Our objective was to compare the effectiveness and safety of atosiban and ritodrine, in pregnancies obtained by intracytoplasmic sperm injection (ICSI) undergoing cervical cerclage. Data from a prospective study were compared with those from a retrospective study. Sixteen ICSI pregnant women, 20-24 weeks' gestation and maternal age >18 years, received atosiban (bolus dose 6.75 mg i.v., followed by 300 microg/min i.v. for 3 h and 100 microg/min i.v. for 45 h). Cervical cerclage was performed 3 h after starting atosiban. The control group (group B) of 16 ICSI pregnant women were matched and received ritodrine hydrochloride (100-350 microg/min) for 48 h. Cervical cerclage was performed after 24 h. Pre-term rupture of membranes occurred within 48 h of cervical cerclage in one woman receiving atosiban and in four women receiving ritodrine. There was no significant difference in terms of pregnancies not delivered at 48 h (short-term tocolysis) and at 7 days (long-term tocolysis). However, there was a significantly higher incidence of maternal tachycardia with ritodrine compared with atosiban (p < 0.001). The mean gestational age at delivery was significantly higher for atosiban compared with ritodrine (36 vs 33 weeks; p < 0.001). The neonatal outcome was poorer for ritodrine than atosiban, as there were very low birth weight infants (p = 0.008), resulting in lower Apgar scores (p = 0.005) and there were more neonates requiring a long stay in the neonatal intensive care unit (p = 0.005). We conclude that atosiban is associated with a significantly lower incidence of maternal tachycardia and improved neonatal outcome compared with ritodrine.