Simultaneous c-section and umbilical herniorrhaphy
I would consider first seeking the advice of the general surgeon. If the hernia is exposed in the course of an uncomplicated c-section, it may be convienient to perform a combined procedure.
Hernia Repair During C-Section
I see no harm doing a hernia repair at the same time of C-section. However, having said that, you do have a slightly higher rate of recurrence (hernia coming back). I think it is an acceptable rate and since you are already numb and it adds very little time to the surgery, it is feasible to have it done at the same time.
Ventral hernia repair during c-section
In my opinion, a pregnant woman's tissues are not "normal" - they are swollen and do not handle nor behave the same way as they would a few months down the road when you returned to normal. So unless we were dealing with an urgent situation, I would advise caution and waiting for better times. However, I would defer this decision to the surgeon who would be doing the hernia repair.
I think several factors need to be considered here, in addition to the impact on the mother's interaction with the baby, potential complications and increased recovery: The severity of the hernia (including likelihood of INCARCERATION / STRANGULATION (its being caught up in the hole and not being able to fall back in the tummy) which would guide the decision of being able to wait on the repair until a safer time AND the potential use of anti-inflammatory immune system modulating medications which MAY interfere with wound healing (which I am guessing is not the cause because of the pregnancy)
Hernia repair with C-section
You should seek the adivise of a general surgeon. It seems completely readonable to do an umbilical hernia repair at the same time as the C-section as long as there are no complications at the time. I suspect that the tissues would be so loose during the healing that the chance of recurrence may even be less.
Elective surgery and hernia repair
I see many women who develop umbilical hernias around the time of their pregnancy. Umbilical hernias can get larger during pregnancy as the abodmen enlarges, but they rarely pose a problem. The abdominal tissues get very swollen and are not entirely normal immediately after delivery. For that reason alone, I feel that repair of the hernia should be done about 4-6 months after the C-section (not at the same time), once you are down to your normal weight. If you have your hernia repaired at the time of C-section, you run a higher risk of the hernia recurring.
Hernia repair and C-section
C-section is usually not the time to undergo elective procedures, at least not for body-contouring procedures. If the main goal is to repair a true hernia without regard to contour, it might be possible to do this from an intra-abdominal approach as the general surgeon might do for a laparoscopic repair of an inguinal hernia. However, since your tissues and body will be changing drastically as you lose weight and your muscles separate or recover, I wouldn't have any expectations from a contouring point of view.
Hernia repair and c-section
Depending on the circumstances at the time of the c-section and depending on the advice of your general surgeon, it might be reasonable to repair it at that time. Certainly as the tissues shrink, there will be no tension on the repair.