"An abortion when the baby is fully formed" would be any abortion at 8 weeks or later. Eight weeks marks the transition from embryo to fetus -- a developmental milestone in that every essential structure of the human body is now present. There is nothing for the fetus to do now but mature.
Learn more about prenatal development here.
Mind you, the embryo doesn't just abruptly coalesce into a fetus at 8 weeks. Development has been going on since Day 1. The heart has been beating for weeks. The brain has formed into forebrain, midbrain, and hindbrain, and has already begun to produce measurable brain waves. The kidneys have been producing urine for a week. The tiny chest even sports nipples.
The most recent data by the Alan Guttmacher Institute indicates that of 1.21 million abortions done in the United States in 2005. AGI lumps 8 week abortions on fully-formed fetuses in with abortions at 7 weeks or less, which destroy embryos. The CDC does this as well, as we can see in this chart in their 2005 Abortion Surveillance Summary. We have to go to another chart entirely to see what percent of abortions before 9 weeks are done on 6 and 7 week embryos, and what percent on 8 week, fully-formed fetuses. It shows that 30.4% are done on 6-week or younger embryos, and 17.1% on 7-week embryos, for a total of 47.5% of abortions, or less than half, being performed on embryos, and 52.5% being performed to destroy approximately 635,000 fully-formed fetuses.
You can click here to see the results of these abortions.