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Bởi vì hydronephrosis là một phát hiện bình thường trong đa số trường hợp có thai, sự hiện diện của nó không thể được thực hiện như là một dấu hiệu của một hòn đá ureteric có thể. Siêu âm là một cách không đáng tin cậy của chẩn đoán sự hiện diện của sỏi trong thai | 152 J. REYNARD obstruction. Because hydronephrosis is a normal finding in the majority of pregancies its presence cannot be taken as a sign of a possible ureteric stone. Ultrasound is an unreliable way of diagnosing the presence of stones in pregnant and in nonpregnant women. In a series of pregnant women ultrasound had a sensitivity of 34 i.e. it misses 66 of stones and a specificity of 86 for detecting an abnormality in the presence of a stone i.e. false-positive rate of 14 Stothers and Lee 1992 . PRESENTATION OF STONES IN PREGNANCY Flank pain is the usual presentation with or without haematuria macroscopic or microscopic . Differential diagnoses include placental abruption appendicitis and pyelonephritis to name but a few. WHAT IMAGING STUDY SHOULD BE USED TO ESTABLISH THE DIAGNOSIS OF A URETERIC STONE IN PREGNANCY Exposure of the fetus to ionising radiation can cause fetal malformations malignancies in later life leukaemia and mutagenic effects damage to genes causing inherited disease in the offspring of the fetus . Fetal radiation doses during various procedures are shown in Table 8.1. Radiation doses of 100mGy are very unlikely to have an adverse effect on the fetus Hellawell et al. 2002 . In the United States the National Council on Radiation Protection NCRP has stated Fetal risk is considered to be negligible at 50mGy when compared to the other risks of pregnancy and the risk of malformations is significantly increased above control levels at doses 150mGy NCRP 1997 . The American College of Obstetricians and Gynecologists ACOG has stated X-ray exposure to Table 8.1. Fetal radiation dose after various radiological investigations Procedure Fetal dose mGy mean Risk of inducing fetal cancer up to age 15 years KUB x-ray 1.4 IVU 6 shot 1.7 1 in 10 000 IVU 3 shot CT abdominal 8 CT pelvic 25 Fluoroscopy for 0.4 1 in 42 000 JJ stent insertion CT computed tomography IVU intravenous urogram JJ stent KUB kidney and urinary bladder. 8. URETERIC COLIC IN PREGNANCY 153 .
