Spontaneous preterm birth is a syndrome caused by infection, inflammation, ischemia, or bleeding and its mechanisms are largely unexplored. Strategies to prevent preterm birth include avoiding risk factors as much as possible and medications such as tocolytics. The main risk factors for preterm birth include a history of preterm birth, shortened cervical length, history of cervical surgery, pre-pregnancy weight loss, poor weight gain during pregnancy, and smoking. Typical tocolytics include ritodrine hydrochloride and magnesium sulfate. The use of continuous infusion of low-dose ritodrine hydrochloride is more frequent in Japan than in the United States (US) and in Europe. Ritodrine hydrochloride has been used in relatively large quantities and on a short-term basis in the US and in Europe. A number of randomized controlled trials (RCTs) have been performed regarding the large quantities and the short-term methods frequently employed in the US and in Europe. They showed that ritodrine hydrochloride had limited efficacy and many side effects, which led to the limited use of ritodrine hydrochloride and beta-stimulants in the US and in Europe. RCTs have not been performed regarding low-dose continuous infusions frequently employed in Japan. Hence, the evidence for this method has not been established. In recent years, the use of ritodrine hydrochloride has decreased substantially in Japan due to the restrictions on the use of beta-stimulants in the United States and in Europe. In addition, progesterone administration has been established in other countries as a method of preventing preterm birth in cases of shortening of the cervical length, and it is being considered in Japan.
The treatment methods prevalent in Japan differ in some aspects from those in Europe and in the US. The lower preterm birth rate in Japan compared to other countries suggests that this difference in treatment methods may be justified. Recent studies have shown that progesterone significantly reduces preterm birth rates. Its indications in Japan should be carefully considered for its appropriate use. More research should be conducted to reduce preterm births in the future.
