Incidentally, setting up your hypothetical with a blastocyst is faulty in that the vast majority of abortions are not performed at that stage of gestation.In 2003, the Centers for Disease Control and Prevention (CDC) reported that 26% of abortions in the United States were known to have been obtained at less than 6 weeks' gestation, 18% at 7 weeks, 15% at 8 weeks, 18% at 9 through 10 weeks, 9.7% at 11 through 12 weeks, 6.2% at 13 through 15 weeks, 4.1% at 16 through 20 weeks and 1.4% at more than 21 weeks.
(Strauss, L. T.; Gamble, S. B.; Parker, W. Y.; Cook, D. A.; Zane, S. B.; Hamdan, S.; Centers for Disease Control Prevention (2006). "Abortion surveillance—United States, 2003". Morbidity and Mortality Weekly Report Surveillance Summaries. 55 (SS11): 1–32. PMID 17119534)Update: Source is https://en.wikipedia.org/wiki/Abortion#Gestational_age_and_method. Over 72% of abortions are known to occur after 6 weeks; over 21% of them after the first trimester.