O-008 Low grade blastocysts result in healthy live births and should not be discarded

Study question

Does transfer of low grade blastocysts results in acceptable live birth rates the birth of healthy babies?

Summary answer

While BC/CB/CC blastocysts have a reduced chance of live birth compared with AA/AB/BA/BB blastocysts, the absolute chances are still reasonable.

What is known already

Transfer of poorer quality embryos and blastocysts result in lower live birth rates, though to what extent is unclear, nor if there is an absolute threshold below which live births are very rare or even do not occur. Further, the developmental competence of the inner cell mass (ICM) or trophectoderm (TE) could at least theoretically impact the pregnancy and/or the health of the baby. Many clinics do not transfer or freeze poor quality embryos and blastocysts, and prefer to submit the patient to a further stimulation cycle.

Study design, size, duration

We performed a retrospective analysis of 10,978 couples undergoing singleton blastocyst transfers between 2009 and March 2020. We included all single blastocyst transfers for which there was complete data on blastocyst quality, singleton or twin births, birthweight and gestation at delivery, irrespective of blastocyst grading, female age, cause of infertility, ovarian response or endometrial thickness. We recorded live birth rates, birth weight and gestational age.

Participants/materials, setting, methods

Data from 14 clinics in 3 countries, 8 from China, 5 from New Zealand, and 1 from Australia were included in the final dataset. We compared the impact of blastocyst grading using multiple logistic regression. Blastocyst grading was based on the Gardner classification, in which the first letter denotes the grade of the inner cell mass (A is best), and the second letter the grade of the trophectoderm.

Main results and the role of chance

Overall, 10,978 single blastocyst cycles resulted in 4,261 live births (38.8%) (4195 singletons and 132 twins). Live birth rates were 47% after transfer of AA blastocysts (n = 2306); 42% after AB/BA (n = 2088); 33% after BC (n = 1973); 25% after CB (n = 715) and 14% after CC (n = 117). There were too few AC (n = 27) or CA (n = 12) blastocysts to include in the analysis. The odds of live birth for BC/CB/CC blastocysts compared with AA/AB/BA blastocysts, vary between 0.8 and 0.9.

The live birth rate appears to be more dependent on ICM quality (C grade, n = 844, 23.2%) rather than TE quality (C grade, n = 2117, 32.1%), with the odds of live birth 0.43 and 0.57 respectively compared to A grade ICM or TE.

The average birth weight (singleton only) was 3336.9+/-570.3 g (range 3323 to 3386 g), and the average gestation at delivery (singleton only) was 38+6+/-2.0 weeks (range 38+2 to 39+1). There was no significant difference for birth weight or gestational age at delivery between blastocysts of different grades.

Limitations, reasons for caution

This was a retrospective study. Grading was based on inner cell mass and trophectoderm and not on degree of expansion, or on day of transfer.

It is likely that higher quality blastocysts were transferred first, in a fresh cycle, and poorer quality blastocysts frozen for later transfer.

Wider implications of the findings

The most important finding is that reasonable live birth rates are obtained in CC-blastocysts.

We therefore advocate that CC-blastocysts should be replaced or frozen for later transfer. It is reassuring that there was no impact of blastocyst quality on birth weights or gestational age at the time of delivery.

Trial registration number

Not applicable