The value of FERs has already been reported in the embryo cryo-preservation chapter of this web page. Briefly, patients whom IVF treatment resulted in surplus embryos of good quality they may opt to freeze this for their subsequent utilization regardless the outcome of the initial treatment.
FER can be programmed either during a natural cycle (for normally menstruating recipients) or using a medicated protocol for endometrial preparation.
1. Natural Cycle FER
Individual patients are asked to receive a baseline ultra sound scan a few days prior to the middle of their cycle (i.e. before ovulation) so that their endometrium and ovaries are assessed. The ultra sound scan determines the size of the follicle destined to ovulate so that the time of ovulation is predicted. Moreover the quality and size of the endometrial lining is determined. The size of the endometrium should be consistent with the day of the menstrual cycle and therefore with the size of the follicle. As it has previously been described in this web page specialised cells within the follicle namely granulosa secrete estrogen which targets the endometrium which develops in size.
The rise in blood serum estrogen will signal the release of the LH hormone from the pituitary gland therefore ovulation is triggered. The determination of the exact timing of ovulation is of the essence during the natural cycle FER treatment. Otherwise the synchronization for optimal receptivity between embryo and endometrium will be compromised. Progesterone which is the hormone supporting embryo implantation into the uterus and its ongoing development is secreted with ovulation therefore a day 5 embryo must be replaced into the uterus exactly 5 days post ovulation confirmation. Triggering ovulation using an hCG injection other than allowing this to occur naturally allows for better control.
With the natural cycle approach the ovary will continue to support a potential pregnancy similarly to a natural conception. While it does not necessitate medication the natural cycle FER entails strict synchronization hence repeated ultra sound scans and estradiol blood tests are necessary. Certain clinics may advise progesterone supplementation starting with ovulation confirmation for additional endometrial support.
2. Medicated FER
The preparation of the uterus can be commenced as from the second day of a natural menstrual cycle or induced withdrawal bleed and the exogenous estrogen is normally administered at incremental dosages emulating the natural process. Along with estrogen pills the patient may be advised to administer transdermal skin estrogen patches. Aspirin for better blood circulation is also advised. Monitoring ultra sound scans and estradiol blood tests can be initiated as early as from day 6 from the onset of preparation and pending the findings of these examinations the initial estrogen dosage may be adjusted. At least two ultra sound scans will be required during a course of approximately 12-14 days on estrogen supplements. While the endometrium should develop to a satisfactory size during this period (minimum 7.0 mm and optimally 10 mm with a trilaminar appearance) certain individuals may require longer time to respond.
Progesterone is only prescribed once the endometrium has reached a satisfactory size. This hormone induces changes in the appearance of the endometrium (luteinized) which enters the second stage of the cycle namely the luteal phase. As previously described a 5 day embryo should be replaced exactly 5 days post progesterone commencement so optimal synchronization for embryo implantation is effected. While this protocol for endometrial preparation incurs literally no inconvenience to the patient and is not associated with any side effects the administration of estrogens early in the menstrual cycle does not necessarily hinder the ovary from responding towards maturing a follicle itself. Indeed this possibility (approximately 15-20%) must be examined while monitoring scans are being undertaken. In the event that a follicle is developing there are two ways forward which can be contemplated therefore prevent the cancelation of the treatment cycle.
The first approach is to schedule progesterone commencement on the day of ovulation and therefore proceed with embryo thawing in a synchronized fashion provided that the endometrium had built up sufficiently or administer daily injections of an antagonist to hinder ovulation. If so the antagonist as previously documented in the ovarian stimulation protocols chapter of this web page must be commenced when the follicle has reached a mean size of 14-15 mm. Ovulation can then be confirmed following an hCG injection similarly to stimulated cycles. While it may be inconvenient and more expensive to the patient the safest method to prevent follicular development is to suppress ovarian function by down regulating the hypophysis similarly to the first phase of a long protocol regime (see ovarian stimulation protocols). This entails the administration of an agonist (in depot form or using daily dosage) one week following confirmation of ovulation during the previous cycle. A drawback of the medicated FER is that the patient is subjected to the continuous use of both estrogen and progesterone until the 12th week of gestation. At that stage the placenta takes over the nutrition of the pregnancy.