I'd say it would depend on the cause of infertility. We turned to IVF after 4years trying naturally - diagnosed with severe endo and PCOS and fell pregnant on 4th round of IVF. I asked the Dr at the time, when it comes to baby number 2 how long should we try before going back to fertility clinic. He recommended that once I stopped breastfeeding to try naturally for 6months, then see him if no success. Our little boy is 4 months old and whilst I would love to breastfeed him as long as possible, I also don't want to leave it too long to start for number , as who knows how long it will take! Ah, wouldn't it be nice if it just happened....