Pregnancy Imaging Guide

CT/MRI

RCR/RCOG2021IR(ME)R 2017SI 2017/1322RCR iRefer2017, continuously updatedNICE NG1582020v2.0 · March 2026

Routine

EDInpatientOutpatient

General Principles

— ALL of the following must be met

Benefit to the mother must outweigh the potential risk to the fetus — untreated maternal pathology (e.g., PE, appendicitis) carries greater risk than diagnostic imagingRCR/RCOG
Avoid elective CT in the first trimester where possible — defer non-urgent ionising radiation investigations until after delivery or use non-ionising alternativesRCR/RCOG
Never withhold a clinically indicated CT in pregnancy — delay in diagnosis of serious maternal pathology poses greater risk than the radiation dose
Informed consent must be obtained and documented, including discussion of fetal radiation dose and risk in lay termsIR(ME)R 2017
Pregnancy status must be established before any ionising radiation exposure in women of childbearing age — local '28-day rule' or pregnancy testing policy appliesIR(ME)R 2017

— ALL of the following must be met

Fetal dose <50 mGy is considered safe with no measurable increase in fetal anomaly, intellectual disability, or childhood cancer risk — most diagnostic CT examinations deliver well below this thresholdRCR/RCOG
CT head (~0 mGy fetal dose) and CT chest (~0.1 mGy fetal dose) deliver negligible fetal radiation and should not be withheld in pregnancyRCR/RCOG
CT abdomen/pelvis delivers the highest fetal dose (~10–25 mGy depending on gestation and technique) but remains well below the 50 mGy thresholdRCR/RCOG
Abdominal lead shielding is no longer routinely recommended for CT (limited efficacy, may impair image quality with ATCM) — discuss with medical physics if concerned
Iodinated IV contrast may be used when clinically necessary — no proven teratogenic effect; neonatal thyroid function should be checked within the first week of life if contrast given in 3rd trimesterRCR/RCOG

— ALL of the following must be met

V/Q SPECT preferred over CTPA in pregnancy due to significantly lower maternal breast dose (V/Q ~0.3 mGy vs CTPA ~3–10 mGy)RCR/RCOG
Fetal dose from both CTPA (~0.1 mGy) and V/Q scanning is very low and clinically negligibleRCR/RCOG
CTPA may be used when V/Q is unavailable, when CXR is abnormal (V/Q less interpretable), or when alternative diagnosis is suspected (e.g. aortic dissection, pneumonia)NICE NG158
Chest X-ray should be performed first — if normal, V/Q preferred; if abnormal, CTPA is preferredRCR/RCOG
Compression leg ultrasound should be considered if clinical suspicion of DVT — a positive result may obviate the need for chest imaging

— ALL of the following must be met

MRI is considered safe at any gestation — no ionising radiation; no proven harmful effects on the fetus from magnetic fields or radiofrequency energy at clinical field strengthsMHRA MRI Safety
1.5T is preferred over 3T in pregnancy as a precautionary measure — 3T may be used if 1.5T is unavailable and the clinical need is pressing
MRI may be performed in the first trimester when clinically indicated — there is no evidence of harm, though some centres prefer to defer elective MRI until after the first trimester
MRI is the preferred second-line investigation (after ultrasound) for suspected appendicitis in pregnancy — avoids ionising radiationRCR iRefer

— ALL of the following must be met

Gadolinium-based contrast agents should be avoided in pregnancy unless the information is essential and cannot be obtained by other meansRCR BFCR(19)4
If gadolinium is deemed essential, use macrocyclic agents only (gadobutrol, gadoteridol, gadoteric acid) at the lowest effective doseRCR BFCR(19)4
Administration requires senior radiology approval (consultant radiologist) with documented justification
Animal studies suggest possible teratogenic effects at high doses; human data are limited but large cohort studies have shown possible association with rheumatological/inflammatory conditions in exposed offspring

— ALL of the following must be met

Ultrasound is the first-line imaging modality in pregnancy for abdominal, pelvic, and obstetric indications — no ionising radiation, no known harmful effects, widely available
Graded-compression ultrasound for suspected appendicitis — sensitivity reduced in later pregnancy but remains appropriate first-line investigation
Ultrasound for renal colic assessment — physiological hydronephrosis of pregnancy may mimic obstruction; correlation with clinical features essential

— ALL of the following must be met

Iodinated contrast: safe to continue breastfeeding — less than 1% of maternal dose is excreted in breast milk, and less than 1% of that is absorbed by the infant's GI tract
Gadolinium contrast: safe to continue breastfeeding — less than 0.04% of maternal dose is excreted in breast milk; no interruption recommended
Mothers may be reassured that breastfeeding can continue without interruption after either iodinated or gadolinium contrast — no evidence of harm to the infant

— ALL of the following must be met

Written informed consent is recommended for CT in pregnancy — document that risks and benefits have been discussed, including estimated fetal doseIR(ME)R 2017
Record the estimated fetal dose in the radiology report or supplementary dose record — liaise with medical physics for formal dose estimation if fetal dose may approach 50 mGy
Document gestational age at time of exposure — this affects estimated fetal dose and the organs at risk
Document the clinical justification and the name of the authorising IR(ME)R practitionerIR(ME)R 2017

Warning

Never withhold a clinically indicated CT in pregnancy — maternal risk from undiagnosed pathology outweighs fetal radiation risk

Information

Fetal dose from most diagnostic CT examinations is well below 50 mGy and is not associated with measurable harm

Warning

Gadolinium should be avoided in pregnancy unless essential — macrocyclic agents only, with consultant radiologist approval

Information

Breastfeeding may continue without interruption after iodinated or gadolinium contrast

Information

V/Q SPECT preferred over CTPA in pregnancy due to lower breast dose; CTPA when V/Q unavailable or CXR abnormal

RCR/RCOG

v2.02026-03-08New cross-cutting pregnancy imaging guidance