Progesterone is vital for early pre

Progesterone is vital for early pregnancy, and it also plays an important but not fully elucidated role
later in pregnancy. Progesterone treatment in early pregnancy is used for luteal phase support after
assisted reproduction technology to supplement a corpus luteum that may be functioning suboptimally
owing to either ovulation induction or oocyte retrieval [12]. Progesterone may be administered
vaginally as gel or pessaries containing micronised progesterone, which is progesterone
identical to the form produced by the placenta and, therefore, is often referred to as natural progesterone.
The synthetic compound 17-alpha-hydroxyprogesterone caproate (17-OHPC) is administered
intramuscularly. Micronised progesterone may also be administered as oral treatment, but owing to a
first-pass hepatic metabolism if administered orally, parenteral progesterone treatments are more
effective[13]. Vaginal progesterone treatment is often considered more convenient for the patient and
easier to use than intramuscular treatment. In addition, uterine first-pass may increase availability of
progesterone to the myometrium. The most common side-effects to vaginal progesterone treatment
are local irritation and vaginal discharge, whereas intramuscular treatment has side-effects such as
injection site pain, itching, and swelling [13,14].
Accumulating evidence has shown that progesterone supplementation in the second and third
trimester of pregnancy significantly reduces risk of preterm delivery in high-risk singleton pregnancies.
As early as the 1950s, Arpad Csapo [15] suggested that progesterone supplementation could