OBJECTIVE:

It is well accepted that hatching blastocysts have the highest implantation potential provided that inner cell mass (ICM) and trophectoderm (TE) have formed adequately. Though there is a wide variety of possible hatching spots around the blastocyst surface, no data exist analyzing the actual influence of this site on implantation behaviour. This semi-prospective study was set up in order to evaluate if blastocysts implant at a higher rate, if the opening of the zona pellucida is located close to the ICM, which corresponds to the area that will later drive invasion into the endometrium (syncytiotrophoblast).

MATERIAL-METHODS:

During the initial phases of the study images of all transferred hatching blastocysts were checked if they herniated near the ICM (study group) or TE (control group). As soon as it became evident that blastocysts hatching close to the embryoblast were superior in terms of outcome they were selected prospectively.

RESULTS:

A total of 108 patients were involved, 82 of them had a homogeneous transfer in terms of the hatching site. Patients from the study group showed a trend towards a higher (P=0.06) clinical pregnancy rate (72.4%) as compared to the control group (50.9%). Implantation rate, however, was significantly increased (66.7% vs. 40.8%) (P=0.009).

DISCUSSION:

Theoretically, hatching at the embryonic pole could accelerate contact between those trophectodermal cells supposed to draw the blastocyst into the uterine wall and the endometrium.. This mutual interaction between blastocyst and uterus may be hindered or delayed if herniation takes place opposite the ICM and/or if hatching difficulties occur.

Keywords: blastocyst, hatching, inner cell mass, trophectoderm