Progestin Contraceptive Injections
Depot medroxyprogesterone acetate (DMPA) is a long-acting injectable formulation of medroxyprogesterone acetate in a crystalline suspension. Pregnancy rates in the first year are 0.2% with perfect use and about 6% with typical use (ie, delays between injections).
DMPA may be given as an IM (150 mg) or sc injection (104 mg) q 3 mo. The injection site is not to be massaged because doing so may increase the rate of absorption. Effective contraceptive hormonal serum levels are usually attained as early as 24 h after injection and are maintained for at least 14 wk although levels may remain effective for up to 16 wk. If the interval between injections is > 16 wk, a pregnancy test should be done to rule out pregnancy before the next injection is given. DMPA may be started immediately (a quick-start protocol) if DMPA is given within the first 5 to 7 days of the menstrual cycle. If it is not started during this time frame, a backup contraceptive method should be used concurrently for 7 days. DMPA may also be given immediately after a spontaneous or induced abortion or immediately postpartum regardless of breastfeeding status.
The most common adverse effect of DMPA is irregular vaginal bleeding. In the 3 mo after the first DMPA injection, about 30% of women have amenorrhea. Another 30% have spotting or irregular bleeding (usually light) > 11 days/mo. Despite these bleeding abnormalities, anemia does not usually result. With continued use, bleeding tends to decrease. After 2 yr, about 70% of DMPA users have amenorrhea. Because DMPA has a long duration of action, ovulation may be delayed for up to 18 mo after the last injection. After ovulation occurs, fertility is usually rapidly restored.
Women typically gain 1.5 to 4 kg during the first year of DMPA use and continue to gain weight thereafter. Because changes in appetite rather than metabolism are thought to be responsible, women who want to take DMPA are usually advised to limit caloric intake and increase energy expenditure.
Headache is a common reason for stopping DMPA, but severity tends to decrease over time. Most women using DMPA do not have headaches, and preexisting tension headaches and migraines usually do not worsen.
Mild, reversible deterioration of glucose tolerance and lipid profile may occur. Although bone mineral density may decrease when estrogen levels are low, there is no evidence of increased fracture risk, and bone scanning is not recommended for women who use DMPA. Adolescent and young women who use DMPA, like those who do not, should consume 1500 mg of Ca and 400 units of vitamin D daily; supplements should be taken if necessary.
Unlike combination oral contraceptives, DMPA does not increase the risk of hypertension. Progestins are not believed to increase the risk of thromboembolism; however, some evidence suggests that use of DMPA may double the risk of thromboembolism. However, this association is not well-established, and DMPA is currently considered safe for women with contraindications to estrogen use.
DMPA does not appear to increase the risk of breast, ovarian, or invasive cervical cancer. DMPA reduces the risk of endometrial cancer, pelvic inflammatory disease, and iron deficiency anemia. Some evidence suggests DMPA may reduce the incidence of painful crisis in women with sickle cell disease.
DMPA may be an appropriate contraceptive option for women with a seizure disorder.
Other contraceptive injections are available elsewhere in the world.