The present invention is related to the use of pyrrolidine esters of formula (I) for the treatment and / or prevention of premature labor, premature birth and dysmenorrhea. In particular, the present invention is related to the use of pyrrolidine esters of formula (I) to modulate, notably to antagonise the oxytocin receptor. The present invention is furthermore related to novel pyrrolidine esters. X is selected from the group consisting of CR6R7, NOR6, NNR6R7; R is selected from the group comprising or consisting of C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, saturated or unsaturated 3-8-membered cycloalkyl which may contain 1 to 3 heteroatoms selected of N, O, S, aryl, heteroaryl, C1-C6-alkyl aryl, C1-C6-alkyl heteroaryl. R1 is selected from the group comprising or consisting of C1-C6-alkyl, C2-C6-alkenyl, C2-C6-alkynyl, aryl, heteroaryl, 3-8-membered cycloalkyl, acyl, C1-C6-alkyl aryl, C1-C6-alkyl heteroaryl, said cycloalkyl or aryl or heteroaryl groups may be fused with 1-2 further cycloalkyl or aryl or heteroaryl group.