Wean first. I got pregnant while breastfeeding my 19 month old. Miscarried at 7 weeks. Gynea advised that half the women she treats who breast fed while trying to concieve ended up like me. breastfeeding taxes the body and the egg released may not be in optimum condition. Your hormones will also be supporting both the sibling and the little one inside. The risk no matter how small is real. Give your unborn child the best shot in life. Her advise to me was to wean, wait at least 1 normal cycle to ensure that your hormones are ok then try. dont't make the same mistake as me. I really regret not knowing this earlier. You can also google breastfeeding + miscarriage to read more.