Randomization: Once enrolled in the study, all of the subjects were randomly assigned to one of two groups using the sealed opaque envelopes technique. A nasal cannula was attached to all subjects and was connected to a flowmeter covered by a metal foil so that the managing obstetricians were not aware which group the particular subject belongs to. The Oxygen Group participants received 100% oxygen at 2 litters/minute starting at least 30 minutes before delivery. The Control Group participants had their nasal cannula still attached to a flowmeter that was turned off. Nasal cannula was disconnected from participants after delivery.