Abortion can certainly wait as a topic until much later, but you might want to step up the other part. We had Disney-type movies in school to explain reproduction when I was ten, and my period started about a week later! I naturally thought it was cause-and-effect; you couldn't get your period until you had seen the movie.
My daughters know a little bit. They have the book from American Girl that explains about periods.
When they asked where babies came from, I told them. I didn't go into too much detail.
Next year, before they have "the talk" in fifth grade. I will get them another book about reproduction from the Christian point of view. I got the boy's version for my son. My son learned more about sex from me than the public school, and that is my intent. By the time he was in middle school, he knew about STDs, homosexuality, etc. I just waited until he was starting middle school to educate him.
My daughters are only in 4th grade. They are also going to go to a private Christian middle school. They will not be exposed to as much as my son. However, they will be fully educated in reproduction when they start middle school.