**6. Administration of progesterone: intramuscular administration of progesterone**

Intramuscular administration of 17-alpha hydroxyprogesterone is considered to be effective in preventing preterm delivery in singleton pregnancies with a positive history of preterm delivery. Regarding twin pregnancies, intramuscular administration of 17-alpha hydroxyprogesterone 500 mg twice weekly can approximately four-fold reduction in delivery before 32 weeks gestation (RR 3.78, p < 0.001) but cannot reduce the risk of delivery before 37 weeks gestation (RR 1.06, 95% CI 0.75, 1.51) [36–42].

However, no benefit was seen in neonatal-perinatal outcomes when intramuscular progesterone was compared with sham treatment. Thus, at present intramuscular progesterone is not recommended in twin pregnancies, although it would be of particular interest to further clarify its administration in a high-risk group pregnant.
