I will admit that there have been a handful of times where, thanks to my oft-malfunctioning reproductive system*, I missed periods when I had been sexually active prior to them. While I was reasonably sure that it was my crappy body acting up and not pregnancy (because we used protection!), the first thing on my mind was abortion. I never wanted to be pregnant. I never wanted to have a baby. I never wanted to be a parent. And I'm glad that I have, my entire life, had the freedom to make that choice.
I have never had "regular" periods. I got my first one on my 10th birthday. I was really too young to understand my body very well, and I thought that I was doing something wrong because I never had the "28 days" cycle. Sometimes it was 30 or more. Sometimes it was 21. It has never been regular, my ENTIRE life. They also have been excruciating, heavy, and nauseating. I didn't get gynecological care when I was a teenager--that wouldn't come until I moved out and dragged myself to the doctor.
Even later in life, when I got on birth control pills, it wasn't regular. It would start up randomly in the middle of the month, even while I was taking the pills. I took Seasonale for a while, but I still had weird sporadic periods. I've got a lot of things wrong down there, but I didn't know that until I took myself to the doctor and got checked out, after I'd moved to New York. I had ovarian cysts, which resulted in the removal of an ovary, a fallopian tube, and a hunk of uterus. I probably have endometriosis, which is hard to diagnose without exploratory surgery. My grandmother had it, and it caused her horrible pain--similar to what I had when I was still having periods--and they found it all over inside her, including on her spine.
Now, I have the Mirena IUD, which has ELIMINATED all of these problems. I don't have a period at ALL. No cramps, no hormone fluctuations, no bleeding, no random misery that happened just whenever my body felt like it. Without it, I may have resorted to hysterectomy to finally get some relief. Mirena exists because of reproductive CHOICE. Any other birth control device (besides surgical sterilization) can be sabotaged, but this is pretty secure. I am really glad that I have this option, without which I would be in a lot of pain. My husband is sterilized, but I like having the backup anyway.