CT in Pregnancy

Risks and Benefits

Claudia T. Sadro MD, FABR, FRCPC; Theodore J. Dubinsky MD

Appl Radiol. 2013;42(10):6-16.

Abstract and Introduction

Introduction

Pregnant patients may experience nonobstetrical emergencies over the course of their pregnancy, including appendicitis, renal colic, ovarian torsion, hemorrhagic ovarian cysts, trauma, and pulmonary embolism. The utilization of computed tomography (CT) in the diagnosis of diseases such as these has increased in recent years, and the same trend is observed in pregnant women.^[1] Ionizing radiation is a carcinogen and the increased utilization of CT has been cited as a potential cause for an increase in the prevalence of cancer in developed countries.^[2–4] When CT is performed in pregnancy, there is also concern about the teratogenic and carcinogenic effects of ionizing radiation to the developing fetus. In this review article, we will discuss the role of CT in diagnosing nonobstetrical emergency conditions in pregnancy and the risks and benefits to the mother and fetus. For simplicity, we will refer to the conceptus as the fetus. More precisely, the fetus refers to the conceptus after 13 weeks gestational age and the embryo refers to the conceptus before 13 weeks gestational age.

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Table 1. Fetal absorbed doses from selected procedures*
X-Ray Examinations	Fetal Absorbed Dose (mGy)
Cervical spine (AP, lat)	<0.001
Chest X Ray (PA, lat)	0.002
Thoracic Spine X Ray (AP, lat)	0.003
Abdomen X Ray (AP)	1–3
Lumbar Spine X Ray (AP, lat)	1
Limited IVP	6
Barium Enema	7
CT Examinations†	Fetal Absorbed Dose (mGy)
CT Head	0
CT Pulmonary Angiogram	0.2
CT Abdomen	4
CT Abdomen Pelvis	25
CT KUB	10
Background for 9 months of pregnancy†	0.5 - 1

*There are several measurements for radiation dose. The absorbed dose is measured in the rad and the effective dose is measured in the rem. In the international system of units, the rad is measured as the Gray (Gy) and the rem is measured as the Sievert (Sv). 1 rad = 10 mGy and 1 rem = 10 mSV.¹
†CT doses to conceptus and background dose to the conceptus obtained from McCollough CH, Schueler BA, Atwell TD, et al. Radiation exposure and pregnancy: when should we be concerned?
Radiographics. 2007;27:909–917; discussion 917–908 (Reduced dose protocol for CT KUB).

Table 2. In utero effects of diagnostic levels of ionizing radiation (0–250 mGy)*
Gestational age†	Stage of development	Biologic effects to conceptus
0–2 weeks	Pre-implantation	Prenatal death (all or none) Risk at > 50–100 mGy (animal studies)
1–8 weeks	Major organogenesis	Intrauterine growth restriction Risk at > 200 mGy (animal studies)
2–8 weeks	Major organogenesis	Organ malformations > 100 mGy, but not observed in humans at diagnostic levels.
2–15 weeks	Organogenesis and rapid neuronal development and migration	Small head size (SHS) (not necessarily decreased IQ) 100 mGy threshold observed in animals, no threshold observed in Hiroshima survivors
8–15 weeks	Rapid neuronal development and migration	Severe mental retardation (SMR) Not observed < 10 mGy and a threshold of 100 mGy is assumed.
2 weeks to term	Post-implantation	Childhood cancer (< 15 years old) Risk of childhood cancer death 0.06 % per 10 mGy‡ Risk of childhood cancer 0.4 % per 10 mGy§ No threshold.

*Source: Wagner LK, RG Lester and LR Saldana. Exposure of the Pregnant Patient to Diagnostic Radiations. A Guide to Medical Management. Second Edition. Medical Physics Publishing, Madison WI, 1997. Chapter 4: Prenatal risks from ionizing radiations, ultrasound, magnetic fields and radiofrequency waves. pp 77–106.
†The gestational age of the pregnancy is the number of weeks since the mother's last menstrual cycle. It is the number of weeks post conception plus 2 weeks.
‡Background risk of childhood cancer death 0.14%.¹¹
§Absolute lifetime risk of cancer 0.4% per 10 mGy.¹⁵

Table 3. Guidelines for managing pregnant women exposed to diagnostic radiation*
Gestational age	Radiation dose	Adverse biological effects	Recommendation
< 2 weeks post conception†	< 50 mGy	None	None
< 2 weeks post conception†	> 50–100 mGy	Possible spontaneous abortion	None
2–15 weeks post conception†	< 50 mGy	Minimal risk	None
		Childhood cancer (childhood cancer death 0.06% per 10 mGy)
		Absolute cancer risk (0.4 % per 10 mGy)‡
	50–150 mGy	Small head size (0.5–1% per 10 mGy)	Generally, therapeutic abortion is not recommended. However, it may be considered with exposures > 100 mGy in the setting of other risk factors, such as acute viral infection or exposure to teratogenic drugs.
		Mental retardation (0.4% per 10 mGy)
		Childhood cancer (childhood cancer death 0.06% per 10 mGy)
		Absolute cancer risk (0.4 % per 10 mGy)‡
	> 150 mGy	Small head size (15% risk)	Counsel mother about possible therapeutic abortion.
		Mental retardation (6% risk)
		Childhood cancer (childhood cancer death 0.06% per 10 mGy)
		Absolute cancer risk (0.4 % per 10 mGy)‡
> 15 weeks post conception	Any	Childhood cancer (childhood cancer death 0.06% per 10 Gy)	None
> 15 weeks post conception	Any	Absolute cancer risk (0.4 % per 10 mGy)‡	None

*Source: Wagner LK, RG Lester and LR Saldana. Exposure of the Pregnant Patient to Diagnostic Radiations. A Guide to Medical Management. Second Edition. Medical Physics Publishing, Madison WI, 1997. Chapter 10 Stage III The Decision, pp 163–168.
†For 2–8 weeks post conception at > 100 mGy, there is a risk of organ malformations, but organ malformations have never been observed in humans at diagnostic levels.
‡Applegate K and LK Wagner. ACR Practice Guideline for Imaging Pregnant or Potentially Pregnant Adolescents and Women with Ionizing Radiation. In: Resolution 26: American College of Radiology, 2008:1–15

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CT in Pregnancy

Risks and Benefits

Abstract and Introduction

Introduction

Tables

Tables

Tables

References

Authors and Disclosures

Authors and Disclosures

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