I missed mine for a full year when I lost weight and started exercising. (I got down to 145 lbs, so I wasn't "underweight", but realized that's too thin for me). Anyway, I was in college and grad school and I didn't think much of it at the time - that was almost 20 years ago. Looking back on it, I wish I'd consulted with a doctor about it because the effect on bone health is not good at all. It didn't have any apparent effect on my ability to later have a kid, etc.