Oxytocin antagonists (atosiban) bind competitively
to the oxytocin receptor, thereby inhibiting the
oxytocin-mediated rise of the intracellular calcium
concentration that induces muscle contraction
(Figure 4). According to a current meta-analysis of
nine randomized trials, atosiban is as effective as
betamimetics with respect to the prolongation of
pregnancy and neonatal development (20), and its
side-effect rate is less than 1% (18). No fetal side effects
have been reported; the maternal side effects
are mild (headache, nausea, vomiting). A follow-up
study of infants born after tocolysis with atosiban
revealed no ill effect on their psychosocial and motor
development up to the age of two years (21).