There are no absolutely guidelines. An abortion, be it in first pregnancy or later pregnancy, may cause problems. It depends on many factors including at what period of gestation one is going for abortion, what is the indication for abortion, what is the general fertility status of the couple, etc. Abortion may cause bleeding, and in few cases where medical management fails and surgical managememt needs to be done, sometimes problem in conceiving again may happen. It is better to go for supervised medical abortion by an eligible doctor for an indication which you and your partner think mandates abortion.