Clomid – clomiphene citrate – is a commonly prescribed fertility medication, but one possible side effect of the drug is thinning of the endometrium.
Fertility specialists commonly prescribe Clomid as a first-line fertility treatment. The drug works as an anti-estrogen to stimulate ovulation in women who suffer ovulatory dysfunction.
During a normal menstrual cycle, estrogen works to thicken the uterine lining to prepare for implantation of the fertilized embryo. Reproductive endocrinologists prefer the endometrial lining to be at least 8mm thick during infertility treatment. The anti-estrogenic effect of Clomid can prevent endometrium thickening in 25-30% of women.
Endometrial thinning occurs because the drug contains two geometric isomers. One of the isomers clears the body within a week, but the second isomer lingers much longer, remaining in the system up to several weeks. When Clomid is administered for multiple cycles – 3 or more – it allows the second isomer to build causing thinning of the endometrial lining.Some patients experience endometrial thinning even earlier in the treatment cycle.
Multiple studies have shown both implantation rates and ongoing pregnancy rates are reduced when endometrial thickness is less than 7mm. A thin endometrium is also associated with a greater risk of miscarriage.
During fertility treatment, an endometrial thickness of at least 8mm is desired. Since clinical pregnancy and ongoing pregnancy rates are closely correlated with endometrial thickness, reproductive endocrinologists use ultrasound to monitor uterine lining thickness in patients taking Clomid.
If you experience thinning of the endometrial lining while taking Clomid, your fertility specialist may discontinue the drug for a 6-week period to allow it to completely clear from your system.
Your doctor may also discontinue Clomid in favor of an alternate therapy. Femara – letrozole– an aromatase inhibitor that is effectively used to stimulate ovulation in some women – or Tamoxifen, a selective estrogen receptor modulator, may be substituted for Clomid.