Ratio between inner cell mass diameter and blastocyst diameter is correlated with successful pregnancy outcomes of single blastocyst transfers

A high ratio of inner cell mass diameter to blastocyst diameter is correlated with successful implantation and can be used as a predictor of pregnancy in single blastocyst transfers.

Volume 106, Issue 6, Pages 1386-1391


Miriam Almagor, Ph.D., Yael Harir, Ph.D., Sheila Fieldust, B.A., Yuval Or, M.D., Zeev Shoham, M.D.



To evaluate the ability to predict pregnancy outcomes of single-blastocyst transfers by measuring the ratio of inner cell mass (ICM) diameter to blastocyst diameter using time-lapse images.


Retrospective cohort study.


University-affiliated medical center.


One hundred twenty-seven women undergoing a total of 129 blastocyst transfers with intracytoplasmic sperm injection.


Embryo monitoring by time-lapse microscopy.

Main Outcome Measure(s)

The ratio of ICM diameter to blastocyst diameter in single-blastocyst transfers and clinical pregnancy rates.


In phase I of the study, 63 women underwent 65 single blastocyst transfers that resulted in 25 pregnancies (40% of the women). The successfully implanted blastocysts had an average ICM/blastocyst diameter ratio of 0.487 ┬▒ 0.086, whereas the average ICM/blastocyst ratio of nonimplanted blastocysts was significantly lower (0.337 ┬▒ 0.086). The live-birth rate was 29% (18/63). In phase II, 64 single-blastocyst transfers were performed in 64 women. The ICM/blastocyst diameter ratio was measured, and blastocysts with the highest ratios were chosen for transfer. Forty-three women (67%) with an average ICM/blastocyst diameter ratio of 0.46 achieved pregnancy, and 36 of the 43 pregnancies (84%) resulted in the delivery of a healthy baby. In the 21 women (33%) who failed to achieve pregnancy, the average ICM/blastocyst ratio was 0.45. The resultant positive predictive value was 74%, and the negative predictive value was 70%.


The ICM-to-blastocyst diameter ratio is a predictor of implantation and live birth in single-blastocyst transfers, offering a simple, noninterfering method to select blastocysts with high developmental capacity.

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Go to the profile of Micah J Hill
over 5 years ago
Thank you for your interesting article. I have a comment and a question for you. First, you note that your study did not find association of the trophectoderm grade and live birth, whereas our study did (Hill et al, F&S, 2013). You hypothesize this is because the time lapse gives a more uniform measurement of when the embryo is evaluated. I would propose it may also be a sample size issue, given that our study had almost 700 patients and your study 60 patients in phase I and II. Our data is also consistent with that from Ahlstrom et al, Thompson et al, and Honnma et al. Taken together, those studies represent over 5,000 embryo transfers studies demonstrating the strong association of the trophectoderm with pregnancy. So the lack of association in your study is most likely explained by lack of statistical power and type II error. Second, does adding the ICM/blastocyst diameter ratio result in improved incremental probability in predicting birth over what we already look at in embryo morphology? In other words, we already look at the ICM grade in addition to the trophectoderm and expansion. Does this new ratio improve predictive ability above those other components? This is especially important when a new ratio is made from parameters that we already look at. One way to do this would be to create sequential multivariate ROC curve analysis, adding in each variable one at a time. Is the AUC for ICM/blast + ICM + TE grade + expansion any better than the AUC for just ICM + TE grade + expansion? This would be helpful to know if the ratio adds incremental predictive probability to the model.