Suzanne Hodgson Researcher in Statistics & Epidemiology SCAAC – 12 June 2013 Updated Blastocyst Analysis

Introduction Two 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 weight there is a difference in gestation

Change over time Then: 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 birth Must 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 ET 2010

Age specific pregnancy rates per ET 2011

Multiple births Overall 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 twins Few outcomes annually so data has been aggregated over 2 years There is much variation year to year Can only count where babies born is greater than embryos transferred CleavageBlastocyst 2 babies from SET24/2,45149/2,965 3 babies from DET24/12,94645/4,394 Total (%)48/15,398 (0.3%)94/7,362 (1.3%)

Gestation No significant difference between CT and BT for singletons or twins

Birth weight - singletons Initially 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 - multiples Multiples may have very different birth weights but same gestation Looked at whether one or more babies were of low birth weight (<2,500g) Very similar proportions after CT, 69.8% and BT, 68.9% Similar to that seen last time, and around the same as the NPEU analysis 2006 (66%)

Congenital abnormities Abnormalities 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.

MaleFemale All births (ONS)5149 BT overall5446 CT overall50 BT singletons5545 CT singletons5149 eSBT5743 eSCT4654 Sex ratio (2008)

Sex ratio (2010) MaleFemale All births (ONS)5149 BT overall5248 CT overall50 BT singletons5347 CT singletons50 eSBT5248 eSCT5149

Conclusions The 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

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