Day 5 versus day 6 blastocysts

My doctor’s office has suggested it sees similar success rates with frozen day 5 and day 6 embryos, so I never really worried about the fact that many of our embryos were day 6. 

(http://3yearwait.blogspot.com/2014/08/my-snow-babies.html)

I’m reconsidering.  I have used three day 5 embryos.  They have all “worked.”  (My son, blighted ovum at 6 weeks, and anencephaly pregnancy.)  Of course they were also B2s, so good quality.  And they were also all fresh.  So they were the best of the bunch—they should have been the best ones.  I’ve also used four day 6 embryos.  None of them have worked.  (Chemical pregnancy, no pregnancy, and my last two with HCG of 2 and 1.)  Of course 3 of the 4 were poor quality B3s.  And all were frozen.

I mean, it makes sense that the more advanced the embryo, the more likely it is to work.  Fully hatched > hatching > nothing.  No surprise that the fastest embryo out of the gate is the most likely to work.

This article suggests that similarly developed frozen day 5 versus day 6 embryos have similar success rates (like my clinic suggests):

http://humrep.oxfordjournals.org/content/early/2010/06/11/humrep.deq143.full

“[A]nalysis of those studies where the Day 5 and Day 6 blastocysts had the same morphological quality at the time of freezing showed no difference in clinical pregnancy and ongoing pregnancy/live birth rates.”

This article agrees:

http://link.springer.com/article/10.1111%2Fj.1447-0578.2008.00203.x

However, the fresh results are not the same:

http://www.ncbi.nlm.nih.gov/pubmed/11384637

“Embryos that develop to the expanded blastocyst stage and are transferred on day 5 after retrieval are approximately twice as likely to implant compared to those for which expansion and transfer are delayed until day 6.”

Although, interestingly, day 5 embryos are more likely to survive the thaw than day 6 (maybe because they tend to be higher quality?):

http://fertstertforum.com/kovalevskyg-blastocyst-frozen-embryo-transfer/

“A total of 1,406 embryos were thawed with a survival of 90.7% for day 5, 83.7% for day 6, and 78.7% for day 7. Implantation rates were 43.3%, 28.9%, and 28.9%, respectively. Ongoing PRs were 43.9%, 32.9%, and 26.7%, respectively.”

This article makes no distinction between quality.  I’m guessing that the day 5 embryos tended to be better quality than the day 6s (as has been our experience).

So I guess I should not fret over the day 5 v. day 6 issue… and just continue fretting over their poor quality.