1. Singh S. Wulf D. Hussain R. Bankole A. Sedgh G. Abortion Worldwide: A Decade of Uneven Progress http://www.guttmacher.org/pubs/Abortion-Worldwide.pdf
2. The “problem” of repeat abortions;Tietze;Fam Plann Perspect,1974
3. The mathematics of repeat abortion: explaining the increase;Tietze;Stud Fam Plann,1978
4. Jones R.K. Singh S. Finer L.B. Frohwirth L.F. Repeat Abortion in the United States. Occasional Report No. 29 http://www.guttmacher.org/pubs/2006/11/21/or29.pdf
5. Age, parity, history of abortion and contraceptive choices affect the risk of repeat abortion;Heikinheimo;Contraception,2008