Why are there different IVF stimulation protocols?
One of the more common questions we get asked by patients who are preparing to undergo IVF concerns which stimulation protocol is best for them. Many patients have learned about different protocols on the internet or from talking to friends, and they are very curious as to why we would choose one protocol over another.
As part of this discussion, we try to explain the rationale behind stimulation as well as why one protocol may be better than another in their particular situation.
The first thing to understand about ovarian stimulation is that it is a very complex process, and that there are many variables – most related to the patient herself – that can have a significant impact on the ultimate outcome. In a natural cycle, many oocytes begin to develop; the exact number depends on many factors including the patient’s age, her hormonal “status”, and the overall health of her ovaries.
As a rule, older patients have fewer remaining eggs than do younger patients, so they would be expected to develop fewer eggs. Similarly, patients who have abnormal production of the hormones that affect ovulation, such as prolactin, thyroid stimulating hormone, and testosterone, typically do not respond as well to stimulation as they would if their hormone levels were normal.
Finally, patients who have undergone previous ovarian surgery or those who have active ovarian disease, such as ovarian cysts or endometriosis, do not make as many eggs as they otherwise could.
Similarities between IVF protocols
Despite the fact that there are many differences between the more commonly used stimulation protocols, there are also many similarities. For example, almost all modern protocols start with 3-4 weeks of birth control pills (BCPs). Although this may sound counter-intuitive, there are actually several very good reasons for starting stimulation following a cycle of pills.
The eggs in the ovaries of a typical reproductive age woman are in various stages of development. If one were to start stimulation without first taking BCPs, fewer of those eggs would actually develop. It has been shown by several investigators that BCPs actually help the eggs synchronize their development, so that when the pills are stopped and the stimulation medications are begun, more eggs are ready to respond. This results in a greater number of mature oocytes at the time of retrieval, as well as higher fertilization rates when compared to women who undergo stimulation without taking pills first.
In addition to BCPs, there are four other classes of medications that make up the foundation of a stimulation protocol:
- Gonadotropins (or other medications) to cause the eggs to develop
- A gonadotropin releasing hormone (GnRH) analog to prevent premature ovulation
- A medication to cause the eggs to mature, and
- A progesterone to support the uterine lining after embryo transfer
How these medications are administered defines the actual stimulation protocol itself.