Optimization of implantation in the in-vitro fertilization laboratory

Predictive factors for embryo implantation potential

In spite of recent improvements in IVF, pregnancy rates have not increased significantly and one of the major problems remains the high multiple pregnancy rate. Better criteria are therefore necessary to establish the viability of a transferable embryo. Early prognosis of the developmental fate of the oocyte would help in selecting the best embryos to transfer, but non-invasive selection at the oocyte stage (extracytoplasmic and intracytoplasmic morphology) has proved to be of little prognostic value. Recently, it has been shown that follicular vascularization appears to be predictive of oocyte developmental fate, making it a good first-step approach for selection. Observation of pronuclei patterns at the zygote stage appears to offer an additional prognostic tool, correlating well with IVF outcome. Morphological evaluation of the embryo at days 2-3 remains the most used and valid method of selection, even though it is not sufficient to select embryos with the higher implantation potential. Blastocyst culture is another possible strategy for selecting the best embryos with reduced risk of aneuploidies, though not all major chromosomal aberrations are excluded by prolonged in-vitro culture. In summary, selecting the best embryo for transfer is a decision that should be based on choices made during the different stages of assisted reproductive technologies.

Fundamentals of human embryonic growth in vitro and the selection of high-quality embryos for transfer

Knowledge of the nature of embryo growth, and the handling and scoring of quality in human embryos are significant aspects for embryologists in IVF clinics. This review describes the formation, growth and maturation of human oocytes, many aspects of fertilization in vitro, embryonic transcription during preimplantation stages, and the formation of polarities, timing controls, role of mitochondria and functions of endocrine and paracrine systems. Modern concepts are fully discussed, together with their significance in the practice of IVF. This knowledge is essential for the correct clinical care of human embryos growing in vitro, especially in view of their uncharacteristic tendency to vary widely in implantation potential. Underlying causes of such variation have not been identified. Stringent tests must be enforced to ensure human embryos develop under optimal conditions, and are scored for quality using the most advanced techniques. Optimal methods of culture are described, including methods such as co-culture introduced to improve embryo quality but less important today. Detailed attention is given to quality as assessed from embryonic characteristics determined by timers, polarities, disturbed embryo growth and anomalous cell cycles. Methods for classification are described. Approaches to single embryo transfers are described, including the use of sequential media to produce high-quality blastocysts. These approaches, and others involved in surgical methods to remove fragments, transfer ooplasm or utilize newer approaches such as preimplantation diagnosis of chromosomal complements in embryos are covered. New outlooks in this field are summarized.

Birth weight and sex ratio after transfer at the blastocyst stage in humans

OBJECTIVE

To analyze the birth weights and sex ratio of infants born after blastocyst transfer.

DESIGN

Retrospective analysis.

SETTING

Three infertility clinics.

PATIENT(S)

Patients admitted for IVF with blastocyst transfer.

INTERVENTION

None.

MAIN OUTCOME MEASURE(S)

Birth weights and sex ratio of infants born after blastocyst transfer.

RESULT(S)

Statistically significantly more male infants were born after transfer of fresh blastocysts, either cocultured or cultured in sequential media. No specific differences in birth weight were observed between infants born after blastocyst transfer and those born after spontaneous conception.

CONCLUSION(S)

More male infants than female infants were born after blastocyst transfer when transfers were performed as soon as the blastocyst stage was reached and male embryos had a faster cleavage rate.

Successful use of a laser for human embryo biopsy in preimplantation genetic diagnosis: report of two cases

PURPOSE

The use of Tyrode's acid to drill the zona pellucida for embryo biopsy is the most widely used methodology in preimplantation genetic diagnosis. Instead of this, we propose the use of a 1.48-micron diode noncontact laser, which is quicker, simpler, and safer.

METHODS

The laser beam was tangentially guided to the zona pellucida of the embryo. Depending on zona pellucida measurement, two to four consecutive shots of 8-22 msec were necessary to drill the zona pellucida of the 13 embryos biopsied for two patients (hemophilia carriers).

RESULTS

Female embryos were replaced into the uterus of the patients (1.5 embryos/replacement). One single pregnancy was established (33.3% implantation rate). Coculture of untransferable embryos showed a blastocyst rate of 66.7% (4/6) for male embryos and 25% (1/4) for abnormal ones.

CONCLUSIONS

These results demonstrate the safety and usefulness of laser methodology in preimplantation genetic diagnosis.

Laser blastocyst biopsy for preimplantation diagnosis in the human

A new methodology for blastocyst biopsy that uses a 1.48 microm diode laser is described. Trophectoderm cells are biopsied after laster zona drilling and culture, fixed and processed for fluorescent in situ hybridisation (FISH) analysis. Preliminary results on the efficiency of the procedure and blastocyst recovery rate are promising. Blastocyst laser biopsy is a useful tool in preimplantation genetic diagnosis (PGD) as it allows a more reliable diagnosis and widens the diagnostic possibilities on account of the higher number of cells obtained in the biopsy.