When it's your life in the balance, the statistic is 100%.

A few other details, from the Alan Guttmacher Institute (whose link you can also find at the CDC site, in their Reproductive Health section):

• 32 states currently enforce parental consent or notification laws for minors seeking an abortion: AL, AR, AZ, DE, GA, IA, ID, IN, KS, KY, LA, MA, MD, MI, MN, MO, MS, NC, ND, NE, OH, PA, RI, SC, SD, TN, TX, UT, VA,WI, WV, and WY. The Supreme Court ruled that minors must have the alternative of seeking a court order authorizing the procedure. (30)

• 45% of minors who have abortions tell their parents, and 61% undergo the procedure with at least one parent's knowledge. The great majority of parents support their daughter's decision. (31)

This report also breaks down abortion by age, indicating that 19% of all abortions are for women under 20 years old, but not indicating how many of these women are 17-20. Based on other statistics I have seen, I bet that they account for over 75% of the 19%.

You might also be interested in "Trends in Abortion in the United States, 1973-2000", which shows that most abortions are performed for women who are already mothers, hence not the great industry in processing 15-year-old girls that some parties would have us believe.