Does blastocyst transfer weed out chromosomally abnormal embryos?

• Many human embryos are chromosomally abnormal
• As female age advances, the rate of chromosomal abnormalities in eggs increases substantially
• At 30 years old approximately 30% of eggs (and embryos) are chromosomally abnormal
• By age 37 the average rate of chromosomal abnormality is 45%
• 75% of embryos are abnormal by age 42, and 90% by age 44

Some studies have shown that there is a higher percentage of chromosomal abnormalities in day 3 embryos than in day 5 embryos.

• This is because chromosomally abnormal embryos are more likely to arrest during early development compared to chromosomally normal embryos
• Therefore, day 5 embryo transfer has a filtering effect – weeding out some of the chromosomally abnormal embryos
• Unfortunately, many chromosomally abnormal embryos form good looking blastocysts
• To do more reliable screening for chromosomally abnormal embryos we can do preimplantation genetic screening – PGS
• PGS is done by biopsying day 5 or day 6 blastocysts and performing chromosomal testing on the biopsied cells
• The embryos are frozen after the biopsy and transferred later after genetic test results are back

 

Risks for multiple pregnancy with blastocyst transfers

One of the greatest benefits of blastocyst transfer is the potential to reduce the risk of multiple pregnancy by transferring fewer embryos of higher quality. We have had a very low percentage of triplet (or higher order) pregnancies from blastocyst transfer at our clinic.

• The rate of triplets with blast transfers at our IVF center has been about 2% of pregnancies.
• These triplets have almost always been due to “identical twin” splitting of an embryo
  • 2 transferred and 3 implanted, after one of the embryos has split into 2

 

Regarding day 6 blastocyst transfer statistics

In the early years of blastocyst transfer (1998 and 1999) we sometimes looked at embryos early on day 5 and had patients with slower embryo development come in on day 6 for their transfer. For example, patients with only morula stage embryos and no true blastocysts yet.

• We thought it was better to let those slower embryos develop and expand more in the culture dish before choosing the best 1 or 2 for transfer.

However, success rate statistics for day 6 blastocyst transfers were somewhat lower than we were seeing for 5 day transfers. We believe this is because some of the embryos that are “slower” on day 5 are weaker, poor quality embryos.

• Of course, the “slow” embryos that had blastocyst formation by day 6 and went on to expand, hatch, implant and make babies were strong and healthy all along – just slower starters.
• Remember the story about the tortoise and the hare?

Comparing day 5 and day 6 blastocyst transfers, we saw better success rates with transfers done day 5. However, this is mainly because patients with embryos developing at a more “normal” rate were getting embryo transfers done on the 5th day, not because transferring embryos on day 6 is bad for outcome.  


IVF blastocyst picture shows hatching out from the shell – at lower right of photo This blastocyst is grade 5AA After hatching, the embryo can invade and begin implantation in the uterine lining This picture was taken a few minutes prior to embryo transfer