Suzanne HodgsonResearcher in Statistics & EpidemiologySCAAC 12 June 2013Updated Blastocyst Analysis
IntroductionTwo years ago we looked at benefits and risks of blastocyst transfers, compared with cleavage stage transfers
Areas of concern were success rates, monozygotic twinning, gestation & birth weight, abnormalities and the sex ratio.
At the time data was up to 2008, now 2010 for births 2011 for pregnancies
Last time we saw..There was some evidence that: pregnancy and birth rates are higher for BTs than CTs DBT has very high MB rates, blastocysts may result in more MZ twins; the sex ratio is skewed in favour of males, particularly after eSET There did not seem to be evidence that: there is a difference in birth weightthere is a difference in gestation
Change over timeThen: BTs were a relatively new procedure in the UK, but growing.
7% in 2006, 12% in 2008 and in 2010 blastocysts formed nearly a quarter of all embryo transfers
2012/3 over 40%, and still with a steady upward trend.
Changes in embryo stage at transfer
2008 to June 2012
Pregnancies and birthMust take great care comparing CT and BT success rates they are likely to be different types of patient.
Cleavage: pregnancy rate per transfer 28.2% (2011)live birth per transfer 25.8% (2010)
Blastocyst:pregnancy rate per transfer 46.3% (2011)live birth per transfer 41.4% (2010)
Age specific live birth rates per ET2010
Age specific pregnancy rates per ET2011
Multiple birthsOverall in 2010, 20.1% of live births after CTs were of two or three babies, and 19.9% after BTs.
High multiple birth rate after double BTs 34.8% compared with 24.6% after DCTs.
In women under 35 this is even more pronounced, 40.0% of births are multiples after DBT
Monozygotic twinsFew outcomes annually so data has been aggregated over 2 yearsThere is much variation year to yearCan only count where babies born is greater than embryos transferred
CleavageBlastocyst2 babies from SET24/2,45149/2,9653 babies from DET24/12,94645/4,394Total (%)48/15,398 (0.3%)94/7,362 (1.3%)
GestationNo significant difference between CT and BT for singletons or twins
Birth weight - singletonsInitially singletons only
Cleavage mean birthweight:3,247g (CI:3,231 3,264g)
Blastocyst mean birthweight:3,237g (CI: 3,256 3,259g)
As before, not statistically significantly different
Birth weight - multiplesMultiples may have very different birth weights but same gestation
Looked at whether one or more babies were of low birth weight (
Congenital abnormitiesAbnormalities are recorded in live births, still births, terminations & miscarriages.
For babies born alive, 2010 saw 773 congenital abnormalities, 27 uncertain
RR for 2010: 0.49 (95% CI: 0.41 0.57)
RR for aggregated 2009 & 10: 0.39 (95% CI: 0.34 0.44)
Apparent reduction in risk after BT.
Sex ratio (2008)
MaleFemaleAll births (ONS)5149BT overall5446CT overall5050BT singletons5545CT singletons5149eSBT5743eSCT4654
Sex ratio (2010)
MaleFemaleAll births (ONS)5149BT overall5248CT overall5050BT singletons5347CT singletons5050eSBT5248eSCT5149
ConclusionsThe proportion of embryos transferred at blastocyst stage continues to increase, now nearly half.
We now have more evidence that: success rates are higher for BTs than CTs blastocysts may result in more MZ twins; DBT has very high MB rates
There does not seem to be evidence that:there is a difference in birthweight or gestation
There is less evidence of:skewing of the sex ratio
But not really that much data, we looked at 2008 data when BTs were still very much in the minority. Now, BT has continued to grow so we decided to look again at this.
*This down from 2008, as we knowIs the blasto rate lower because eSET is more likely to be Blasto? SH check
*For two babies from SET the sex is checked to ensure identical twins, in one case in 2010, 2 in 2009 the sexes were different so this was removed an error must have occurred somewhere.Relative Risk = 0.5, CI 0.4-0.6 P