Analysis of factors affecting embryo implantation

Transcription

1 Analysis of factors affecting embryo implantation Andrew L.Speirst, H.W.G.Baker and Nusratudin Abdullah The Royal Women's Hospital, Melbourne, Australia ITo whom correspondence should be addressed Introduction The data analysed here represents all cycles managed at our in-vitro fertilization (IVF) programme at The Royal Women's Hospital and Melbourne IVF Clinic, Australia, over the 5 years to December There were embryos replaced in 6831 cycles of 2214 patients. Preliminary data are given here; a full report will be published in due course. Ovarian stimulation was with clomiphene citrate plus human menopausal gonadotrophin (HMG) in 2503 cycles and a 'flare' protocol using luprolide (Lucrin; Abbott, Kurnell, Australia) plus HMG in 1338 cycles. Egg retrieval was timed h after the administration of 5000 IV human chorionic gonadotrophin (HCG). Cryopreservation of embryos was generally undertaken 2 days after egg retrieval using a 1,2-propanediol-sucrose slow freeze-rapid thaw method (Lassalle et a!., 1985). Embryo cryopreservation was increasingly employed over the years covered by this study, and by the end of the period accounted for half of the embryo transfer procedures. The diagnosis of clinical pregnancy was based on finding gestation sac(s) on ultrasound examination or an ectopic pregnancy (considered to be a single gestation sac). Each gestation sac is described as an 'implantation' in this study. Logistic regression analysis was used to identify factors most likely to be associated with successful implantation. It should be stressed that by this analysis, the chance of implantation for each embryo replaced can be analysed for an independent association with any of the factors studied, whilst simultaneously taking into consideration the effect of the other factors. Results Do embryos help each other? Table I shows the implantation rate per 100 embryos replaced, broken down by the number of embryos replaced together. The average implantation rate was Human Reproduction Volume II Supplement I 1996 European Society for Human Reproduction and Embryology 187

2 A.L.Speirs et al Table I. Do embryos transferred together help each other? No. embryos Total no. Total no. transferred transfers embryos Total implantations Total anot significant by logistic regression. Table II. The effect of a difficult embryo transfer Ease of transfer Normal Difficult Total no. transfers ap = by logistic regression. Total no. embryos (7.2) 659 (7.8) 225 (6.9) 53 (7.6) 1034 (7.5) 864 (7.8) 172 (6.4) 7.5%. If embryos help each other then embryos replaced in threes and particularly in fours should produce more implantations per 100 embryos than those replaced alone or in pairs (other things being equal). With multiple factor logistic regression analysis allowance is made for the simultaneous effect of other factors. There was no practical or statistical evidence that embryos helped (or hindered) each other. The effect of a difficult embryo transfer procedure A trans cervical catheter was passed with ease on 5525 occasions and with some difficulty on 1306 occasions. The more difficult transfers reduced the implantation rate from 7.8 to 6.4%, a one-fifth reduction (Table II). The effect of age The detrimental effect of increasing maternal age on implantation has been noted before, but was strongly demonstrated in this analysis. When compared with those aged <30 years, the year old group suffered a 23% reduction in implantation rate, and the group aged :;:,:40 years had half the success of the younger group (Table III). The effect of number of months of treatment The probability of implantation was similar for each of the first four embryo transfer procedures, but dropped by one sixth in the fifth cycle and by 30% for 188

3 Factors affecting embryo implantation Table III. The effect of maternal age Age Total no. Total no. (years) transfers embryos (9.0) (8.8) (8.0) (6.8) > (4.4) Table IV. Effect of number of treatments on implantation No. Total no. Total no. treatments transfers embryos (8.8) (7.8) (8.5) (7.8) (6.9) > (5.9) Table V. Effect of previous implantation Previous IVF Total no. Total no. implantations transfers embryos (7.3) (9.3) (10.3) (33) ap = by logistic regression. the 3716 embryos transferred in sixth or later cycles (Table IV). The logistic regression analysis showed this effect to be independent of the other effects such as age and difficulty of transfer. The effect of previous IVF implantations There was a clear association demonstrated between previous IVF implantation and an increased likelihood of implantation with subsequent transfer procedures (Table V). This information can be of some (slight) comfort to patients who have just suffered a failed IVF pregnancy and are considering further treatment. 189

4 A.L.Speirs et al. Table VI. The usefulness of oocyte quality scoring Average oocyte Total no. Total no. quality transfers embryos Good Fair Poor (8.1) 715 (7.5) 34 (5.2) ap = by logistic regression. Table VII. The usefulness of embryo quality scoring Average embryo Total no. Total no. quality transfers embryos Good Fair Poor The usefulness of oocyte scoring 189 (9.2) 750 (8.0) 97 (4.2) Oocytes were graded according to standard criteria as 'good', 'fair', or 'poor'. A difficulty of the analysis of these data is the need to average oocyte quality; the replacement of two embryos, one from a 'good' oocyte and one from a 'poor' oocyte is the same as two embryos from 'fair' oocytes. Nevertheless the oocyte score was found to be strongly correlated with an improved chance of implantation for the embryos formed after IVF (Table VI). The usefulness of embryo scoring Embryos were also graded according to standard criteria as 'good', 'fair', or 'poor'. The average embryo score was also strongly correlated with an improved chance of implantation after embryo transfer (Table VII). This finding provides justification for the practice of simultaneously transferring more embryos if they are of poorer quality, without too much concern at the possibility of a triplet pregnancy. The effect of embryo cell number at transfer Embryo transfer was carried out 2 days after egg retrieval during the period analysed. Most embryos (82%) were at the 3-6-cell stage. The chance of implantation was clearly less for 1- or 2-cell embryos (regardless of quality) or possibly for embryos found to have >6 cells (Table VIII). 190

5 Table VIII. The effect of embryo cell number at embryo transfer Factors affecting embryo implantation Cell no. at Total no. Total no. embryo transfer transfers embryos (4.6) (8.0) (8.8) > (5.8) Table IX. The effect of embryo cell loss during freeze-thaw Cells lost Total no. Total no. on thawing transfers embryos (9.4) (5.5) (6.2) > (1.5) The effect of cell loss on embryo thawing The loss of cells during the freezing-thawing process was identified as an important predictor of reduced success (Table IX). It should be stressed that this effect was in addition to the effect of cell number described in the preceding section. It was clear that there was an increased probability of success with embryos fully intact after thawing. Conclusion Logistic regression analysis is an excellent tool for analysing the factors affecting implantation in a large and complex data set such as this. The most important beneficial effects identified were: (i) improved average oocyte and embryo quality; (ii) more cells transferred (up to six); (iii) fewer cells lost on thawing; (iv) age of woman <35 years; (v) previous IVF implantations; (vi) ease of embryo transfer. There was no evidence that embryos helped (or hindered) each other when replaced together. References Lasalle, B., Testart, T. and Renard, J.P. (1985) Human embryo features that influence the success of cryopreservation with the use of 1,2-propanediol. Fertil. Steril., 44,