Blastocyst number and pregnancy outcomes – what is the optimum for fertility success?

This study investigated if there is an association between blastocyst number (BCN) and pregnancy outcomes. They found that a BCN of up to 5 was associated with positive pregnancy outcomes.

In vitro fertilization (IVF) is a technique used to fertilise an egg in a laboratory. The fertilized embryo is allowed to grow until it becomes a blastocyst (BC). It can then be transferred to the uterus. This is called a fresh embryo transfer (Fr-ET). BCs can also be frozen and transferred at a later date. This is called a frozen embryo transfer (Fz-ET).

During ET, one or more embryos may be transferred. Embryos can be selected using preimplantation genetic testing for aneuploidy (PGT-A). This technique can reduce the chance of implanting embryos that are likely to fail. Techniques like PGT-A are only useful if there are multiple BCs to chose from. It is unclear if the number of available BCs (BCN) is associated with pregnancy outcomes. 

This study included 16,666 women that underwent Fr-ET. The BCN for each patient was examined. Positive pregnancy outcomes included clinical pregnancy (CP) and live birth (LB). Miscarriage (MC) was also assessed.

The average BCN was 3. The odds of achieving a CP increased by 18% for each additional BC. This was maximal in patients with 5 BCs. The odds of achieving LB increased by 17% for each additional BC.

More than 5 BCs was associated with a decrease in CP. The same effect was observed for LB. Each BC over 5 was associated with a 2% lower chance of CP and LB. There was no association between BCN and MC rates. These effects on CP and LB odds were even greater in patients over 35. 

The authors concluded that a BCN of 5 or less was associated with positive pregnancy outcomes.

This was a retrospective analysis. Some patient information was not available. More investigation is needed. 

If you have any concerns regarding infertility please consult with your physician.