What does 10 CFR 35.3047 require?

It requires a licensee to report a dose to an embryo/fetus that exceeds 50 mSv (5 rem) dose equivalent resulting from a radiopharmaceutical administration to a pregnant individual, unless that dose was specifically approved in advance by the authorized user. It also requires reporting a dose to a nursing child greater than 50 mSv (5 rem) total effective dose equivalent, or a dose that results in unintended permanent functional damage to an organ or physiological system, from an administration to a breast-feeding individual.

How is a 35.3047 report different from a medical event under 35.3045?

A medical event under 35.3045 is defined by the dose differing from what was prescribed by set thresholds and percentages. A 35.3047 report is specifically about an embryo/fetus or a nursing child receiving a dose above its own absolute thresholds from an administration. The same incident can sometimes meet both rules, but they are separate reporting obligations with separate criteria.

Is 35.3047 the same as the occupational fetal dose limit?

No. The occupational limit in 10 CFR 20.1208 — 0.5 rem (5 mSv) to the embryo/fetus of a declared pregnant worker over the entire pregnancy — applies to staff exposure. 10 CFR 35.3047 applies to a patient's embryo/fetus or a nursing child exposed because of a radiopharmaceutical administered to the pregnant or breast-feeding patient. They are different populations, different thresholds, and different rules.

Who is responsible for preventing and reporting these events?

The Radiation Safety Officer, the authorized user, and the licensee share responsibility. The RSO ensures pregnancy screening, breastfeeding instructions, and reporting procedures are in place; the authorized user controls the clinical decision and any pre-approval of fetal dose; and the licensee owns the notification and corrective-action obligations under the license and NRC rules.

Reporting Fetal and Nursing-Child Dose: 35.3047

Q: What are the notification timelines for a 35.3047 event?

The licensee must notify the NRC Operations Center by telephone no later than the next calendar day after discovery, and submit a written report to the appropriate NRC Regional Office within 15 days after discovery. The written report must include certification that the pregnant individual or mother (or responsible relative or guardian) was notified, or an explanation of why not.

Q: How do these events usually happen?

The most common root causes are an unrecognized pregnancy at the time of administration, a missed or incorrect pregnancy screen, and a failure to instruct a breast-feeding patient to interrupt nursing after certain radiopharmaceuticals. Therapeutic radioiodine given to an unrecognized pregnancy is the classic high-dose scenario.

A dose to an embryo/fetus or a nursing child from a radiopharmaceutical administration is a specific reportable event under 10 CFR 35.3047 — not the same thing as a medical event under 35.3045, and not the same thing as the occupational fetal-dose limit under 20.1208. Mixing up these three is one of the more common conceptual errors in a nuclear medicine radiation-safety program, and it leads to both missed reports and misdirected worry.¹²³

10 CFR 35.3047 sets absolute dose thresholds for the patient's embryo/fetus or nursing child, specific notification timelines, and a requirement to notify the affected individual. Understanding it — and the screening practices that prevent these events — is core Radiation Safety Officer (RSO) knowledge.¹

Introduction

Most radiopharmaceutical administrations to a pregnant or breast-feeding patient never approach the 35.3047 thresholds, which is exactly why a rare one can slip through. A diagnostic study carries a comparatively small fetal dose; the events that trigger 35.3047 are usually either an unrecognized pregnancy at the time of a higher-dose administration — therapeutic radioiodine is the classic example — or a failure to instruct a breast-feeding patient to interrupt nursing after an administration that concentrates in breast milk.¹⁶

For an RSO, 35.3047 is less about memorizing a number and more about building a program that keeps the number from ever being reached: a reliable pregnancy screen, a documented breastfeeding-instruction step at release, authorized-user involvement in any borderline decision, and a reporting workflow that works on the one day you need it. This article lays out the exact regulatory requirements, distinguishes the three fetal/child dose rules that are easy to confuse, and describes the preventive and reporting practices that make a defensible program.

Topic Explanation

What 10 CFR 35.3047 actually says

10 CFR 35.3047 addresses two distinct populations exposed because of an administration to a patient:¹

Embryo/fetus. The licensee must report a dose to an embryo/fetus greater than 50 mSv (5 rem) dose equivalent that results from an administration of byproduct material (or radiation from byproduct material) to a pregnant individual — unless the dose to the embryo/fetus was specifically approved, in advance, by the authorized user.
Nursing child. The licensee must report a dose to a nursing child, from an administration to a breast-feeding individual, that is greater than 50 mSv (5 rem) total effective dose equivalent, or that has resulted in unintended permanent functional damage to an organ or a physiological system of the child, as determined by a physician.

The "specifically approved in advance" clause for the embryo/fetus matters: if an authorized user knowingly and deliberately accepts a fetal dose as part of a clinical decision (for example, a necessary therapy in a known pregnancy where the benefit is judged to outweigh the risk and this is documented in advance), that planned dose is not the unexpected event the rule is designed to capture. The rule targets unintended or unapproved exposures.¹

The three rules people confuse

Rule	Who is exposed	Threshold	Context
10 CFR 35.3047	Patient's embryo/fetus	more than 50 mSv (5 rem) dose equivalent	Administration to a pregnant patient, not pre-approved
10 CFR 35.3047	Patient's nursing child	more than 50 mSv (5 rem) TEDE, or unintended permanent functional damage	Administration to a breast-feeding patient
10 CFR 20.1208	Declared pregnant worker's embryo/fetus	5 mSv (0.5 rem) over the entire pregnancy	Occupational exposure of staff

The occupational rule, 20.1208, is a dose limit for staff and is an order of magnitude lower (5 mSv) because it governs routine, controllable occupational exposure; it is supported by NRC Regulatory Guide 8.13 and the declared-pregnancy process.³⁶ The 35.3047 thresholds (50 mSv) are reporting triggers for a patient's embryo/fetus or nursing child. Same anatomy, entirely different regulatory logic and numbers.

How 35.3047 differs from a medical event (35.3045)

A medical event under 10 CFR 35.3045 is defined by how much the delivered dose or dosage differs from what was prescribed: broadly, a dose that differs from the prescribed dose by more than 0.05 Sv (5 rem) effective dose equivalent, 0.5 Sv (50 rem) to an organ or tissue, or 0.5 Sv (50 rem) shallow-dose equivalent to the skin, together with a total dose or dosage differing by 20% or more (or falling outside the prescribed range), as well as wrong-radiopharmaceutical, wrong-route, or wrong-individual administrations.² 35.3047 is not about deviation from a prescription; it is about an embryo/fetus or nursing child receiving a dose above its own absolute threshold. One incident can meet both rules, but they are evaluated independently.¹²

Key Technical Principles

The reporting thresholds in both unit systems

NRC rules state limits in SI with the traditional unit in parentheses. The embryo/fetus and nursing-child thresholds are both 50 mSv = 5 rem. The conversion is definitional:

1 rem = 10 mSv

Worked example. Suppose an inadvertent administration to an unrecognized pregnancy is later estimated to have delivered a fetal dose equivalent of 65 mSv. Converting and comparing to the threshold:

H_{E / F} = 65 mSv \times \frac{1 rem}{10 mSv} = 6.5 rem > 5 rem

Because 6.5 rem exceeds the 5 rem (50 mSv) threshold and the dose was not approved in advance by the authorized user, the event is reportable under 35.3047(a). A planned, pre-approved therapeutic fetal dose of the same magnitude would not be, because the "specifically approved in advance" exception applies.¹

The occupational fetal-dose summation (a related but separate calculation)

For context, the occupational embryo/fetus dose under 20.1208 — which applies to staff, not patients — is assessed as the sum of external and internal contributions to the declared pregnant worker:

H_{E / F} = H_{deep} (mother) + H_{internal}

where $H_{deep}$ is the deep-dose equivalent to the declared pregnant worker and $H_{internal}$ is the dose from radionuclides in the embryo/fetus and in the worker. This is capped at 5 mSv over the pregnancy, with a provision deeming compliance when the pregnancy is declared late.³ It is shown here only to make the contrast with 35.3047 explicit: do not apply the occupational 5 mSv figure to a patient's fetus, and do not apply the 50 mSv reporting threshold to staff.

Why radioiodine and breast-milk tracers dominate the risk

Fetal dose from most diagnostic nuclear medicine is well below 50 mSv, so the embryo/fetus reporting threshold is typically reached only with therapeutic administrations — most importantly I-131 for thyroid conditions, which crosses the placenta and, after the first trimester, concentrates in the fetal thyroid. An unrecognized pregnancy at the time of radioiodine therapy is the scenario that most often produces a reportable fetal dose.¹⁶

For the nursing child, the concern is radiopharmaceuticals that are excreted in breast milk. Some agents require interruption of breastfeeding for a defined period, and a few effectively require cessation; failure to give that instruction at release can lead to a reportable nursing-child dose or unintended harm.¹⁵ For the clinical details, see our guide to breastfeeding interruption after radiopharmaceuticals.

Clinical Impact

These are low-frequency, high-consequence events, which is the hardest category for any safety program. Because they almost never happen, the screening and instruction steps that prevent them can quietly erode — a pregnancy question that becomes a checkbox nobody reads, a breastfeeding instruction that is verbal and undocumented. The impact of getting it wrong is severe: potential harm to a fetus or infant, a reportable regulatory event, mandatory individual notification, and the reputational and enforcement consequences that follow.¹

Getting it right is mostly preventive. A reliable pregnancy screen before any administration with meaningful fetal-dose potential, a documented breastfeeding status and instruction at release, and authorized-user engagement in any borderline case prevent nearly all 35.3047 events. When one does occur, a program that already knows the thresholds, the one-calendar-day notification, the 15-day written report, and the individual-notification requirement can respond correctly under pressure instead of improvising.¹²

Practical Optimization Tips

Prevent the event

Require and document a pregnancy screen appropriate to the administration. For therapeutic radioiodine and other higher-dose administrations, treat pregnancy exclusion as a hard stop, not a formality.¹⁶
Capture breastfeeding status at the same point and attach the correct interruption or cessation instruction to the release documentation for agents excreted in milk.¹⁵ See patient release after radiopharmaceutical therapy.
Involve the authorized user in any case where a pregnant or possibly pregnant patient may need an administration, and document any deliberate, pre-approved fetal dose in advance — the exception in 35.3047(a) only protects a dose that was actually approved beforehand.¹

Be ready to report

Keep the thresholds and timelines where the on-call team can find them: NRC Operations Center by telephone no later than the next calendar day after discovery; written report to the appropriate NRC Regional Office within 15 days.¹
Build the individual-notification step into the workflow. The written report must certify that the pregnant individual or mother (or responsible relative or guardian) was notified, or explain why not.¹
Preserve the dosimetry basis. A defensible fetal- or nursing-child-dose estimate — administered activity, timing, and the dose model used — is what supports both the report and the clinical follow-up.

Keep the three rules straight

Train staff that 20.1208 (5 mSv, occupational, declared pregnant worker) and 35.3047 (50 mSv, patient's embryo/fetus or nursing child) are different rules for different people.¹³
Evaluate a possible 35.3047 event and a possible 35.3045 medical event independently; one incident can be both.¹² See medical event reporting under 35.3045.

Regulatory Considerations

10 CFR 35.3047 is an NRC medical-use reporting rule, administered by the NRC or by an Agreement State under an equivalent regulation. Across DRPS service areas, Florida, Maryland, Virginia, California, Nevada, Pennsylvania, New York, and New Jersey are NRC Agreement States that enforce their own compatible version of Part 35, while Washington DC and Delaware are direct-NRC jurisdictions for byproduct material. In every case the substance of the rule is the same: the 50 mSv thresholds, the next-calendar-day telephone notification, the 15-day written report, and the individual-notification requirement.¹

The rule sits inside a web of related requirements an RSO should cross-reference:

10 CFR 35.3045 defines the medical event and its own notification timeline; evaluate both rules for any administration gone wrong.²
10 CFR 20.1208 and Regulatory Guide 8.13 govern the separate, lower occupational embryo/fetus limit for declared pregnant workers.³⁶
10 CFR 35.75 governs release of patients containing byproduct material and is where breastfeeding-interruption instructions are anchored.⁵
10 CFR 20.1003 provides the governing definitions, including "embryo/fetus" and "declared pregnant woman."⁴

Programs should maintain written procedures that reference these rules together, so that the person evaluating a possible event is not deciding in the moment which rule applies. Always confirm the exact wording and any Agreement State variations with the authority having jurisdiction.

Frequently Asked Questions (FAQs)

What dose to an embryo/fetus must be reported under 35.3047?

A dose greater than 50 mSv (5 rem) dose equivalent resulting from a radiopharmaceutical administration to a pregnant individual, unless the authorized user specifically approved that dose in advance.¹

What dose to a nursing child must be reported?

A dose greater than 50 mSv (5 rem) total effective dose equivalent from an administration to a breast-feeding individual, or a dose that results in unintended permanent functional damage to an organ or physiological system of the child as determined by a physician.¹

How quickly must we report?

Notify the NRC Operations Center by telephone no later than the next calendar day after discovery, and submit a written report to the appropriate NRC Regional Office within 15 days after discovery. The written report must certify that the affected individual (or responsible relative or guardian) was notified, or explain why not.¹

Is this the same as the medical-event rule?

No. 35.3045 is about the delivered dose differing from what was prescribed by defined thresholds and percentages; 35.3047 is about a patient's embryo/fetus or nursing child exceeding its own absolute dose threshold. The two are evaluated separately, and one event can trigger both.¹²

Does the occupational 5 mSv fetal limit apply to patients?

No. The 5 mSv (0.5 rem) limit in 20.1208 applies to the embryo/fetus of a declared pregnant worker — a staff-exposure limit. It does not apply to a patient's embryo/fetus, which is governed by the 50 mSv reporting threshold of 35.3047.¹³

Key Takeaways

10 CFR 35.3047 requires reporting a dose over 50 mSv (5 rem) to a patient's embryo/fetus (unless pre-approved by the authorized user) or over 50 mSv TEDE to a nursing child, plus any unintended permanent functional damage to the child.¹
It is distinct from a medical event (35.3045), which is defined by deviation from the prescribed dose, and from the occupational fetal limit (20.1208, 5 mSv for declared pregnant workers).²³
Notification is next-calendar-day by telephone to the NRC Operations Center and a 15-day written report, with certified individual notification.¹
The high-risk scenarios are therapeutic radioiodine in an unrecognized pregnancy and missed breastfeeding-interruption instructions.¹⁵⁶
Prevention — reliable pregnancy screening, documented breastfeeding instructions, and authorized-user engagement — is where an RSO adds the most value.¹⁶

Conclusion

10 CFR 35.3047 is short, but it governs two of the most consequential exposures a nuclear medicine program can cause: a dose to a patient's embryo/fetus or to a nursing child. The regulation's power comes from clarity — absolute 50 mSv thresholds, a next-calendar-day call, a 15-day written report, and a duty to tell the affected individual — and from keeping it distinct from the medical-event rule and the occupational fetal-dose limit it is so often confused with. A program that screens reliably for pregnancy, documents breastfeeding instructions, engages the authorized user in borderline decisions, and keeps the reporting steps at hand will almost never have a 35.3047 event, and will handle the rare one correctly.¹²³

How DRPS Can Help

Diagnostic Radiation Physics Services (DRPS) supports nuclear medicine and radioactive-material programs across Florida, Maryland, Virginia, Washington DC, California, Nevada, Pennsylvania, New York, New Jersey, and Delaware with Radiation Safety Officer support and radioactive material license support: pregnancy-screening and patient-release procedures, breastfeeding-interruption guidance, event-reporting workflows, dosimetry support for fetal and nursing-child dose estimates, and radiation-safety-program audits. Our board-certified medical physicists help you build procedures that prevent these events and respond correctly when one occurs.

Whether you need to strengthen pregnancy and breastfeeding screening or prepare your reporting workflow, we can help. Learn more about medical physicist consulting or contact DRPS.

Related Resources

References

U.S. Nuclear Regulatory Commission. 10 CFR 35.3047, Report and notification of a dose to an embryo/fetus or a nursing child. nrc.gov
U.S. Nuclear Regulatory Commission. 10 CFR 35.3045, Report and notification of a medical event. nrc.gov
U.S. Nuclear Regulatory Commission. 10 CFR 20.1208, Dose equivalent to an embryo/fetus. nrc.gov
U.S. Nuclear Regulatory Commission. 10 CFR 20.1003, Definitions (Standards for Protection Against Radiation). nrc.gov
U.S. Nuclear Regulatory Commission. 10 CFR 35.75, Release of individuals containing unsealed byproduct material or implants containing byproduct material. nrc.gov
U.S. Nuclear Regulatory Commission. Instruction Concerning Prenatal Radiation Exposure. Regulatory Guide 8.13, Revision 3. Washington, DC: NRC; 1999. nrc.gov
U.S. Nuclear Regulatory Commission. Release of Patients Administered Radioactive Material. Regulatory Guide 8.39. Washington, DC: NRC; 1997. nrc.gov
U.S. Nuclear Regulatory Commission. Consolidated Guidance About Materials Licenses: Program-Specific Guidance About Medical Use Licenses. NUREG-1556, Volume 9, Revision 3. nrc.gov
International Commission on Radiological Protection. Pregnancy and Medical Radiation. ICRP Publication 84. Ann ICRP. 2000;30(1). icrp.org
International Commission on Radiological Protection. Radiological Protection in Medicine. ICRP Publication 105. Ann ICRP. 2007;37(6). icrp.org