From the Guidelines
Clomid (clomiphene citrate) typically does not shorten the follicular phase of the menstrual cycle; in fact, it often lengthens it. Clomid works by blocking estrogen receptors in the hypothalamus, which tricks the body into producing more follicle-stimulating hormone (FSH) and luteinizing hormone (LH) 1. This stimulation causes increased follicular development and growth, which generally extends the follicular phase by a few days compared to natural cycles.
The mechanism of action of Clomid is well understood, and its effects on the menstrual cycle have been studied extensively. According to the American College of Obstetricians and Gynecologists (ACOG) guidelines, Clomid is effective in inducing ovulation in women with polycystic ovary syndrome (PCOS) 1. The guidelines recommend treatment with Clomid because of its effectiveness, with about 80 percent of women ovulating and one half of these patients conceiving.
Some key points to consider when using Clomid include:
- The standard Clomid protocol involves taking 50-100mg daily for 5 days, typically starting on cycle days 3-5
- Patients using Clomid should expect their follicular phase to last approximately 12-16 days rather than the typical 10-14 days of a natural cycle
- The lengthening effect is actually beneficial for fertility treatment as it allows for better follicular development and potentially improves the quality of ovulation
- Clomid is recommended as a first-line treatment for ovulation induction in women with PCOS, due to its effectiveness and relatively low risk of side effects 1.
Overall, the use of Clomid in fertility treatment is supported by strong evidence, and its effects on the menstrual cycle are well understood. The lengthening of the follicular phase is a common and expected effect of Clomid treatment, and it is not typically considered a cause for concern.
From the Research
Clomid and Follicular Phase
- The effect of Clomid on the follicular phase is not explicitly stated in terms of shortening in most studies 2, 3, 4, 5.
- However, one study found that Clomid can lengthen the luteal phase in patients with short luteal phases 6.
- Another study compared Clomid-stimulated cycles with human menopausal gonadotropin (hMG)-stimulated cycles and found that the length of the luteal phase was significantly longer in the Clomid-treated group 5.
- A study from 1983 found that Clomid stimulation did not impair luteal phase length or the steroid pattern of oestradiol-17 beta (E2) or progesterone (P) production in spontaneously ovulatory women 3.
Clomid and Ovarian Response
- Clomid can induce ovulation in approximately 70% of treated patients 2.
- The number of retrieved oocytes was similar regardless of the starting dose of gonadotropin (GN) with or without the addition of Clomid 4.
- However, ovarian stimulation with 150 IU gonadotropin in combination with 100 mg Clomid produced more blastocysts 4.
- Clomid may impair fertility through its effects on cervical mucus and in causing various endometrial dysfunctions 2.