Progestin Only Contraceptives

Key Points

• Progestin-only contraceptives are very effective in preventing pregnancy when used correctly and consistently.

• Women with contraindications to estrogen use may safely use POPs.

• Overall, menstrual blood loss is decreased, but bleeding may be unscheduled or irregular.

• Longer-acting formulations may increase perfect-use compliance by decreasing dosing frequency.

• The effect of DMPA on weight gain is variable.

• Although prolonged DMPA use may decrease bone mineral density, this is reversible after discontinuation, and it is not associated with future fractures or osteoporosis.

Mechanism of Action

All progestin-only contraceptive methods act to thicken cervical mucus, thereby inhibiting sperm access to the upper genital tract. They also cause slowing of tubal motility and atrophy of the endometrium. Some methods act to suppress LH and FSH surges, inhibiting ovulation (Zieman et al., 2007).

Progestin-Only Pills

The sole progestin-only pill (POP, often called the "minipill") currently available in the United States contains 35 mg of nor-ethindrone. This pill is taken daily, without a pill-free interval. The main contraceptive effect is through thickening of cervical mucus; ovulation suppression occurs in only 50% of cycles.

Advantages

The POP is very effective in preventing pregnancy when used correctly and consistently. Benefits include decreased menstrual flow and dysmenorrhea, with rapid return to fertility. POPs may be used by women who desire an OC but have a contraindication to estrogen use.

Disadvantages

Main contraceptive effect begins to wane after 22 hours and is gone by 27 hours, so women who are more than 3 hours late with dosing need to use backup contraception. Although overall blood loss is decreased, bleeding or spotting may be irregular or unscheduled. POPs offer no protection against STIs, although infections of the ascending genital tract may be decreased because of thickened cervical mucus (Zieman et al., 2007).

Depot Medroxyprogesterone Acetate (DMPA)

A crystalline suspension, DMPA is injected every 3 months either intramuscularly (150 mg) or subcutaneously (104 mg). Its main contraceptive effect is through ovulation suppression.

Advantages

The convenient dosing schedule of DMPA can increase perfect-use compliance. Advantages include decreased menstrual flow, dysmenorrhea, and elimination of mittelschmerz. DMPA can improve pain from endometriosis and may be used by women with contraindications to estrogen use. It reduces the risk of endometrial and possibly ovarian cancer, as well as significantly decreasing sickle cell crises. DMPA can reduce the number of seizures in women with seizure disorders (Westhoff, 2003). No evidence indicates decreased efficacy in obese women (Goldberg and Grimes, 2007).

Disadvantages

Although overall blood loss is decreased, bleeding and spotting may be irregular or unscheduled. The high amenorrhea rate (>50%) may concern some women. Return to fertility may be delayed (average, 10 months from last injection). Patients often express concerns about weight gain, which is actually quite variable, with no studies showing a consistent impact on weight (Westhoff, 2003) (Level A). Although osteoporosis may develop with prolonged DMPA use because of decreased estradiol levels, bone mineral density (BMD) appears to recover completely after discontinuation, and BMD changes during DMPA therapy have not been linked to fractures or postmenopausal osteoporosis (Goldberg and Grimes, 2007).

Contraceptive Implant

The only contraceptive implant currently available in the United States is Implanon, a single rod 4 cm long and 2 mm wide made of ethylene vinylacetate (EVA) co-polymer and containing 68 mg of time-release etonogestrel. It is placed subdermally by a health care provider and acts primarily by ovulation inhibition. Although FDA approved for 3 years' use, the implant has proven efficacy to at least 4 years (Isly and Edelman, 2007).

Advantages

The contraceptive implant is one of the most effective forms of available contraception, with rapid return to fertility; most women ovulate within 4 weeks of removal (Isly and Edelman, 2007). Benefits include decreased menstrual flow, dysmenorrhea, and elimination of mittelschmerz. The implant can improve pain from endometriosis and may be used by women with contraindication to estrogen use. No effect on BMD is seen.

Disadvantages

The woman must see a health care provider for implant initiation and discontinuation. Although overall blood loss is decreased, bleeding and spotting may be irregular or unscheduled. Amenorrhea may concern some women. The implant provides no protection against STIs and may be associated with headaches or increased acne.

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