199 General discussion and future perspectives 9 of the different types of contrast (17). It restricts the performance of tubal testing by HSG to women with a high risk for tubal pathology based on their medical history. While some hospitals adhere strictly to this guideline, others have changed their local policy based on the results of the H2Oil study and the results of the subsequent systematic reviews and meta-analyses. Therefore, numerous local policies can be encountered in the Netherlands; some hospitals perform an HSG as a standard test in their fertility work-up and always use either water-based or oil-based contrast, other sites choose their type of contrast based on the results of the H2Oil study or based on the perceived risk for tubal pathology. And some hospitals rarely perform HSG at all. This means that the HSG practice varies greatly throughout the Netherlands which is undesirable. We hope that the results of the studies in this thesis will aid in the formation of new national and international guidelines. MECHANISM Our results on the duration of the fertility enhancing effect of tubal flushing with oil based contrast support the hypothesis of mechanical flushing. In this hypothesis it is thought that oil-based contrast has a greater potential of flushing out pregnancy-hindering debris from the Fallopian tubes, an effect that would lead to a (semi-) permanent increase in fecundity. The duration of the fertility enhancing effect was even longer in the subgroup of patients reporting a higher pain score during HSG, further strengthening this hypothesis. In contrast, the hypothetical mechanism in which the endometrial lining is affected by the use of oil-based contrast would most likely be more temporary as the endometrium renews with every menstrual cycle. Future research should focus on the pressure of infusion of different types of contrast and whether or not a drop of pressure is detectible. This could help to determine whether mechanical flushing is indeed the most likely mechanism of action and whether lubrication of the tubal cilia is involved as well. SAFETY Intravasation The most feared complication of HSG, intravasation, occurs only in a very small percentage of cases based on our literature review (2.7% of HSGs with use of oil-based contrast). In the H2Oil study, intravasation was only reported once in all 1119 HSGs. Radiological techniques have changed drastically over the past five decades, reducing the dosage of iodizing radiation while creating images of higher quality. Fluoroscopy, enabling the physicians and technicians to view live imaging during the procedure, has enabled early diagnosis of intravasation making sure the procedure can be halted before serious consequences appear. It should be noted that in most studies there was no
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