O-279 The type of gonadotrophin: Does it improve ART outcome?
Authors: Sunkara S.K 
Published: June 2022

Abstract
Ovarian stimulation is a vital clinical component of an IVF cycle, with gonadotrophins being the main stimulation drugs. Follicle stimulating hormone (FSH), the key driver of follicle recruitment during an ovarian cycle is a complex glycosylated protein comprised of an α and β subunit with four glycosylation sites. Differences in glycosylation lead to heterogeneity with the FSH isoforms varying in their receptor binding and biological activity. The cyclic physiological variation of FSH isoforms and the FSH threshold/ window concept lead to the selection of a single dominant follicle during a menstrual cycle. Surpassing the FSH threshold and extension of the FSH window with ovarian stimulation using gonadotrophins salvages follicles with higher FSH sensitivity leading to multi-follicular development and retrieval of multiple oocytes.
The first IVF birth in 1978 was from a natural cycle and was preceded by several unsuccessful attempts at oocyte retrieval. Ovarian stimulation was therefore incorporated into IVF treatment to overcome the inefficiencies encountered with a natural cycle. The objective of ovarian stimulation during IVF treatment is to obtain several mature oocytes, leading to good quality embryos for immediate replacement and cryopreservation for future use. An ideal stimulation wherein gonadotrophins are the mainstay is one that achieves maximal efficacy, safety and cost-effectiveness.
Several gonadotrophin preparations have been available for clinical use over the years since the first use of pregnant mare serum gonadotrophin (PMSG) in 1940 and the first successful birth using human pituitary gonadotrophin (hPG) in 1961. These initial preparations were soon abandoned due to concerns with antigenicity and safety. Subsequent important milestones in the development gonadotrophins for clinical use include the urinary derived products, recombinant FSH preparations, long acting FSH and the biosimilars. Given the selection of gonadotrophins currently available, the apparent question is if they differ?
Circulating FSH isoforms change during different stages of the menstrual cycle and through the reproductive stages. More acidic isoforms are predominant during the early follicular phase, with less acidic or basic isoforms predominant in the late follicular phase of the menstrual cycle, and more acidic isoforms during the menopausal stage. Similarly, the different FSH products vary in their properties owing to differences in their production and purification. Urinary derived products are more acidic compared to recombinant preparations and the different recombinant products vary in degree of acidity due to differences in the extent and pattern of glycosylation. The acidic and basic properties of gonadotrophin types influence metabolic stability, half-life and their biological activity. The question then remains if these differences in bioactivity affect clinical outcomes?
Clinical effectiveness of the various gonadotrophins types should be addressed in the context of the different pituitary suppression regimens, ovarian response categories and patient variables given the implementation of individualised stimulation protocols. It is also imperative to clearly define successful clinical outcomes incorporating both efficacy and safety. Cumulative live birth rate (CLBR) following fresh and frozen embryo transfers resulting from one episode of ovarian stimulation should be adopted as the measure of the overall efficiency along with OHSS as a measure of immediate safety. There are several studies and systematic reviews comparing the different gonadotrophin types and products for various outcomes including surrogate endpoints, with inconsistent results attributed to differences in the inclusion/ exclusion criteria, heterogeneity across studies and varied quality of the primary studies. Furthermore, there have been sparse studies reporting on CLBR and there is a continuing debate on what would be considered as a relevant clinical difference in efficacy.
In addition to efficacy and safety, the ultimate choice of gonadotrophin should be based on regional availability, patient acceptability and cost-effectiveness for a live birth.