How do combined oral contraceptives (COCs) work in managing menstrual disorders?

How Combined Oral Contraceptives Work in Managing Menstrual Disorders

Combined oral contraceptives (COCs) manage menstrual disorders through three primary mechanisms: suppression of ovulation, thickening of cervical mucus to prevent sperm entry, and thinning of the endometrium to reduce menstrual blood loss. 1

Primary Mechanisms of Action

COCs contain both estrogen and progestin that work synergistically to regulate the menstrual cycle 2:

• Ovulation suppression is the primary mechanism, achieved through inhibition of gonadotropins that normally trigger follicular development and ovulation 1
• Cervical mucus changes increase the difficulty of sperm entry into the uterus 1
• Endometrial alterations reduce the thickness of the uterine lining, which decreases both menstrual blood volume and the likelihood of implantation 1

Specific Applications for Menstrual Disorders

Heavy Menstrual Bleeding

COCs reduce menstrual blood loss by inducing regular shedding of a thinner endometrium. 3 The evidence shows:

• COCs with step-down estrogen and step-up progestogen regimens increase successful treatment (return to menstrual "normality") from 3% with placebo to 12-77% in women with unacceptable heavy menstrual bleeding 3
• The odds ratio for reducing menstrual blood loss is 5.15 (95% CI 3.16 to 8.40) compared to placebo 3
• However, the levonorgestrel-releasing intrauterine system (LNG IUS) is more effective than COCs for reducing menstrual blood loss (OR 0.21,95% CI 0.09 to 0.48) 3

Dysmenorrhea (Menstrual Cramps)

For dysmenorrhea, start with a monophasic low-dose COC containing 30-35 μg ethinyl estradiol combined with levonorgestrel or norgestimate. 4

• COCs reduce dysmenorrhea by decreasing menstrual fluid volume and prostaglandin production, which in turn reduces uterine motility and cramping 5
• Seven consecutive days of hormone pills are necessary to reliably prevent ovulation 4
• The American Academy of Pediatrics recommends the "quick start" approach (starting on the day of the visit) with backup contraception for the first 7 days 4

Irregular Menstrual Bleeding

For irregular periods, 24/4 regimens (24 days of active hormones followed by 4 hormone-free days) provide greater ovulation suppression than standard 21/7 regimens. 6

• Shorter hormone-free intervals result in lower pregnancy rates and significantly greater suppression of ovulation 6
• Unscheduled bleeding is common during the first 3-6 months and often improves with continued use 6
• NSAIDs for 5-7 days during bleeding episodes may help manage breakthrough bleeding 6

Premenstrual Syndrome/PMDD

COCs containing drospirenone may improve overall premenstrual symptoms (SMD -0.41,95% CI -0.59 to -0.24) and functional impairment in productivity, social activities, and relationships 7. However, they also increase withdrawal due to adverse effects (OR 3.41,95% CI 2.01 to 5.78) 7.

Formulations and Dosing

Modern COCs typically contain ≤35 μg of ethinyl estradiol combined with a second, third, or fourth generation progestin. 2

• Low-dose pills (≤35 μg ethinyl estradiol) are recommended as first-line options, with second-generation progestins like levonorgestrel having a safer coagulation profile 4
• COCs are generally used for 21-24 consecutive days, followed by 4-7 hormone-free days 2
• Extended regimens with infrequent or no hormone-free days can be used for specific indications 2

Initiation and Timing

COCs can be started at any time if it is reasonably certain the woman is not pregnant. 2

• If started within the first 5 days of menstrual bleeding, no additional contraceptive protection is needed 2
• If started >5 days since menstrual bleeding started, backup contraception (abstinence or barrier method) is needed for 7 days 2
• Blood pressure should be measured before initiation 2, 4
• A pelvic examination is not required before starting COCs 4

Important Safety Considerations

Women with severe hypertension (systolic ≥160 mm Hg or diastolic ≥100 mm Hg) should not use COCs. 2

Absolute contraindications include 4:

• Migraines with aura or focal neurologic symptoms
• Thromboembolism or thrombophilia
• Ongoing hepatic dysfunction
• Complicated valvular heart disease
• Complications of diabetes (nephropathy, retinopathy, neuropathy, vascular disease)

The risk of venous thromboembolism increases from 1 per 10,000 to 3-4 per 10,000 woman-years with COC use, which remains significantly lower than the 10-20 per 10,000 risk during pregnancy. 4

Common Pitfalls to Avoid

• Do not use COCs to "protect bone health" in functional hypothalamic amenorrhea - COCs inhibit IGF-1 production via first-pass hepatic metabolism, which decreases osteoblastic activity; transdermal estradiol with cyclic progestin is preferred 2
• Do not extend the hormone-free interval beyond 7 days - this increases ovulation risk 4
• Do not assume breakthrough bleeding indicates treatment failure - irregular bleeding typically improves with continued use over 3-6 months 6, 1
• Do not forget that COCs mask the return of spontaneous menstruation - this is particularly important when treating amenorrhea 2

Managing Breakthrough Bleeding

If unscheduled bleeding occurs 2, 1:

• Provide reassurance that it is common, especially during the first 3-6 months 6
• Rule out pregnancy if the bleeding pattern changes abruptly 2
• Consider NSAIDs for 5-7 days during bleeding episodes 2, 6
• For persistent heavy bleeding, a hormone-free interval for 3-4 consecutive days may be considered, but not more than once per month 6
• If bleeding persists and is unacceptable after 3-6 months, counsel on alternative contraceptive methods 2

Additional Health Benefits

Beyond contraception and menstrual disorder management, COC use is associated with 8:

• Substantial decrease in risk of ovarian cancer, endometrial cancer, and colorectal cancer
• Effective treatment for hirsutism and acne vulgaris
• The net effect of additional health effects may result in a slight increase in life expectancy