Introduction
The development of oocyte vitrification, with success rates now similar to fresh cycles,1 has enabled the opportunity to electively cryopreserve oocytes prior to the physiological decline in oocyte quality and quantity. Referred to herein as social egg freezing (SEF), it negates the age-associated deterioration in reproductive potential, but remains a controversial option owing to the multitude of ethical, legal, economic and obstetric related issues that it provokes.2 Whilst some have little alternative option, such as single women approaching their late-thirties who desire biologically related children,3 other indications include delaying childbearing for furthering education or to focus on career.4
Despite the theoretical benefit of preserving reproductive potential through SEF, it does not guarantee against involuntary childlessness.5 Following SEF, if women return to use their cryopreserved oocytes; risk of loss during thawing or following unsuccessful embryo transfer may result in potential exhaustion of cryopreserved oocytes prior to achieving livebirth. Replenishment may subsequently be difficult in the same woman at a later age owing to the inevitable physiological depletion in ovarian reserve.6 Therefore, at the time of SEF, it is important to maximise the number of oocytes retrieved for cryopreservation to improve the probability of a successful livebirth.7
Various characteristics are associated with oocyte yield such as age at time of oocyte retrieval.8 This encapsulates the very principle of SEF, and directly relates to the progressive depletion in primordial follicles and reduced neuroendocrine response to ovarian stimulation. This clinically manifests with poorer oocyte quantity and quality, as demonstrated by multivariate analysis to control for other confounding variables.9 Contrarily, increased BMI is associated with reduction in yield.10
The most accurate markers of ovarian reserve considered for prediction of oocyte yield following controlled ovarian stimulation are antral follicle count (AFC) and anti-Mullerian hormone (AMH).11 Endocrine markers including Oestradiol (E2), a measure of granulosa cell function has also been used.12 Elevated levels of follicle stimulating hormone (FSH) on day 2-3 of a cycle is associated with a significant reduction in yield, when compared to women with lower FSH of the same age.13 Radiologically, a follicular volume between 13-23mm/1-6mL at the time of ovulation trigger is also associated with optimal oocyte yields.14
The aim of this study was to assess the relationship between oocyte yield with clinical, biochemical and radiological markers including age, BMI, AMH, AFC, E2 and total number of follicles ≥12mm at trigger. A secondary aim was to report the reproductive outcomes following SEF in one of the largest reported cohorts in the UK so far.