Stimulating the ovaries with injections of FSH
By prescribing a carefully controlled dose of FSH and other hormones and monitoring their effects, your doctor aims to bring to maturity as many of your immediately available follicles as possible, while preventing them from ovulating prematurely.
It's important to understand that no amount of FSH will stimulate more follicles than are available to be recruited. The dose needs to be enough to stop the usual competition that takes place among them, but once that threshold is reached there isn't a lot of control possible over the number of recruits that will grow.
Secondly, using FSH injections does not use up follicles and their eggs any faster than they're already being used anyway. They actually began their development months earlier. And the non-recruits - those that don't produce mature eggs - are simply reabsorbed.
More is not better when it comes to FSH dosing. If the dose is too high it can be damaging to the eggs and may also put a woman at risk of ovarian hyperstimulation syndrome.
The duration of FSH administration is also important. The normal length of the follicular phase generally needs to be made available to the growing follicles, which takes 11 days or more. We usually check a woman's estrogen level after 3 or 4 days of stimulation. If there does not seem to be much response, the dose of FSH can be increased. If the response has been too brisk, the dose of FSH can be reduced gradually.
Patients have their first ultrasound after 7 or 8 days of stimulation. Ultrasonographers who are very familiar with follicle tracking perform the ultrasound examinations. The need for further monitoring will be determined by a woman's individual response, and may require blood tests and ultrasounds every other day until the follicles reach 18-20mm in diameter, large enough to contain a mature egg.
A 'natural cycle'
It is possible to have an IVF cycle without having any hormone treatment. This is called a 'natural cycle', and just one egg is collected for fertilisation in the laboratory. However, we want to make use of all the eggs that are developing in the month of treatment in order to give you the best chance at pregnancy with just one IVF cycle.
It's not possible to determine precisely how many eggs a woman has left. However, a doctor can get a sense of her 'ovarian reserve' by checking an FSH level and a pelvic ultrasound early in the cycle.
Preventing premature ovulation
Shutting down communication between the brain and the ovaries so that the eggs are not released before they can be collected
This is done using GnRH-analogs, a group of drugs closely related to the natural hormone gonadotrophin releasing hormone (GnRH), a hormone produced by hypothalamus in the brain that controls the release of FSH and LH by the pituitary gland. There are two types of analogs - agonists and antagonists - that prevent an LH surge in different ways.
GnRH agonists first cause a flare of FSH and LH as they stimulate and then inhibit, or down regulate, the pituitary. There are two kinds of agonists available in Thailand - a nasal spray and an injection forms. Your doctor will consider which form is suitable for your case.
GnRH antagonists are a newer class of injectable medication with the advantage that they drop levels of FSH and LH without first causing the flare, meaning they are given for a much shorter period of time. They are usually started on the sixth day of FSH stimulation. The antagonists, marketed in Thailand as Cetrotide® and Orgalutran®, are a little more expensive than the agonists and are no more effective in preventing the LH surge or in leading to pregnancy. Nonetheless, they may be of value in women who produce only a low number of eggs in an IVF cycle (particularly older women) or for women who prefer the convenience of a shorter treatment time. Which drug your doctor prefers to use will depend on factors such as age, previous response to treatment and convenience.
Replacing the LH surge at mid cycle with an injection of hCG
It's not presently possible to use synthetic LH to mimic the natural surge, as the duration of action of currently available LH is too short. Using hCG (human chorionic gonadotrophin) to replace the natural LH surge sets in motion everything that makes ovulation happen, causing the egg in the mature follicle to be fertilisable and loosening it from the wall of the follicle so that it comes out with the follicular fluid at egg retrieval.
It takes just over 38 hours for ovulation to occur after an injection of hCG. Eggs are mature and can float free from about 34 hours after hCG, giving a four-hour 'window' for egg retrieval, which is typically scheduled 36 hours after the hCG trigger.
hCG is marketed either as Pregnyl®, a powder or Ovidrel®, delivered in a pre-filled syringe. Your doctor will prescribe the suitable form for your case.
Intercourse must be avoided from Day 3 of FSH stimulation, as not all of the eggs might be collected. There is then a small chance of spontaneous conception, which increases the risk of a multiple pregnancy when additional embryos are transferred.