monitor conditions like preterm labor risks, multiples, or maternal issues (e.g., diabetes, hypertension, or prior complications). MFMs often handle specialized scans like fetal echocardiography (detailed fetal heart evaluation) and diagnostic 3D/4D imaging when needed.
  • Expertise and Training
    • OB/GYN: Performed by general obstetricians or their in-office sonographers (ultrasound techs).
    • MFM: Performed by the MFM specialists (perinatologists), who are OB/GYNs with several additional years of fellowship training and additional board certification in high-risk obstetrics and advanced fetal imaging. Sonographers in MFM offices often have specialized certification in obstetric ultrasound and more experience with complex cases. The MFM is trained to provide diagnosis at the time of ultrasound followed by a plan of care recommendation.  Studies show higher detection rates for fetal abnormalities in MFM settings compared to general OB/GYN or radiology offices.
  • Equipment and Image Quality
    • MFM offices typically use state-of-the-art, high-resolution ultrasound machines optimized for fetal detail. Many patients and providers note clearer, more detailed images (e.g., better views of small structures like the fetal brain, heart, kidneys, or spine). General OB/GYN offices may have good equipment for routine needs but not always the latest or most advanced for subtle findings.
  • Other Practical Notes
    • MFM ultrasounds often take longer (30–60+ minutes for detailed scans) and include immediate specialist review/discussion.
    • MFM expertise can lead to earlier/more accurate detection of issues, better monitoring, and improved planning.

9. What are the different type of US performed in an MFM office?

1. Nuchal Translucency (NT) Assessment

This is a first-trimester screening ultrasound (not diagnostic) focused on measuring a small fluid-filled space at the back of the fetus’s neck.

  • Timing: Precisely between 113/7 weeks’ and 13 6/7 weeks’ (when the crown-rump length is 45–84 mm).
  • Purpose: Screens for increased risk of chromosomal conditions (e.g., Down syndrome/trisomy 21, trisomy 18/13) and some structural issues. More fluid often correlates with higher risk. It is usually combined with maternal blood tests (such as cfDNA/NIPT screening). Additional markers like the nasal bone, ductus venosus flow, or tricuspid flow may be assessed.
  • Procedure: Abdominal ultrasound (sometimes transvaginal) is performed to assess the NT measurement. The ultrasound also confirms viability, number of fetuses, and basic early anatomy.
  • Indications: Offered to all pregnant patients as part of first-trimester screening (optional but typically performed in most pregnancies); universally recommended in higher-risk patients
  • Limitations: It is a screening tool only—if abnormal, further testing (e.g., cell-free DNA/NIPT or diagnostic genetic testing such as CVS/amniocentesis) is offered and/or recommended.

2. Targeted Anatomic Survey (also called “Level II” or “Detailed Anatomy Scan”)

This is the comprehensive second-trimester detailed ultrasound that systematically evaluates fetal anatomy.

  • Timing: Typically 18-20 weeks gestation (optimal window for visualization).
  • Purpose: Detects structural congenital anomalies (e.g., heart defects, neural tube defects, kidney issues, limb abnormalities) and assesses overall fetal development. It is more thorough than a standard “Level I” scan.
  • Procedure: Transabdominal ultrasound (with transvaginal assessment of the cervix in most cases); the MFM specialist and/or MFM sonographer images dozens of specific structures in standardized planes (e.g., brain ventricles, four-chamber heart view + outflow tracts, spine, face, abdominal wall, kidneys, bladder, limbs, placenta, and amniotic fluid). Measurements confirm growth and dating.
  • Indications: Routine for many pregnancies, but “targeted”/detailed versions are used for high-risk cases (prior anomaly, abnormal screening, maternal conditions like diabetes). While a basic standard anatomy scan may be sufficient for patients without high risk factors, the targeted anatomic survey provides deeper evaluation for all patients, irrespective of their level of risk

3. Fetal echocardiogram (screening fetal echo)

  • This is a specialized cardiac ultrasound performed by a maternal-fetal medicine specialist or pediatric cardiologist with more specifically detailed views of the heart. The level of detail in this exam is greater than the targeted anatomic survey.
  • Timing: Most commonly 22–23 weeks, but can be done earlier or later if needed.
  • Purpose: Detailed evaluation of the fetal heart’s structure (chambers, valves, great vessels, arches), function (pumping), rhythm, and blood flow. It detects congenital heart defects (CHD), which occur in ~1% of pregnancies and are the most common birth defects.
  • Procedure: Extended transabdominal ultrasound with multiple specialized views (e.g., four-chamber, five-chamber, short-axis, 3 vessel views, ductal and aortic arch views) plus color Doppler and sometimes 3D/4D imaging.
  • Indications: Not routine—triggered by family history of congenital heart defects, suspected abnormality on routine scan, abnormal fetal heart rate/rhythm, maternal conditions (diabetes, lupus, certain medications), IVF pregnancy, or other organ system anomalies.

4. Fetal Growth Assessment (Biometry/Growth Scans)

These are serial late-second and third-trimester ultrasounds that track how the baby is growing.

  • Timing: Usually starts in the late second or third trimester (e.g., 28–32 weeks onward), often every 4 weeks depending on the patient’s risk factors; at least one routine third-trimester scan around 32-36 weeks is increasingly recommended for all pregnancies in some guidelines.
  • Purpose: Monitors fetal size, detects growth restriction (small-for-gestational-age or FGR) or overgrowth (large-for-gestational-age/macrosomia), and evaluates well-being. Late-onset issues are often missed without these scans.
  • Procedure: Measures key biometry (biparietal diameter/BPD, head circumference/HC, abdominal circumference/AC, femur length/FL) to calculate estimated fetal weight (EFW) and plot percentiles. Also checks amniotic fluid volume, placental location/grading, fetal position, and (when needed) Doppler blood flow in the umbilical artery or other vessels.
  • Indications: High-risk pregnancies (hypertension, diabetes, prior FGR, multiples, decreased fetal movement, etc.). Not routine for all low-risk patients, but third-trimester scans improve detection of growth abnormalities compared with fundal height measurement alone.

These scans often overlap or build on each other (e.g., the anatomy scan includes basic heart views that may identify the need for a fetal echo). Results are interpreted in context with your medical history, and follow-up testing or monitoring may be recommended depending on the patient’s history or findings.

10. Is ultrasound safe for the baby?

Obstetric (OB) ultrasounds are safe, non-invasive imaging tests that use high-frequency sound waves to visualize the fetus, placenta, and amniotic fluid during pregnancy. They are performed either transabdominally (most common) or transvaginally and follow guidelines from organizations like the American College of Obstetricians and Gynecologists (ACOG), American Institute of Ultrasound in Medicine (AIUM), and International Society of Ultrasound in Obstetrics and Gynecology (ISUOG).

All of the ultrasounds performed in our MFM office (such as nuchal translucency assessment, targeted anatomic survey, fetal echocardiogram (echo), cervical assessment, and fetal growth assessment—follow the ALARA principle (utilizing energy As Low As Reasonably Achievable) for safety, with no known risks to the fetus when used appropriately.

Additionally, our office is accredited by the American Institute for Ultrasound in Medicine (AIUM). This accreditation includes routine monitoring of the safety of our machines and clinical practices.

Because ultrasound uses high-frequency sound waves (not ionizing radiation like X-rays), it carries no risk of radiation exposure or DNA damage. The primary potential concerns are thermal effects (tissue heating) and non-thermal/mechanical effects (e.g., cavitation, where tiny gas bubbles form and collapse due to pressure changes). These effects are minimal at diagnostic levels.

To minimize any theoretical risks, we emphasize the ALARA principle (“As Low As Reasonably Achievable”):

  • Use the lowest acoustic output/power needed for a clear diagnostic image.
  • Limit scan duration and exposure time.
  • Avoid unnecessary or prolonged scans, especially those without medical benefit
  • Perform scans only when clinically indicated

Routine diagnostic ultrasounds (B-mode for imaging, color Doppler when needed) follow these rules and show no confirmed adverse effects in humans after decades of widespread use.

Thermal Index (TI) and Mechanical Index (MI)

Modern ultrasound machines display two real-time safety indices to help operators stay within safe limits:

  • Thermal Index (TI): Estimates potential temperature rise in tissue (in °C). There are subtypes like TIS (soft tissue), TIB (bone), and TIC (cranial).
    • Safe ranges (per AIUM, ISUOG, and related guidelines):
      • TI ≤ 0.7: No time restrictions for routine obstetric scans (very low risk).
      • TI 0.7–1.0: Commonly used in B-mode/Color Doppler; keep exposure brief if higher.
      • TI >1.0 (especially >2.0–3.0): Limit dwell time significantly (e.g., seconds to minutes depending on value and fetal age); not recommended for prolonged use.
      • In early pregnancy (<10 weeks), monitor TIS; later, TIB for bone heating.
    • Doppler modes (color, pulsed/spectral) generate more heat than standard imaging, so TI is monitored closely, and exposure is kept short (e.g., 5–10 minutes max for first-trimester Doppler in some guidelines).
  • Mechanical Index (MI): Indicates potential for cavitation (mainly a concern with gas bodies, rare in the fetus without contrast agents).
    • FDA limit for obstetric use: MI ≤ 1.9 overall, but often kept ≤1.0 in fetal imaging.
    • MI >0.7: Theoretical cavitation risk increases (though negligible in fetal tissues without lung gas or contrast).
    • Routine B-mode scans typically have MI well below 1.0.

We routinely adjust settings during every exam to keep TI/MI low while obtaining the necessary diagnostic images.

Evidence on Risks and Benefits

  • No confirmed adverse effects: Large reviews, meta-analyses, and long-term follow-up studies (including post-1992 when output limits increased) show no links to birth defects, low birth weight, developmental delays, childhood cancer, hearing issues, or other problems from diagnostic ultrasound.
  • Benefits outweigh risks: Ultrasound improves pregnancy outcomes by confirming viability, dating, detecting anomalies, monitoring growth, and guiding management in high-risk cases. ACOG states ultrasonography is the imaging method of choice in pregnancy due to its safety profile.

In practice, standard obstetric ultrasounds (e.g., nuchal translucency, anatomy survey, growth scans) use low-output modes, and stay well within safe TI/MI ranges. Fetal echoes and detailed Doppler scans requiring more monitoring of but remain safe under guidelines.

If you have concerns about a specific scan or your pregnancy, we are happy to discuss them with you. We use evidence-based standards and can explain the indices displayed during your exam as needed