Our decision was a combination of infertility factors and our age - i turned 40 in may. If not for those 2 factors, we would've waited longer to start trying for #2. As it was, i weaned DS at 6 mths, and we started IVF again when he was 8 mths. We had 2 failed cycles and than a natural miracle!! So there will be a 20 mth gap between them - a little less than i would've liked, but we just didn't want to wait too long in case it took 18 months again. Good luck!!!