As disclosed herein, novel compositions including steroid hormones, such as trimegestone (TMG) and progesterone (P4), provide treatments for term and preterm labor with significant effects on the delay of delivery. Delay and block of delivery occurs when both P4 and TMG are administered late in gestation in pregnant rat and guinea pig animal models. TMG exhibits remarkable drug efficacy, achieving the same inhibition as P4, but at much lower doses. These hereto unknown effects of TMG on the processes of cervical ripening and uterine contraction provide a novel approach for extending pregnancy term, including reducing a likelihood of preterm and/or term labor, along with improved methods of administration. Other diseases and/or conditions may be treated with TMG, such as dysmenorrhea or luteal insufficiency for sustaining pregnancy.