The improved potency of MGA compared to medroxyprogesterone acetate may be due to increased resistance to metabolism of MGA afforded by its C6(7) double bond (medroxyprogesterone acetate being identical to MGA in structure except lacking this feature).The pharmacokinetics of MGA have been reviewed. Chemistry
MGA, also known as 17α-acetoxy-6-dehydro-6-methylprogesterone or as 17α-acetoxy-6-methylpregna-4,6-diene-3,20-dione, is a synthetic pregnane steroid and a derivative of progesterone. It is specifically a derivative of 17α-hydroxyprogesterone with a methyl group at the C6 position, a double bond between the C6 and C7 positions, and an acetate ester at the C17α position. MGA is the C17α acetate ester of megestrol, which, in contrast to MGA, was never marketed. Analogues of MGA include other 17α-hydroxyprogesterone derivatives such as acetomepregenol, anagestone acetate, chlormadinone acetate, cyproterone acetate, hydroxyprogesterone caproate, medroxyprogesterone acetate, and nomegestrol acetate. MGA differs from medroxyprogesterone acetate only by its C6(7) double bond. Close analogues of MGA that were never marketed include cymegesolate (megestrol acetate 3β-cypionate) and megestrol caproate. Synthesis
Chemical syntheses of MGA have been published. History
MGA was synthesized at Syntex in 1959. It was derived from medroxyprogesterone acetate, which had been synthesized at Syntex in 1957. MGA was the third synthetic derivative of progesterone to be developed for use as a medication, following hydroxyprogesterone caproate in 1954 and medroxyprogesterone acetate in 1957.
Pregnancy loss refers to death of the fetus at any time during pregnancy. Pregnancy loss most commonly occurs during the first trimester, when it is referred to as early pregnancy loss. Placenta praevia or vasa praevia refers to the placenta or fetal blood vessels, respectively, covering or being located close to the opening of the uterus. More than half of patients affected by placenta praevia (51.6)% have bleeding before delivery. Vasa praevia occurs in about 0.6 per 1000 pregnancies. Placental abruption involves the separation of the placental lining from the uterus of the mother. It occurs most commonly around 25 weeks of pregnancy. Uterine rupture is when the muscular wall of the uterus tears during childbirth or, less commonly, during pregnancy. Nontubal ectopic pregnancy refers to an ectopic pregnancy that occurs in the ovary, cervix, or intra-abdominal cavity.Other causes of early pregnancy bleeding include the following:

Postcoital bleeding, which is vaginal bleeding after sexual intercourse that can be normal with pregnancy. Iatrogenic causes, or bleeding due to medical treatment or intervention, such as sex steroids, anticoagulants, or intrauterine contraceptive devices. Vaginal or cervical bleeding, which may arise from many causes including fibroids, polyps, warts, tumors, vaginitis, or trauma. Importantly, these causes may co-occur with other causes of early pregnancy bleeding. Lower genitourinary tract bleeding, which may result from a urinary tract infection (UTI), strenuous exercise, or bladder cancer. Pathophysiology
Early pregnancy bleeding is usually from a parental source rather than a fetal one.