I am assuming you are getting bilateral prophylactic mastectomies. While it is possible to do the reconstruction and abdominoplasty simultaneously, you should have your surgeons assess the risk of the procedures. From a healing point of view, the incisions and undermining necessary might reduce blood flow to certain areas of the breast and abdomen such that healing may be a factor. Total blood loss from combined procedures may also reduce oxygen-carrying capacity and thus hinder healing and may also place you at risk for needing blood transfusions you might ordinarily not need. In addition, tension placed on the abdomen often will change the position of the inframammary fold that is critical in assessing position of the implants.
Finally, while bilateral silicone implants for bilateral prophylactic mastectomy reconstruction is a sound option, there may be a significant risk of hardening or intolerance to the implants that might make autologous reconstruction a better long-term solution in case of implant failure. Your plastic surgeon should factor this into his/her decision about reconstructive options. Think carefully about choices so you and your surgeon do not get painted into a corner.



