Imaging During Pregnancy | WellAlly

Quick Answer: Ultrasound is completely safe during pregnancy and is the preferred imaging modality for prenatal evaluation. MRI is also safe, especially after the first trimester, because it uses no radiation. X-rays and CT scans expose the fetus to radiation and should be avoided unless medically necessary—but when needed for serious or life-threatening conditions, the risk is very small with appropriate shielding and dose reduction. The key principle is that imaging during pregnancy should only be performed when the benefit to the mother outweighs the potential risk to the fetus, and the safest modality that answers the clinical question should be chosen.

For expecting mothers, understanding imaging safety helps reduce anxiety while ensuring you receive necessary medical care. This guide explains what every pregnant woman should know about medical imaging safety.

How Radiation Affects the Fetus

Radiation exposure during pregnancy carries potential risks that depend on:

Gestational age: The fetus is most vulnerable to radiation during the first trimester (weeks 1-12), when organs are forming. Later in pregnancy, the fetus is more resistant to radiation effects.

Radiation dose: Higher radiation doses carry greater risk. Medical imaging typically uses doses far below the threshold for harmful effects.

Type of effect: Radiation can cause:

• Deterministic effects: Dose-dependent effects like fetal growth restriction or microcephaly that only occur above a threshold dose (typically 50-100 mGy)
• Stochastic effects: Random effects like childhood cancer that can theoretically occur at any dose, though the risk is very small at low doses

Radiation dose thresholds for fetal harm:

• Less than 50 mGy: No proven harmful effects
• 50-100 mGy: Possible effects, but risk is very low
• Greater than 100 mGy: Increased risk of fetal harm, including congenital abnormalities and intellectual disability

Actual Radiation Doses from Medical Imaging

Typical fetal radiation exposure:

• Chest X-ray: 0.0005-0.01 mGy (negligible risk)
• Pelvic X-ray: 1-4 mGy (very low risk)
• CT head: 0 mGy to fetus (outside the scan range)
• CT chest: 0.01-0.1 mGy (negligible risk)
• CT abdomen/pelvis: 8-50 mGy (depends on trimester and shielding)
• Nuclear medicine: Variable depending on the radiopharmaceutical

Context: Natural background radiation exposes us all to approximately 3 mGy per year. A single pelvic X-ray exposes the fetus to about the same radiation as a few months of natural background exposure.

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Key Finding: No diagnostic imaging study exposes the fetus to more than 50 mGy when appropriate techniques and shielding are used—well below the threshold for proven harmful effects. Even CT scans of the abdomen and pelvis typically deliver less than 25-30 mGy to the fetus.

Source: American College of Radiology, 2024 Reference: ACR Practice Parameter: Imaging Pregnant or Potentially Pregnatic Patients

Ultrasound: Completely Safe

Ultrasound uses sound waves (not radiation) to create images and is the preferred imaging modality during pregnancy.

Safety advantages:

• No ionizing radiation: Completely safe for the fetus at any gestational age
• Real-time imaging: Allows visualization of fetal movement and blood flow
• Widely available: Most facilities have ultrasound equipment
• No known risks: Over 50 years of use have shown no harmful effects

Common uses during pregnancy:

• Dating and viability: Confirming pregnancy, determining due date, checking for fetal heartbeat
• Anatomy scan: Detailed evaluation of fetal anatomy at 18-22 weeks
• Growth monitoring: Tracking fetal growth throughout pregnancy
• Amniotic fluid assessment: Measuring amniotic fluid volume
• Placenta location: Identifying placenta previa or other placental problems
• Doppler studies: Evaluating blood flow in the umbilical cord and fetal vessels

3D/4D ultrasound: Uses the same sound waves as standard ultrasound, arranging them into three-dimensional images. No additional safety concerns beyond standard 2D ultrasound.

Safety note: While ultrasound is very safe, it should only be performed for medical reasons, not for purely entertainment purposes ("keepsake" ultrasound). The FDA discourages non-medical fetal ultrasound.

MRI: Safe After First Trimester

MRI uses magnetic fields and radio waves (not radiation) to create detailed images. MRI is considered safe during pregnancy, especially after the first trimester.

Safety profile:

• No ionizing radiation: Like ultrasound, MRI uses no radiation
• Gadolinium concern: MRI contrast (gadolinium) crosses the placenta and should be avoided during pregnancy unless absolutely essential
• First trimester caution: Many facilities avoid MRI during the first trimester (weeks 1-12) out of an abundance of caution, though no harm has been proven
• Second and third trimester: MRI without contrast is considered safe

Common uses during pregnancy:

• Fetal brain evaluation: When ultrasound findings are abnormal or inadequate
• Placental abnormalities: Evaluating placenta accreta, invasive placentation
• Maternal abdomen/pelvis: Appendicitis, ovarian masses, other maternal conditions
• Fetal MRI: Detailed evaluation of fetal organs, especially brain, lungs, and abdomen

MRI during pregnancy considerations:

• No sedation: Pregnant patients should not be sedated for MRI
• Comfort: The MRI table may be uncomfortable late in pregnancy
• Noise: MRI is loud, but ear protection is provided
• Length: MRI scans take 30-60 minutes; you'll lie on your back which may be uncomfortable

Gadolinium contrast during pregnancy: Generally avoided because:

• Crosses the placenta and enters the fetus
• Animal studies show potential harm to developing fetuses
• Human safety data are limited

Use gadolinium during pregnancy only when:

• No alternative test provides necessary information
• The information is essential for the health of the mother or fetus
• The benefit clearly outweighs potential risk

X-Ray Safety Principles

General X-ray safety during pregnancy:

• Inform technologist of pregnancy: Always tell the technologist if you're pregnant or possibly pregnant
• Abdominal shielding: A lead apron over your abdomen shields the fetus from scatter radiation
• Lowest dose possible: Technologists use the lowest radiation dose that provides diagnostic images
• Targeted imaging: Only the necessary body area is imaged
• Justification: X-rays should only be performed when medically necessary

Common X-Ray Scenarios

Chest X-ray:

• Fetal dose: 0.0005-0.01 mGy (negligible)
• Safety: Very safe during pregnancy when needed
• Shielding: Abdominal shielding further reduces fetal exposure
• Common uses: Pneumonia, chest trauma, heart failure, line placement verification

Extremity X-rays (arms, legs, hands, feet):

• Fetal dose: Essentially zero (outside the imaging area)
• Safety: Completely safe during pregnancy
• Shielding: Usually not necessary (no scatter to abdomen)
• Common uses: Fractures, arthritis, foreign body detection

Dental X-rays:

• Fetal dose: Negligible (very focused beam, lead apron used)
• Safety: Safe during pregnancy when needed
• Shielding: Lead apron and thyroid collar are standard
• Timing: Elective dental X-rays can often be postponed until after pregnancy, but urgent dental care shouldn't be delayed

Abdominal/pelvic X-rays:

• Fetal dose: 1-4 mGy depending on the study
• Safety: Low but non-zero risk; only used when medically necessary
• Justification: Usually avoided if alternatives exist
• Common uses: Kidney stones, intestinal obstruction, trauma

CT Radiation Exposure

CT scans use higher radiation doses than standard X-rays, requiring careful consideration during pregnancy.

Fetal radiation doses:

• CT head: 0 mGy (fetus outside scan range)
• CT chest: 0.01-0.1 mGy (very low risk)
• CT abdomen/pelvis: 8-50 mGy depending on gestational age and shielding

CT risk assessment:

• CT head: No fetal risk (scan doesn't include fetus)
• CT chest: Minimal fetal risk (far from fetus, low scatter)
• CT abdomen/pelvis: Low but measurable risk; justify necessity and consider alternatives

When CT During Pregnancy Is Appropriate

CT head during pregnancy:

• Indications: Head trauma, severe headache, neurological symptoms, suspected stroke
• Safety: No radiation to fetus (outside scan area)
• Alternatives: MRI is often preferred when available and appropriate

CT chest during pregnancy:

• Indications: Pulmonary embolism, pneumonia, chest trauma
• Safety: Very low fetal radiation dose
• Alternatives: Ventilation-perfusion (V/Q) nuclear scan for pulmonary embolism (also delivers some radiation), chest X-ray for pneumonia

CT abdomen/pelvis during pregnancy:

• Indications: Appendicitis, kidney stones, trauma, bowel obstruction
• Safety: Higher fetal radiation dose; use only when:
  • Condition is serious or life-threatening
  • Alternative imaging (ultrasound, MRI) is inadequate or unavailable
  • Delayed diagnosis could be more harmful than the radiation risk
• Alternatives: Ultrasound (first-line for many conditions), MRI (especially for appendicitis)

Risk-benefit example: For suspected appendicitis in a pregnant woman:

• Delaying diagnosis: Risk of ruptured appendix, which can cause serious infection, preterm labor, or fetal loss
• CT radiation: Approximately 20-30 mGy to fetus—well below the 50-100 mGy threshold for harmful effects
• Decision: CT is often appropriate when ultrasound is inconclusive and appendicitis is suspected, because the risk of a ruptured appendix outweighs the very low radiation risk

CT Techniques to Reduce Fetal Exposure

When CT during pregnancy is necessary, radiologists use special techniques to minimize fetal radiation exposure:

Reduced tube current: Lower radiation settings

• Reduced kVp: Lower energy X-rays (when diagnostically acceptable)
• Limited scan range: Scanning only the essential area
• Automatic exposure control: Technology that adjusts radiation based on body thickness
• Shielding: Lead shielding over the abdomen (when not in the direct scan field)
• Single-phase imaging: Scanning once instead of multiple phases with and without contrast
• MRI first: Using MRI when possible to avoid CT entirely

Nuclear medicine involves injecting, swallowing, or inhaling small amounts of radioactive material. The radiation risks to the fetus vary depending on the specific radiopharmaceutical.

Common Nuclear Medicine Studies

Ventilation-Perfusion (V/Q) Scan:

• Indications: Evaluating for pulmonary embolism
• Fetal dose: 0.1-0.5 mGy (low risk)
• Safety: Safer than CT pulmonary angiogram for fetus during pregnancy
• Considerations: Preferred over CT for pulmonary embolism in pregnancy

Technetium Bone Scan:

• Indications: Evaluating bone metastases, infection, fractures
• Fetal dose: 4-5 mGy (low risk)
• Safety: Avoid if alternatives exist; use if medically necessary

Thyroid Scan:

• Indications: Evaluating thyroid nodules, hyperthyroidism
• Fetal dose: 4-20 mGy depending on the isotope used
• Safety: Generally avoided during pregnancy; ultrasound is preferred

PET Scan:

• Indications: Cancer staging, evaluating tumors
• Fetal dose: Approximately 10-25 mGy from FDG radiotracer
• Safety: Avoided during pregnancy when possible; use only if essential

Nuclear medicine breastfeeding considerations: Some radiopharmaceuticals appear in breast milk. Mothers may need to:

• "Pump and dump" breast milk for a specified time (usually 12-48 hours depending on the agent)
• Temporarily formula feed while the radiopharmaceutical clears

Abdominal Pain During Pregnancy

Evaluation approach:

1. Ultrasound first: No radiation, excellent for most obstetric and many abdominal causes
2. MRI second: No radiation, excellent for appendicitis and other abdominal conditions
3. CT only if needed: When ultrasound and MRI are inconclusive or unavailable

Common causes:

• Appendicitis: Ultrasound or MRI (CT if these are inadequate)
• Gallbladder disease: Ultrasound (first choice)
• Kidney stones: Ultrasound (may miss small stones; CT if diagnosis uncertain)
• Ovarian pathology: Ultrasound (first choice)
• Uterine rupture/abruption: Ultrasound (first choice)

Shortness of Breath During Pregnancy

Evaluation approach:

1. Chest X-ray: Very low fetal dose, appropriate for pneumonia, heart failure
2. V/Q scan: Preferred over CT for pulmonary embolism evaluation
3. CT chest: Higher radiation; use if V/Q unavailable or inconclusive

Common causes:

• Pulmonary embolism: V/Q scan preferred over CT pulmonary angiogram
• Pneumonia: Chest X-ray (very low fetal dose)
• Asthma exacerbation: Chest X-ray if needed
• Peripartum cardiomyopathy: Chest X-ray (very low fetal dose)

Trauma During Pregnancy

Evaluation approach:

• Minor trauma: Usually no imaging needed; fetal monitoring may be sufficient
• Moderate to severe trauma: Imaging as needed to evaluate the mother
  • CT head: No fetal risk (outside scan area)
  • CT cervical spine: Minimal fetal risk
  • CT chest/abdomen/pelvis: Use if traumatic injury suspected; fetal risk is usually outweighed by maternal benefit

Accidental Pregnancy During Imaging

If you discover you're pregnant after having imaging:

• Don't panic: Most imaging studies carry very low fetal risk
• Calculate gestational age: Risk is highest during first trimester
• Estimate fetal dose: Your radiologist can estimate the fetal radiation dose
• Discuss with your obstetrician: They can help put the risk in perspective
• Consider specialized counseling: For high-dose exposures, genetic counseling may be helpful

Reassurance: Most accidental fetal exposures from diagnostic imaging are far below the 50-100 mGy threshold for harmful effects. Even at doses of 5-50 mGy, the absolute risk of harmful effects is very small.

Radiation Workers and Pregnancy

Women who work with radiation (radiologic technologists, interventional cardiologists, etc.) can continue working during pregnancy with appropriate precautions:

• Wear fetal dosimeters: To monitor radiation exposure
• Double lead shielding: Wear two lead aprons for additional protection
• Limit fluoroscopy time: Reduce involvement in procedures requiring fluoroscopy
• Increase distance: Step back from the radiation source when possible
• Modify duties: Some facilities offer modified duties during pregnancy

IVF and Early Pregnancy Imaging

Women undergoing fertility treatment often have early pregnancy ultrasounds before they know they're pregnant. Early ultrasound is safe and standard practice. If other imaging (X-ray, CT) was performed before pregnancy was recognized:

• Don't panic—most accidental exposures happen at very low doses
• Calculate the gestational age at exposure
• Discuss with your fertility specialist or obstetrician

Questions to Ask

When your doctor recommends imaging during pregnancy, ask:

1. What specific diagnosis are we looking for? Understanding the clinical question helps assess urgency and necessity.

2. Is this imaging essential for my health or my baby's health? Some imaging can be delayed until after pregnancy; other imaging is urgently needed.

3. What are the risks of NOT doing this imaging? Sometimes the risk of missing a serious condition outweighs the imaging risk.

4. Is there a safer alternative that provides the same information? Ultrasound and MRI are safer than X-ray/CT when they can answer the clinical question.

5. What are the radiation risks to my baby? For X-ray and CT, your doctor or radiologist can explain the specific risks.

6. Will my abdomen be shielded? For most X-rays, abdominal shielding further reduces fetal exposure.

7. Is the contrast safe during pregnancy? IV contrast (iodinated or gadolinium) crosses the placenta and requires special consideration.

Shared Decision-Making

Imaging decisions during pregnancy should involve:

• Your obstetrician: Coordinating your overall prenatal care
• The radiologist: Determining the safest imaging approach
• You: Understanding risks and benefits to make an informed decision

Sometimes imaging is clearly necessary (serious illness, trauma). Other times, there's more flexibility to delay imaging or use alternatives. Discussing your specific situation with your doctors ensures the best outcome for both you and your baby.

1. Ultrasound is completely safe during pregnancy and is the preferred imaging modality for prenatal evaluation.

2. MRI without contrast is safe during pregnancy, especially after the first trimester, because it uses no radiation.

3. X-rays carry very low risk when medically necessary, especially with abdominal shielding and appropriate technique.

4. CT scans should be avoided when safer alternatives (ultrasound, MRI) are available, but may be appropriate for serious conditions when benefits outweigh risks.

5. Radiation risks are dose-dependent: Most diagnostic imaging delivers fetal doses well below the 50-100 mGy threshold for harmful effects.

6. First trimester is most sensitive: The fetus is most vulnerable during weeks 1-12 when organs are forming.

7. Gadolinium contrast should be avoided during pregnancy when possible; MRI without contrast is preferred.

8. Nuclear medicine risks vary: Some studies (like V/Q scan for PE) are relatively safe, while others are avoided during pregnancy.

9. Always inform your healthcare providers if you're pregnant or possibly pregnant before any imaging procedure.

10. Imaging during pregnancy is a risk-benefit decision: When serious or life-threatening conditions need evaluation, the benefit to the mother nearly always outweighs the very small fetal risk from appropriately performed imaging.

Disclaimer: This guide provides general information about imaging during pregnancy. Always consult your obstetrician and radiologist about the specific risks and benefits of any imaging test during your pregnancy. Individual circumstances vary, and your healthcare team can provide personalized guidance.

Last Updated: March 2026 Next Review: September 2026