Arancha Galán

Implantation rates after two, three, or five days of embryo culture.

Extended embryo culture together with amelioration of embryo selection methods and embryo culture conditions have allowed a substantial increase on both pregnancy and implantation rates. However, uterine embryo transfers are still performed after 2 to 6 days of egg retrieval. In this paper, we show the results of two studies, one prospective study comparing IVF outcome of day 2 and day 3 embryo transfers, and a retrospective study looking at blastocyst transfers versus day 3 embryo transfers in our egg donation program. Also, we test the predictive value of the presence of three or more seven cell-stage embryos on day 3 of development on blastocyst formation and pregnancy rates. No significant differences were found between day 2 and day 3 embryo transfers in terms of pregnancy, ongoing pregnancy, and implantation rates, as well as in multiple and in high order pregnancy. In general, day 6 embryo transfers resulted in significantly higher ongoing pregnancy and implantation rates compared with day 3 embryo transfers (41.1 per cent and 23.6 per cent versus 50.1 per cent and 38.1 per cent, respectively). No differences were found in terms of multiple gestations despite transferring significantly more embryos on day 3 compared with day 6 transfers. When less than three 7-cell embryos were present in the embryo cohort, day 6 embryo transfers did not improve the rates of ongoing pregnancy with regards to day 3 embryo transfer, although significant high implantation rates were obtained on the group of blastocyst transfer. The presence of three or more 7 cell-stage embryos improved significantly both ongoing pregnancy and rates on blastocyst transfers compared to day 3 embryo transfers (65.6 per cent versus 50.6 per cent and 37.4 per cent vs 24.7 per cent, respectively). In conclusion, at least in egg donation, day 3 embryo transfers do not improve either pregnancy or implantation rates when compared to day 2 transfers. Generally speaking blastocyst transfers give significantly higher chance of pregnancy and implantation rates per cycle and per transfer than early cleavage stage transfers. However, the absence of a good embryo cohort, that is having less than three 7 cell-stage embryos on day 3, blastocyst transfers will improve implantation rates but not ongoing pregnancy rates.

Reduced oxygen tension improves embryo quality but not clinical pregnancy rates: a randomized clinical study into ovum donation cycles.

OBJECTIVE To investigate the effect of low O2 tension during in vitro culture in terms of ongoing pregnancy rates in ovum donation cycles. DESIGN Randomized trial. SETTING Private university-affiliated IVF center, university-based hospital. PATIENT(S) A total of 1,125 cycles of ovum donation. INTERVENTION(S) Embryo culture in an atmosphere of 5.5% CO2, 6% O2, and 88.5% N2 versus a dual-gas system of 5.5% CO2 in air. MAIN OUTCOME MEASURE(S) Ongoing clinical pregnancy rates per intention-to-treat (ITT) patients. RESULT(S) The use of low O2 tension achieved a 41.3% ongoing pregnancy rate per ITT compared with a 40.8% rate obtained for 5% CO2 in air. The mean number of blastomeres and the percentage of top-quality embryos were significantly higher after lower O2 concentration during in vitro culture (7.1 ± 3.6 and 28.6% vs. 7.3 ± 8.4 and 32.1%, respectively). CONCLUSION(S) In the ovum donation cycles undergoing day-3 embryo transfers, the use of low O2 tension did not improve ongoing pregnancy rates per cycle and per transfer. However, it benefited embryo quality, demonstrating the potential negative impact of high O2 tension on the in vitro embryo development.

Analysis of the morphological dynamics of blastocysts after vitrification/warming: defining new predictive variables of implantation

OBJECTIVE To describe the morphological dynamics of vitrified/warmed blastocysts and to identify quantitative morphological variables related to implantation. Subsequently, by using the most predictive parameters, to develop a hierarchical model by subdividing vitrified/warmed blastocysts into categories with different implantation potentials. DESIGN Observational, retrospective, cohort study. SETTING University-affiliated private IVF center. PATIENT(S) The study included 429 vitrified/warmed blastocysts with known implantation data, which were evaluated by time-lapse imaging. Blastocysts were routinely placed in EmbryoScope (Vitrolife) immediately after warming until transfer. INTERVENTION(S) None. MAIN OUTCOME MEASURE(S) Embryos were vitrified and warmed by the Cryotop method (KitazatoBiopharma). The studied variables included the initial and minimum thicknesses of zona pellucida (μm), the initial and maximum areas (μm2), the area of inner cell mass (μm2), expansion (whether the embryo reexpands or not after warming), and collapsing or contraction after warming. After defining the optimal ranges according to the consecutive quartiles with the highest probability of implantation, a logistic regression analysis was performed by combining the former variables and the blastocyst morphological classification criteria defined by the Spanish Association of Embryologists into A, B, C, or D categories. RESULT(S) Reexpansion of vitrified/warmed blastocysts correlated strongly with implantation (44.6% for reexpanded vs. 6.5% for the blastocysts that did not reexpand after warming). Throughout the logistic regression analysis, the model identified the maximum blastocyst area, odds ratio (OR) = 0.41 (95% confidence interval [CI], 0.22-0.77), followed by the initial area, OR = 0.62 (95% CI, 0.35-1.08) as the most predictive variables related to implanting embryos. Blastocyst morphology was not considered relevant in our model. The hierarchical tree model subdivided embryos into four categories, A-D, with lowering expected implantation potentials (from 47.3% for A to 14.2% for D). CONCLUSION(S) The analysis of warmed blastocysts by time-lapse imaging may provide objective quantitative markers for the blastocyst implantation potential. We propose a hierarchical model to classify vitrified/warmed blastocysts according to their implantation probability. The observed correlations and the proposed algorithm should be validated in a prospective trial to evaluate its efficacy.

Embryo-Maternal Dialogue in the Apposition and Adhesion Phases of Human Implantation

Embryonic implantation, which is the process by which the human embryo orientates, attaches, and finally invades the underlying maternal endometrial tissue is a highly regulated mechanism. Embryonic implantation requires a receptive endometrium, a competent blastocyst, and a coordinated development and communication between them. Considerable advances have been made in understanding the cell biology of the embryo and the maternal endometrium separately. Nevertheless, communication between them, and the reciprocal effect on each other, constitute an exciting and as yet unsolved paradigm in reproductive medicine. This embryo—maternal dialogue is differentially regulated in an autocrine/paracrine manner during the apposition and adhesion phases. We will show in this chapter the capacity of the human embryo to regulate the endometrial antiadhesion molecule MUC1 to prevent unwanted attachment in the apposition phase and to allow selective attachment in the adhesion phase. In addition, similar coordinated mechanism will be shown for the embryonic regulation of endometrial epithelial cell (EEC) apoptosis in the apposition and adhesion phase of human implantation.