Delayed Blastocyst Transfer

A blastocyst is a stage of embryo development. After fertilization, embryos should divide into four cells by day two, eight cells by day three, the morula stage (40 - 60 cells) by day four, and the blastocyst stage (80 or more cells) by day five to seven.

The above picture shows an advanced stage of blastocyst development. Notice the central fluid-filled cavity. The cells within the blastocyst have already differentiated into the inner cell mass (at seven o’clock) that will give rise to the fetus and the trophectoderm cells that will form the future placenta.

During a natural, non-stimulated ovulatory cycle, estrogen (estradiol) level peaks just before ovulation. It is this increase of estrogen that triggers ovulation and the start of progesterone production by the ovaries.

Progesterone production, in turn, begins a sequence of endometrial lining development. Since the onset of progesterone secretion is tied to ovulation, in natural, non-stimulated ovulatory cycles, embryos and the endometrial lining develop at the same matched rate.

High estrogen or progesterone levels

When ovaries are stimulated as in In Vitro Fertilization treatment, estrogen levels peak much higher than in non-stimulated cycles. In spite of the use of medications to suppress ovulation and premature progesterone production (i.e., Lupron, Ganirelix), some patients’ progesterone levels will increase prematurely.

This premature increase of progesterone triggers an accelerated development of the endometrial lining, causing desynchronization between the lining and the development of embryos. Transferring embryos under such circumstances would significantly reduce the probability of successful implantation.

At Bay IVF, we closely monitor your estrogen and progesterone levels during ovarian stimulation. If your estrogen or progesterone levels become too high, we will inform you and recommend freezing of all your embryos with a subsequent Frozen Embryo Transfer treatment cycle.

Endometrial lining thickness

We also monitor the thickness of your endometrial lining. If the lining is too thin, the probability of embryo implantation is reduced. Your embryos will be cryopreserved, and you will have a subsequent Frozen Embryo Transfer treatment cycle.

Slow developing embryos

Another common cause of delayed embryo transfer is "slow" developing embryos. If it takes six or seven days for the embryos to reach the blastocyst stage instead of the ideal five, you can still conceive with them, but their development is now out of synchrony with the development of the endometrial lining. All your blastocysts will be cryopreserved, and you will have a Frozen Embryo Transfer procedure at a later date.

You should expect close to 100% embryo survival of the cryopreservation-thawing process. The likelihood of successful implantation of vitrified-thawed embryos is the same as with a "fresh" embryo transfer.