Here are some summaries of a few studies about this-
"*Congleton, GK and Calhoun, GC (1993) Post-Abortion Perceptions: A Comparison of Self-Identified Distressed and Non-Distressed Populations, The Int’l Journal of Social Psychiatry 39(4): 255 (Women experiencing postabortion stress were more likely to report a desire to replace the fetus, report depression around the anniversary date or due date, and immediately experience postabortion feelings of loss compared to women reporting relieving/neutral postabortion experiences.)
Vought, Jeanette, Post-Abortion Trauma. 9 steps to Recovery (1991) (53% of women in a postabortion recovery group stated they desired to get pregnant again to compensate for the loss.)
Soderberg H et al (1998) Selection bias in a study on how women experienced induced abortion, Eur J Obstet & Gynecol 77:67 (Swedish researchers at Lund University calculated that, of approximately 33,000 induced abortions in Sweden each year, about 6000 of these women became pregnant again within 12 months, with half of them continuing the pregnancy to term, and another half undergoing another induced abortion.)
Shepard MJ and Bracken MB (1979) Contraception and Repeat Abortion: An Epidemiological Investigation J Biosocial Science 11:289 (In a Connecticut study of abortion and contraceptive practice, it was found that 42% of women repeating abortion had had an abortion within the previous year.)*"