The purpose of this study is to determine what dose of medication administered through a combined spinal epidural (CSE) provides the optimal pain relief with the minimal amount of side effects. The 3 doses studied here (1.25, 1.66 and 2.5mg) are routinely use on the labor floor (depending on the physician preference) but the idea is to quantify safety, efficacy and side effects for each of these doses.

A combined spinal epidural (CSE), which is the investigators' customary method of providing pain relief during your labor, is the identification of the epidural space in your lower back with a needle, followed by passing a thinner and longer needle through the first needle. This second needle will enter the patient's "spinal" (intrathecal) space by passing through the dura (thin covering separating the epidural space from the spinal space). The spinal (intrathecal) space is identified by flow of spinal fluid. The dura is the envelope around the spinal cord and the intrathecal space which is filled with spinal fluid. Medication will be injected at once into the spinal space, the thinner needle removed and a fine tube (catheter) will be threaded through the first needle into the epidural space. This catheter is in the epidural space and medication can be given through this catheter later on (hence the term combined) if needed. This study is a comparison of three different dosages (1.25mg, 1.66mg and 2.5 mg) of the local anesthetic (Bupivacaine) that we frequently use in the spinal, mixed with 20 mcg of Fentanyl (also routinely used in standard of care practice), and of its effects on the patient's blood pressure (risk of maternal's drop of the blood pressure with possible bad effects on the blood flow to the baby), on the patient's baby's heart rate (risk of slowing down of the baby heart rate as a consequence of decreased blood flow to the baby), and the patient's pain relief (higher dose of medications are usually more effective for maternal pain relief but have side effects that can be bad for the mother and the baby). The doses of Bupivacaine the investigator routinely use on the labor and delivery floor go from 1.25 to 2.5 mg depending on clinician preferences. These doses are considered standard of care in the literature.

Inclusion Criteria:

• ASA (American Society of Anesthesiologists Physical status) 1-2 parturients at term requesting labor analgesia
• between 37 and 42 weeks gestational age
• maternal age of 18 years or greater

Exclusion Criteria:

• Parturients with pre-eclampsia
• History of pregnancy induced hypertension
• Patients in whom a spinal anesthetic is contraindicated (e.g. coagulopathy, local infection) or those in whom a CSE cannot be performed
• Patients with non reassuring fetal heart rate tracings prior to placement of the CSE

60 minutes