What Are the Causes of a Decidual Cast?

The mucus membrane lining the uterus is known as a decidua once it is implanted with a fertilised egg. A decidual cast forms under the influence of hormones while preparing the uterus for implantation, and it can take on the shape of the uterus. Casts sometimes continue to grow without pregnancy and can cause severe abdominal pain and bleeding.

Depot medroxyprogesterone acetate, or DMPA, is a hormonal contraceptive that has been indicated as a causative factor for the expulsion of a decidual cast. A clinical study published in the November 2007 issue of "The Scientific World Journal" analysed six cases involving women who experienced a decidual cast. The researchers reported that two of the women were using a transdermal contraceptive patch. The physicians placed the women on DMPA and reported no further incidents. However, three of the six had already been prescribed DMPA when their cast was expelled. The researchers concluded that the use of DMPA is not solely the reason for the formation and passing of a decidual cast.

Endometriosis is a condition characterised by the growth of uterine tissue in other areas of the pelvic cavity, which can lead to a variety of complications. Progesterone, a female hormone, is often prescribed to limit the growth of the tissue. An article in the August 2010 issue of "Obstetrics and Gynecology" investigated the relationship between the use of progesterone and the formation of a decidual cast. The physician/author reported that a 16-year-old girl complained of extensive vaginal bleeding and cramping after a procedure to treat endometriosis. The study found that treatment for endometriosis using progesterone can lead to the formation and expulsion of a decidual cast.

Pregnancy can sometimes cause lesions on the uterine walls and resemble the effects of cervical cancer. A report in the January 2005 issue of the "Journal of Lower Genital Tract Disease" described a 28-year-old patient in her 28th week of pregnancy, who complained of extensive bleeding. The physician tested for cervical cancer and a condition known as placenta previa, or early expulsion of the placenta. Upon closer examination, the physician found that the disorder had been caused by the formation of a decidual cast during the term of the pregnancy. Although rare, a decidual cast can be induced by pregnancy.

Ectopic pregnancies occur when the fertilised egg is implanted outside of the uterine lining. A study in the December 1993 issue of "Radiology" investigated the frequency of decidual casts associated with ectopic pregnancies. The researchers evaluated more than 200 cases and found more than 14 per cent were positive for decidual cysts, a precursor of the cast. The study concluded that the formation of decidual cysts was indicative of ectopic pregnancies.