91 Safety of HSG with oil-based contrast medium 5 no fluoroscopy guidance (19% versus 79%). With the use of fluoroscopy guidance during HSG, no serious consequences of oil embolisms occurred. The frequency of infection with the use of oil-based contrast was 0.90% (20 studies, 95% CI 0.47–1.50), compared with 1.9% (four studies, 95% CI 0.27–4.60) with the use of water-based contrast. One case of non-infection-related mortality after an HSG, most likely due to an anaphylactic reaction, was reported in 1947. There were 85 reports of oil remnants after an HSG. Half of the cases were diagnosed within 2 weeks of the procedure. Furthermore, there were 41 reports of lipogranuloma formation. Women with subclinical hypothyroidism seem more likely to develop hypothyroidism after an HSG with oil-based contrast (35.7% versus 0–2.2% in euthyroid women), however this is based on only 28 and 202 women, respectively (56, 73, 101). Results on the effect on thyroid function of the offspring are contradictory; a Japanese study showed abnormal congenital thyroid screening in 2.4% whereas a Dutch study did not show any abnormalities (94, 108). This is the first systematic review on the safety of HSG with oil-based contrast that includes all study types. Another strength of this systematic review is that no restriction on language or publication date was applied. However, the systematic review has limitations. First, the quality of the included studies was moderate to low. This is attributable to the design and the publication year of the included studies. In most of the studies the primary outcome was pregnancy-related. Complications were often reported as secondary outcomes. Second, the development of fluoroscopy guidance during HSG has helped clinicians to diagnose intravasation and oil embolisms, leading to timely termination of the HSG procedure. This development is suggested as the reason for the increase in reported cases of intravasation and oil embolisms, however as mentioned previously, the percentage of symptomatic oil embolisms has therefore drastically decreased. Oil embolisms, also known as fat embolisms, have not only been reported in the gynaecological literature. Bone marrow fat embolisms occur in 11–19% of trauma or orthopaedic surgery patients (129). Fat embolisms may cause a fat embolism syndrome, with clinical symptoms varying from right heart failure and cardiovascular collapse to hypoxemia, pyrexia, petechial rash and neurological symptoms (129) . When reaching the lungs, the fatty substance mixes with the locally secreted lipase. Free fatty acids are released, causing inflammation to the pulmonary microvasculature and leading to a shock lung-like or acute respiratory distress syndrome-like syndrome (130). Suggested
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