A non-invasive hemoglobin monitor will be used during cesarean delivery and the values obtained will be compared to values obtained from traditional blood draw.

Obstetric hemorrhage remains the leading cause of maternal death worldwide (2). The most common culprits are uterine atony, placental disorders, and delivery trauma. Current detection and management of hemorrhage is heavily based on clinical judgment and laboratory results. Interventions such as fluid resuscitation and blood transfusion are often initiated after a significant hemorrhage has already taken place. Early detection and treatment of this potentially life threatening obstetric complication is of upmost importance in the field of obstetrics. Traditional methods for assessing hemoglobin levels involve collecting the patient's blood and sending it to the laboratory for analysis via complete blood count (CBC). This involves a delay and often patients are continuing to hemorrhage while the CBC is being processed. Novel technology has recently been approved by the FDA, which can continuously assess hemoglobin levels via a non-invasive monitor. This device works as a pulse oximeter, which is placed on the index finger and uses infrared technology to estimate hemoglobin levels (1). Despite its validation and use in many patient populations such as trauma, neurosurgery and orthopedic surgery, data is lacking in an obstetric population. The investigator's hypothesis is that this device will enable clinicians detect hemorrhage early and initiate resuscitation such as fluid and/or blood transfusion before significant hemorrhage has taken place. This study will be a proof of concept prospective cohort study, in which the investigators will attempt to detect the association between intra-operative and postoperative continuous non-invasive hemoglobin monitoring and postpartum decrease in hemoglobin.

Women undergoing primary cesarean delivery after failed induction of labor or repeat cesarean delivery after failed TOLAC (trial of labor after cesarean delivery), will be eligible for participation in this study. Prior to cesarean, all patients will have a CBC drawn. Masimo non-invasive hemoglobin monitor will be placed on their finger during delivery and remain in place until discharge from the recovery room. All patients will have CBC drawn on post operative day 1, as is the standard of care at our institution. Based on the drop in hemoglobin from pre-op to post-op day 1, patients will be separated into quartiles. The quartile with the highest drop in hemoglobin will be the "cases" and compared to the remainder of the quartiles or "controls." In addition, values obtained from the non-invasive monitor will be compared to those obtained from CBC.

Inclusion Criteria:

• Pregnant women undergoing primary cesarean delivery after failed induction of labor, or repeat cesarean delivery after failed TOLAC (trial of labor after cesarean)
• Pregnant women between the ages of 18-50

Exclusion Criteria:

• Patient who are not pregnant
• Patients unwilling or unable to provide consent
• Patients under the age of 18
• Patients who are incarcerated

through study completion, an average of 1 year

Since every patient will have the device placed during delivery, there will be no masking. However, the actual values obtained from the monitor will be masked.