McRoberts’ maneuver (acute flexion of the hips
while the woman is on supine position) straightens
the lumbosacral angle, allowing descent of the
posterior shoulder. The maternal pelvis is perpendicular
to the direction of the maternal expulsive
forces. Gonik et al.,50 using computer models,
showed that with lithotomy positioning both
endogenous and exogenous delivery forces were associated
with stretching of the brachial plexus during
shoulder dystocia (the percentage of brachial
plexus nerve stretch was 15.7% vs. 14.0%, respectively).
McRoberts’ positioning resulted in 53% less
brachial plexus stretch (6.6%).
Directed suprapubic pressure (continuous or
“rocking” pressure on the posterior aspect of the anterior
shoulder) facilitates adduction of the shoulders,
a reduction of the bisacromial diameter and
rotation to an oblique position