Randomization
Upon request for neuraxial labor analgesia, subjects were
randomly assigned to receive epidural or CSE analgesia.
A statistician (J. B.) created randomization tables for 4 subgroups
of 200 women in blocks of 20 using Microsoft Excel’s
random number generator. Specifically, for each block of 20,
random numbers between 0 and 1 were assigned to the integers
1 to 20, then sorted so that the integers with the smallest
10 random numbers were assigned to epidural group
and the largest 10 random numbers to the CSE group. This
was repeated with a new seed for each block and performed
for each of the 4 subgroups. The subgroups were designed
to stratify for parity (nulliparous versus parous) and induction
versus spontaneous labor. Hence, the 4 subgroups were
(a) nulliparous women in spontaneous labor, (b) nulliparous
women in induced labor, (c) parous women in spontaneous
labor, and (d) parous women in induced labor.
The patient, attending nurse, and obstetrician were
blinded to group assignment. In some, but not all instances,
the individual collecting data was blinded to group assignment.
After providing consent, patients were assigned to
the next available study number in 1 of the 4 subgroups by
opening the next sequential sealed, opaque envelope. The
anesthesiologist performing the block opened the envelope
at the time of request for epidural analgesia.