Patients undergoing Cesarean delivery (C-Section) with a body mass index of 35 or greater (this BMI number is in the obese range) will be given either 2 grams or 4 grams of an antibiotic before surgery. The antibiotic is intended to prevent infection from the surgery.It is unknown what the best dose for large women is for the usual medicine used for this purpose (an antibiotic medicine called cefazolin).Samples of the tissue just under the skin will be biopsied at the time the incision is made and at the time the cut is stitched or stapled closed. A sample of the muscle of the womb will be taken as the womb is stitched closed after the delivery. Blood tests will be done at the start and end of surgery to test the antibiotic level. A blood sample will be taken from the umbilical cord after the baby has been delivered and the umbilical cord has been cut. The umbilical cord blood sample will be tested for the antibiotic level.These tests will be used to find out if the usual dose of medicine is enough or if more medicine is needed to prevent infection in large women undergoing c-sections.

Inclusion Criteria:

1. Age 18 years or above
2. Body mass index (BMI) of 35 or greater at the time of the first obstetric clinic visit
3. Undergoing cesarean delivery

Exclusion Criteria:

1. BMI less than 35.
2. Not undergoing Cesarean delivery.
3. Age less than 18 years.
4. Pre-existing infection.
5. Allergy to cephalosporin medications or a history of an anaphylactic reaction to penicillin.
6. Cesarean delivery being performed under emergent circumstances.