Ovulation disorder in infertility is like planting seeds that cannot grow into seeds, and cannot grow good seedlings, and of course, cannot obtain a good harvest. The most direct treatment for such patients is to use ovulation-promoting drugs to help them ovulate. Among the commonly used ovulation induction prescriptions, sometimes clomiphene, sometimes letrozole, which is better?
Ovulation disorders are the most common cause of female infertility, accounting for 30% of female infertility, and such patients need to induce ovulation to help them become pregnant. At present, clomiphene and letrozole are the most commonly used oral ovulation induction drugs. Which of these two ovulation-promoting drugs is better or worse?
For half a century, clomiphene has been used as a standard first-line drug for ovulation induction, especially PCOS patients to promote ovulation, the ovulation rate is nearly 85%, the cumulative pregnancy rate of 3 to 4 cycles is 35% to 40%, of course, ovulation is not necessarily pregnant, and the general ovulation induction is always a little more patient. Clomiphene is still routinely used in clinical practice, starting from the 3rd to 5th day of the cycle, 50 to 100 mg per day for a total of 5 days.
Letrozole, which came later, was originally just an anti-breast cancer drug, which is mainly to fight the key enzyme of estrogen synthesis - aromatase, so that estrogen levels are reduced, and feedback promotes gonadotropin secretion to promote follicle development. This aromatase inhibitor has been used in the reproductive field to promote ovulation for nearly 20 years and has undergone rapid development. In recent years, a growing body of research has shown that letrozole is no less ovulatory than clomiphene and even better than clomiphene in some patients.
Although both are ovulation-stimulating drugs, the pharmacological mechanism of the two is different: clomiphene is an estrogen mimetic, competing to bind to the central estrogen receptor, causing the central low estrogen signal, feedback to promote the pituitary gland secretion of FSH, play an ovulation-stimulating effect. Letrozole is an external aromatase inhibitor that induces the pituitary gland to secrete FSH by inhibiting the synthesis of estrogen in peripheral tissues, thereby promoting follicle development.
Because the two ovulation-stimulating drugs have different mechanisms of action, they have different effects on follicle development, endometrial growth, follicle excretion, and peripheral blood hormones:
Effects on the endometrium
The anti-estrogenic effect of clomiphene in the endometrium affects the development of the endometrium and the traits of cervical mucus, so the endometrium is thin when clomiphene induces ovulation, and the cervical mucus is less;
Androzole does not specifically compete for the role of estrogen receptors, so it has less effect on the development of the endometrium, which is thick between the natural cycle and the clomiphene cycle.
There are literature reports that the endometrium of the letrozole ovulation induction cycle has a relatively good thickness.
Half-life of the drug
Clomiphene half-life up to 2 weeks, in the body continued to act for 1 to 2 months, and the half-life of bitrozole is about 45 hours, so it can be quickly cleared, so that the level of estradiol rises during the late follicle development, on the one hand, it promotes the growth and development of the endometrium, on the other hand, the negative feedback of estrogen stops FSH secretion in time, and positive feedback induces LH peaks and promotes the discharge of dominant follicles.
Multi-follicle development
Estrogen levels that rise in the late follicular phase of letrozole ovulation inhibit FSH, inhibit multifollicle development, and thus reduce the rate of multiple pregnancies. Clomiphene does not have this effect, its effect on the center is continuous, so there is a risk of continuous development of follicles.
Clinical use should be combined with the above drug mechanisms, comprehensive consideration of the patient's medical history, natural cycle of dominant follicle development, dominant follicle development status, body mass index, whether there is insulin resistance, the number of follicles developed in the previous ovulation induction cycle, speed and ovulation status, the ovulation induction program and dose are individualized.
Cromifen adapts to crowds
1. PCOS patients with pubertal onset, "slim" body type patients, can be the first choice of clomiphene ovulation stimulation therapy, the dose of 50 ~ 100mg / day, after the second cycle can be combined with gonadotropins.
2. Patients with "small follicle syndrome" whose dominant follicles are easy to be discharged early, appropriately select clomiphene to promote ovulation;
Letrozole adapts to the population
1. For obese PCOS patients, it is recommended to use trazole (which can be combined with gonadotropins) to promote ovulation after appropriate weight loss.
2. For patients with follicular flavinylation non-rupture syndrome (follicles do not collapse after 48 hours of HCG or LH peak), letrozole combined with gonadotropin ovulation is recommended.
3. Patients with recurrent miscarriage and uterine problems are recommended to use letrozole in combination with gonadotropin to improve follicle quality and less affect endometrial growth.
4. For ovulation with dominant follicles in the natural cycle, in the process of artificial insemination or pregnancy test, letrozole or gonadotropin, or a combination of the two, is recommended.
5. The "resistance" who has no dominant follicle development after ovulation induction with clomiphene is replaced by trazole combined with gonadotropin;
Therefore, clomiphene and letrozole, two ovulation-promoting drugs, have their own advantages and are suitable for different patients. Which is better or worse? It is still impossible to tell the difference between winning and losing. Clinically, for different patients, different cycles, doctors will choose different ovulation promotion programs and doses, which are all for the best use, to maximize the strengths and avoid the shortcomings. Generally follow the principle of first simple and then complex, first inefficient and then strong, first low cost and then high cost.
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