159 Migraine attack incidence in relation to ovulation 7 validity. Additionally, these self-controlled models are more efficient, reducing the need for large control groups. The SCCS model further allows for an overview of the relative risk of migraine attacks across different phases of the menstrual cycle, as it is specifically designed to assess time-dependent risks within individuals. Our data are collected with the Leiden validated headache e-diary with an automated algorithm to evaluate whether each headache day met migraine criteria.17, 19 Diaries were time-locked after 48 hours, reducing recall bias. The large cohort of 554 participants with recordings of 2522 menstrual cycles improves generalizability, and diaries of participants were collected as part of research but also as part of real-world studies as well as standard clinical care, making the results more applicable to the overall migraine population.16 An additional strength of the study is the use of LH-surge urine tests in the WHAT-hormone subgroup to determine the true day of ovulation. In this subgroup, we confirmed that estimating ovulation as the 14th day before menses is reasonably accurate in women with regular menstrual cycles. On average, the calculated ovulation day deviated by only 0.28 days from the actual ovulation day. In conclusion, our study found no increased incidence of migraine attacks (with or without aura) during the ovulatory window in women, but a higher incidence during the follicular phase compared to the luteal phase, potentially linked to lingering effects of perimenstrual estrogen decline. Declaration of interests BWHvdA, DvC, IV, grants from the Dutch Research Council and the Dutch Brain Foundation. SCC and SB have no conflicts of interest. IdB reports independent support from the Dutch Heart Foundation and the Clayco foundation. AMvdB received research grants and/or consultation fees from AbbVie, Amgen/ Novartis, Eli Lilly, Lundbeck, Manistee, Pfizer, Satsuma, Teva, and Tonix. GMT and NP report grants or consultancy support from Abbvie, Lilly, Lundbeck, Novartis, Pfizer, Teva, and independent support from Dutch Research Council, European Community, Dutch Heart Foundation, and Dutch Brain Foundation, Dioraphte, and the Clayco foundation. Funding This study is supported by grants from the Dutch Research Council (849200007) and the Dutch Brain Foundation (HA2017.01.05).
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