Effectiveness of different protocols for slow freezing of human blastocysts
Učinkovitost različnih postopkov počasnega zamrzovanja človeških blastocist

english

2011

volume 80, supl.

fertilization   human pregnancy

Slovensko zdravniško društvo
(Obvezni izvod spletne publikacije)

Background: Pregnancy rate after the transfer of frozen / thawed human blastocysts has been lower in comparison with the pregnancy rate in vitro fertilization (IVF) cycles with fresh embryos. There is a need for the optimization of freezing protocols. Methods: In the years between 2000 and 2004, blastocyst culture was performed on 3087 IVF/ ICSI cycles. In the cases with more developed blastocysts one or two were transferred into the uterus. In 1031 cycles the surplus blastocysts were cryopreserved using one of four slightly modified two-step freezing, two-step thawing glycerol protocols. In protocol A (n = 41) we used a complex freezing medium (modified Ham F-12) and in the others (B, C, D) a simple one (without amino acids). In protocol B (n = 177) the blastocysts were thawed according to four-step thawing protocol. Protocol C (n = 81) retained two thawing steps. Protocol D (n = 37) was the same as C, but with the addition of hyaluronan into the freezing medium. Eight hundred thirty-four frozen blastocysts were thawed for transfer in 336 thawing cycles. In the retrospective study we compared survival according to blastocyst quality (in Groups B-D) as well as pregnancy and delivery rates between different protocol groups. We also compared the clinical outcome between the transfers of thawed blastocysts in natural (n = 249) or artificial cycles (n = 80). Results: The blastocyst survival rate does not differ between protocols B, C and D (68.7 % vs. 64.8 % vs. 69.8 %), but it was lower in Group A (53.2 %, P < 0.05). In groups B, Cand D, the morphologically optimal blastocysts survived cryopreservation in82.3 % vs. 81.1 % and 88.9 %, the suboptimal blastocysts survived in 67 % vs. 64.6 % and 64 % and poor blastocysts in 49 % vs. 48.7 % and 66.7 %, respectively. The clinical pregnancy rate was lower in Group A in comparison with Groups B, C and D (9.8 % vs. 21.5 % vs. 18.5 % vs. 16.2 %; P< 0.1). The mean delivery rate per thawing was 15.2 %. When at least one optimal blastocyst was thawed and transferred into the uterus, the clinical pregnancyrate was significantly higher than in cycles with only suboptimal blastocysts (27.4 % vs. 14.7 %, P< 0.05). The implantation rate and take- home-baby rate per one thawed blastocyst were higher when blastocysts were replaced in natural than in artificial cycles (15.4 % vs. 8.2 % and 8.3 % vs. 3.8 %; P < 0.05). Conclusions: All freezing protocols using a simple freezing medium were more effective than protocol with a complex medium. Their application in IVF patients with frozen surplus blastocysts (these patients delivered in fresh cycles in 51.4 %) increases the cumulative delivery rate by an additional 15.2 % with every thawing cycle. The morphology of blastocysts and cycle preparation for transfer had the strongest influence on the success of freezing programme.

30.01.2012