134 Chapter 6 Study procedures Subjects with proven menstrual migraine according to their headache electronic diary (E-diary) data or subjects who have indicated an interest via our web form will receive an information form, an informed consent form and a response leaflet as an invitation to participate in this trial.25 If there is no response within two weeks, a telephone call will be made by a researcher to provide further information. Participants will visit the LHC to determine eligibility. For this purpose initial history (including cardiovascular risk factors and comorbidity) and neurological examination (including also blood pressure measurement) will be performed. A blood sample will also be taken to determine hormone and cholesterol status. If participants give permission 40ml extra blood will be collected and stored for biobanking purposes in the LUMC Biobank Headache (Neurological disorders). The regulations of the LUMC Biobank Headache Collection protocol will be applicable to this biobank collection, registered under BB23.003 (the Netherlands). After the first visit to the LHC participants will start with a baseline period of one month. During the baseline period participants start or continue filling out a daily headache E-diary. After completion of this month, remaining exclusion criteria will be checked (chronic migraine and medication-overuse headache). If a woman is found eligible she will be randomized for either the combined oral contraceptive pill or vitamin E using Castor EDC.28 Before the start of treatment, all participants will take a urine pregnancy test and complete questionnaires (15 minutes). During the baseline visit participants will receive an invitation to fill out an online expectations questionnaire, the Stanford Expectations of Treatment Scale (SETS). This questionnaire will be used to help assess expectancy effects of both interventions. For participants whom already registered one month of E-diary data prior to the inclusion visit, additional baseline measurements are not needed. The questionnaires filled out during this period serve as baseline measurements for these participants. The baseline period is followed by the intervention period of three months. Participants will start with either ethinylestradiol/levonorgestrel 30/150μg or vitamin E 400IU once daily. We will actively implement strategies to enhance participant retention in this study. This proactive approach involves monthly contact with patients throughout the treatment period. Regular communication aims to strengthen the engagement and commitment of participants to the study, thereby minimizing the likelihood of attrition. Participants on oral contraceptives will be strongly encouraged to take the medication without a stop week if mild spotting or break through bleeding occurs. In case of long lasting or unacceptable break through bleedings, women are allowed to skip the combined oral contraceptive pill for 7 days, during which they
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