P–694 Natural cycle vs Accumulation of oocytes. Which strategy is better for women with the poor ovarian response (POR)?
Authors: Bekzatova K , Shishimorova M 
Published: August 2021

Abstract

Study question
The aim of this study is to determine whether repetitive natural cycles (Strategy A) or oocyte accumulation (Strategy B) is a more effective strategy.

Summary answer
There was no statistical difference between the strategies however, the number of attempts for successful outcome with strategy A was lower than in strategy B.

What is known already
For populations with poor ovarian response natural cycles (NC) or modified natural cycles (mNC) with minimal stimulation have been implemented as a preferable option as opposed to conventional ovarian stimulation. Due to the development of advanced vitrification techniques, the accumulation of oocytes has become available.
Previous studies (2011, 2013, 2019) suggest that accumulation of oocytes could be a successful alternative to repetitive natural cycles for poor responders aged ≥35 years, showing higher clinical pregnancy rates. Moreover, the embryo-transfer cancellation and miscarriage rate were significantly lower in the oocyte accumulation strategy.

Study design, size, duration
Present retrospective cohort study included a selection of patients with POR treated from 2019–2020, which were divided into 2 strategies. Strategy A included 324 natural cycles or modified natural cycles with successful oocyte retrievals (Female mean age: 36.3 years). The strategy B consisted of 46 cycles with thawed oocytes that were accumulated through cryopreservation in several attempts (average n = 2,3) prior in NC or mNC (Female mean age: 37.6 years).

Participants/materials, setting, methods
POR was defined by following criteria: 1) advanced maternal age (≥35 years) or;
2) previous POR (≤3 oocytes with a conventional ovarian stimulation protocol);
3) abnormal ovarian reserve test;
The vitrification of the oocytes was performed using Kuwayama method (Cryotech®, Japan), while thawing was performed using Cryotop method (Kitazato®, Japan). Prior to fertilization, oocytes were cultured for 2 hours in IVF medium (Origio®, Denmark). The unsuccessful transvaginal oocyte retrievals (TVOR) were excluded from both strategies.

Main results and the role of chance
The clinical pregnancy rate per started cycle and per transfer in Strategy A vs Strategy B were 15,4% vs 15,2% and 28.08% vs 20%, respectively. Strategy A seemed to achieve higher rates; however, the difference was not statistically significant (Student’s t-test, p &lt; 0.05). Throughout all TVORs the rate of successful retrieval was 71.7%. The embryo-transfer cancellation rates in Strategy A vs Strategy B were 38,2% vs 8,69%, respectively. With strategy A the average amount of attempts for successful clinical pregnancy was 1.86. With strategy B the average amount of cryopreservations for oocyte accumulation was 2.3.

Limitations, reasons for caution
The number of patients in strategy B was significantly lower than in strategy A. Larger study with an increased number of samples is necessary to confirm the results. In addition calculation of cost-effectiveness in each strategy. The unsuccessful TVORs were excluded from both strategies, which significantly affects the statistical rates.
Wider implications of the findings: This study might help in developing and selecting more appropriate strategies for women with POR. The findings might help to determine the amount of time and attempts required for a successful outcome for patients aged ≥35. It can also be helpful in regulating the financial part of artificial reproductive technology.

Trial registration number
N/A