C. Albert

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.

A time to look back: analysis of morphokinetic characteristics of human embryo development

OBJECTIVEnTo describe the times associated with the morphological changes that occur in the embryo during preimplantation development based on the largest sample size described with time lapse.nnnDESIGNnCohort study.nnnSETTINGnUniversity-affiliated private center.nnnPATIENT(S)nA total of 9,530 embryos from 1,806 intracytoplasmic sperm injection (ICSI) cycles.nnnINTERVENTION(S)nNone.nnnMAIN OUTCOME MEASURE(S)nUsing a time-lapse system, embryo images were acquired for at least 68 hours, in some cases reaching 120-130 hours. Embryo cleavage time points up to 8-cell-stage (t2-t8) as well as morulae (tM) and blastocyst formation (tB) were registered in hours after ICSI. Additionally, duration of the cell cycle (cc) and synchrony (s) of the second and third cell cycles were defined. Finally, four subgroups of embryos were considered: the regular divisions group excluded embryos with a direct cleavage from 1 to 3 or 2 to 5 cells, and the viable 8-cell, the viable blastocyst, and implanted embryos groups included only embryos viable to the 8-cell stage, blastocyst stage, or transferred and successfully implanted, respectively.nnnRESULT(S)nAverages of times in the general population were: t2 = 27.9 hours, t3 = 38.2 hours, t4 = 40.7 hours, t5 = 51.0 hours, t6 = 54.1 hours, t7 = 56.7 hours, t8 = 59.1 hours, tM = 86.6 hours, tB = 104.1 hours, cc2 = 10.3 hours, cc3 = 12.8 hours, s2 = 2.7 hours, and s3 = 9.9 hours. Comparison between groups showed significant differences between regular divisions and viable 8 cells for t2, t3, t5, cc2, cc3, s2, and s3; between 8 cells and blastocyst for t5, t8, tM, cc3, and s2; and between blastocyst and implanted embryos for t8, tM, tB, and s2. Differences in timing related to morphology of cleavage- and blastocyst-stage embryos were detected.nnnCONCLUSION(S)nA time-lapse monitoring system applied to embryology allows accuracy and objectivity when defining the basis of embryo development within a clinic. The sample size is the largest ever described that provides consistent information about the normal distribution of embryo developmental timings.