Nexplanon and Ovarian Function: What Happens to Eggs and Weight Concerns
The eggs (follicles) that would have been ovulated during Nexplanon use remain in the ovaries in a dormant state and are preserved for future use—they are not "lost" or depleted, and ovulation typically resumes within 3-4 weeks after removal. 1, 2 Regarding weight gain, while baseline weight monitoring is recommended by CDC guidelines, the evidence does not establish Nexplanon as a definitive cause of significant weight gain. 3
What Happens to the Eggs During Suppression
Mechanism of Ovulation Suppression
- Nexplanon (etonogestrel implant) primarily works by suppressing ovulation through prevention of the mid-cycle luteinizing hormone (LH) peak. 4, 1
- The implant initially suppresses follicular development and estradiol production, though ovarian activity slowly increases after 6 months of use. 1
- Despite this gradual increase in follicular activity, endogenous progesterone levels remain in the subovulatory range for more than 3 years in most users, maintaining contraceptive protection. 1
Fate of Unsuppressed Follicles
- The follicles that would have matured and ovulated simply remain in the ovarian reserve—they do not disappear or get "used up." 2
- Ultrasound studies demonstrate that ovulation occurs in less than 5% of users even after 30 months of use, confirming sustained suppression. 1
- In a 3-year study, the first ovulation with Implanon (predecessor to Nexplanon) was not observed until after 30 months, indicating robust and consistent ovulation inhibition. 2
Rapid Return to Fertility
- Ovulation resumes promptly after implant removal, typically within 3-4 weeks, confirming that the ovarian reserve is preserved and not depleted. 1, 2
- Etonogestrel becomes undetectable within 1 week of removal, allowing rapid restoration of normal ovarian function. 1
- This quick return to fertility demonstrates that the suppressed follicles were simply dormant, not destroyed or permanently affected. 2
Weight Gain Concerns with Nexplanon
Guideline Recommendations on Weight Monitoring
- CDC guidelines recommend measuring baseline weight and BMI before implant insertion, primarily for monitoring changes over time and counseling women concerned about weight changes, not because weight gain is an established side effect. 3
- The recommendation explicitly states that screening for obesity is not necessary for safe initiation, as obese women can safely use implants. 3
Evidence on Weight and Implant Efficacy
- Etonogestrel levels remain comparable across a wide BMI range, with studies showing no significant difference in drug levels between normal weight and obese users (p=0.1). 5
- The only exception is that women weighing less than 50 kg may have approximately 40% higher etonogestrel levels, but this does not translate to increased side effects. 1
- The implant maintains contraceptive efficacy regardless of body weight, with effectiveness independent of BMI through 3 years of use. 5
Clinical Context
- The most common adverse reaction reported with Nexplanon is change in menstrual bleeding patterns, not weight gain. 4
- In clinical trials summarized in pediatric guidelines, bleeding patterns were the primary concern leading to early discontinuation, with no emphasis on weight gain as a major issue. 3
Important Caveat
The baseline weight measurement recommendation exists to help counsel women who perceive weight changes to be associated with their contraceptive method, not because weight gain is a documented or common side effect. 3 This distinction is critical for patient counseling—the monitoring is for reassurance and documentation, not because significant weight gain is expected.