Increased risk factors with blastocyst transfer vs cleavage stage

Researchers in a 2020 study found that blastocyst stage embryo transfers are associated with increased obstetric and perinatal risks.

The researchers looked at all IVF births from 1997 to 2015, encompassing about 52000 cleavage stage transfers and 4600 blastocyst stage transfers, in Denmark, Norway and Sweden. That’s a lot of embryos! All were fresh transfers (no frozen).

Here’s a breakdown of what they found when they compared the blastocyst transfers to cleavage stage:

• Placenta previa increased (4.1% vs 1.8% for blastocyst transfer vs cleavage stage)
• C-section increased (27.0% vs 25.8%)
• Induction of labor decreased (18.8% vs 19.2%)
• Preterm birth increased (8.3% vs 7.9%)
• Male sex increased (53.8% vs 51.0%)
• Twinning after single embryo transfer increased (1.9% vs 0.9%)

So what is it about blastocyst culture that’s leading to more complications?

The authors think that extended culture (from 2-3 days for cleavage stage to 5-7 days for blastocyst) might interfere with implantation and placentation. By transferring the embryo later, it will potentially have less time to “communicate” and interact with the endometrium and this might compromise their synchronization. Extended culture might also expose the embryo to more stressors, like temperature differences or alterations in pH and oxygen, that could impact gene expression.

The authors of this paper point out that other studies have been done that looked placental complications and blastocyst transfer and they found no association, although these were smaller studies.

Other studies that examined perinatal outcomes seem to be in line with their findings.

Reference

Spangmose AL, Ginström Ernstad E, Malchau S, Forman J, Tiitinen A, Gissler M, Opdahl S, Romundstad LB, Bergh C, Wennerholm UB, Henningsen AA, Pinborg A. Obstetric and perinatal risks in 4601 singletons and 884 twins conceived after fresh blastocyst transfers: a Nordic study from the CoNARTaS group. Hum Reprod. 2020 Apr 28;35(4):805-815. doi: 10.1093/humrep/deaa032. PMID: 32294185.

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About Embryoman

Embryoman (Sean Lauber) is a former embryologist and the founder of Remembryo, an IVF research and fertility education website. After working in an IVF lab in the US, he returned to Canada and now focuses on making fertility research more accessible. He holds a Master’s in Immunology and launched Remembryo in 2018 to help patients and professionals make sense of IVF research. Sean shares weekly study updates on Facebook, Instagram, and Reddit regularly. He also answers questions on Reddit or in his private Facebook group.

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