Comparative Efficiency of IVF Between Frozen-thawed and Fresh Oocytes: A Meta-Analysis

Abstract

Despite the proliferation of numerous small reports of pregnancies after oocyte cryopreservation, the true efficiency of this procedure is unknown. Our ojectivewas to perform a meta-analysis to determine the efficiency of oocyte cryopreservation relative to IVF with fresh oocytes. Meta-analysis of ICSI cycles with frozen-thawed oocytes in comparison to a matched control group undergoing IVF-ICSI with fresh oocytes (FC) in a large ART program. All manuscripts and abstracts on oocyte cryopreservation with slow freeze (SF) and vitrification (VF) from 1986-2005 were identified from Medline, reference lists of authoritative reviews, and abstract books. Five reports on inseminated frozen-thawed oocytes were excluded as ICSI is the current standard for fertilization of these oocytes. From the patients who underwent IVF between 2002-2003 in our program and whose delivery information was available, 505 age-matched consecutive ICSI cycles with 4492 oocytes were used for comparison. Fifty-three % (2687/5101) and 69% (497/720) of oocytes survived thawing after SF and VF, correspondingly. Clinical and live birth rates per oocyte frozen with SF was 1.6% and 1.1%, and with VF these numbers were 1.7% and 1.6%. Clinical pregnancy and live birth rates per oocyte thawed after SF and VF were 2.3% (118/5200) and 1.7% (88/5200), and 1.9% (14/720) and 1.8% (13/720), respectively. The corresponding mean number of embryos transferred in FC, SF and VC were 2.5, 2.7, and 4. Comparisons of pregnancy and implantation rates between IVF with frozen-thawed versus fresh oocytes are shown in table 1. The odds ratios of live birth (delivery) per injected oocyte and embryo transfer were 0.49 and 0.30 compared to FC. The odds ratios for implantation were 0.29 and 0.13 with SF and VF methods in comparison to FC. One hundred and twenty-two children were born from crypreserved oocytes. Of the pregnancies, 81.2% were singleton, 16.8% were twins, and 1% were triplets. This compares to 59.6% singletons, 37.3% twins, and 3.1% triplets in patients undergoing IVF with fresh oocytes in our program. Tabled 1 Clinical and live birth pregnancy rates/ET with oocyte cryopreservation are lower compared to success rates with fresh oocytes in our program. But the magnitude of this difference becomes smaller when these rates are compared to SART 2002 data (clinical pregnancy and live birth/ET, 43% and 37.5%, respectively for age 32). Notwithstanding the limitations of this meta-analysis, SF is neither as inefficient as it is currently portrayed nor is it as effective as IVF with fresh oocytes. In contrast, VF cannot be recommended at this time because of low implantation rates and limited number of live births. It appears that the low implantation rates with VF are being compensated by the transfer of large number of embryos.