Menstrual cycle be noticed by women practicing fertility awareness. The secretory phase is the final phase of the uterine cycle and it corresponds to the luteal phase of the ovarian cycle. During the secretory phase, the corpus luteum produces progesterone, which plays a vital role in making the endometrium receptive to implantation of the blastocyst and supportive of the early pregnancy, by increasing blood flow and uterine secretions and reducing the contractility of the smooth muscle in the uterus; it also has the side effect of raising the woman's basal body temperature. While some forms of birth control do not affect the
Pharmacokinetics of progesterone and has been found to result in higher serum peak progesterone levels relative to intramuscular oil formulations. In addition, subcutaneous injection of progesterone is considered to be easier, safer (less risk of injection site reactions), and less painful relative to intramuscular injection. The elimination half-life of this formulation is 13 to 18 hours, compared to 20 to 28 hours for intramuscular injection in oil. Progesterone has a very short elimination half-life of about 3 to 90 minutes when given by intravenous injection. A one-year progesterone intrauterine device (IUD) for hormonal birth control was previously available in the United States and