145 VR for pain relief in HSG 6 when they had received high-pain cues, compared to participants receiving low-pain cues (20). However, the mean overall pain scores found in our study (VAS 5.0 in the intervention group and 4.9 in the control group) are in line with pain scores found as a secondary outcome in a previous study (VAS 5.0 median) (9). This secondary analysis additionally found that women receiving oil-based contrast had a higher ongoing pregnancy rate if they experienced moderate to severe pain during HSG than when they experienced mild pain (9). This difference was not seen in women who received water-based contrast during HSG. The hypothesis for this pregnancy enhancing effect is that oil-based contrast has a greater potential to flush away pregnancy hindering debris because of its chemical or physical characteristics. The contrast fluid is thought to create a pressure build-up behind the debris, causing pain, until the debris comes loose and the pressure releases. More pain anticipated prior to the procedure either might have influenced both the intervention and the control group, or might not have influenced the pain scores at all. In our study, we did not include ongoing pregnancy rate as a secondary outcome. Therefore, we could not compare the reported pain scores to pregnancy rates. It is known that tubal blockage causes a higher level of pain during HSG than bilateral tubal patency (21). In our study, we saw a non-significant difference in the prevalence of bilateral tubal patency between the intervention- and the control group (75.4% versus 80.0%, respectively. P=0.481). Bilateral tubal blockage was diagnosed in only one woman in the control group and two women in the intervention group. In addition, we found that tubal patency did not significantly influence the reported (average) pain scores. This is contrary to the findings by Szymusik et al. where a significant difference was reported in VAS scores during contrast instillation by women with any abnormality in tubal patency, compared to women with bilateral tubal patency (VAS-score of 7.30 in women with abnormal tubal patency versus 5.80 in women with bilateral tubal patency, p<0.001) (21). For our study, we chose to turn off the sound of the VR application. We deemed it important that the caregiver was able to communicate with the patient and explain different steps of the HSG procedure. This might have influenced the level of immersion of the patient, and thereby the pain reduction properties of VR. Previous research demonstrated that the highest pain tolerance was reported by patients exposed to both visual VR and its supplementary sound, compared to visual VR alone (22). Won et al. stated the five criteria for successful VR in their paediatric study (23). These five criteria comprised presence (subjective feeling that the user is inside the VR environment), interactivity (involvement of the user into the VR environment, e.g. by incorporating tracked body movements), social interactions (a VR environment can offer an alternative platform to build relationships), customization (adjusting the VR environment to the patient preferences) and embodiment (user is embodied in the VR environment through
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