As anyone who has had their period will know, menstrual cycles are a complicated business. Not only can cycles be unpredictable—even the best period-monitoring app in the world can’t seem to tell me when I’m ovulating—they can also affect a person’s orgasm.

I often have sex on my period and am a big believer in having sex as often as possible, mainly because it makes my body feel so much better (the healing powers and painkilling properties of orgasms). But one thing I’ve noticed is that my orgasms change in intensity and sensation throughout my menstrual cycle. While one week, I might experience intense and full-body orgasms, the next week, the climax could be altogether duller and muted.

MORE: 3 Science-Proven Ways to Have More Orgasms

According to Psychology Today, several studies have determined that a person’s menstrual cycle has an automatic effect on their orgasms. As the publication notes, the University of Virginia in Charlottesville conducted a survey charting 115 women between the ages of 23 and 45. “[T]he women reported significantly more interest in sex and greater satisfaction from orgasm at mid-cycle.”

Similarly, Dutch researchers found that “genital blood flow increased the most around the time of ovulation,” leading to stronger orgasms. As Psychology Today concludes, there’s a definite link between women’s orgasms and their menstrual cycles.

Redbook spoke to Dr. Jamie Knopman, who said, “The cervix also changes position around the time of ovulation—its position becomes more ‘comfortable’ when you are ovulating, making intercourse less uncomfortable.” Basically, changes happening in your body linked to your menstrual cycle could be making sex better and increasing the chances of having an orgasm.

The creators behind the period-tracking app Glow shared their research with SheKnows, taking “7.6 million sexual encounters into consideration.” According to their findings, “orgasm potential is directly related to when you get your period.” While the exact timing of the perfect orgasm might vary from person to person, Glow’s research suggests most women will be at their horniest one week before their period. And the scientific reason for this? “Because while a woman’s testosterone levels drop then, her libido increases because her uterine lining is thickening.” So the science might not sound sexy, but the changes in testosterone levels make sense.

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For me, my orgasms vary massively depending on how my body is feeling, altered by both my menstrual cycle and my chronic illness. Consistently, my orgasms feel less intense in the week leading up to my period, despite sex still being enjoyable. When I reach the climax, during this time, my orgasms often feel zapped of intensity or they fail to send pleasure in all of the directions it’s meant to go. Conversely, during and right after my period, my orgasms usually feel fuller, more powerful and filled with twanging muscle spasms. That there’s a reason for these changes and a pattern that develops each month is reassuring.

Originally posted on SheKnows