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.