Embryo development and chromosomal anomalies after ICSI: effect of the injection procedure.

Intracytoplasmic sperm injection (ICSI) is a delicate procedure requiring considerable skills of the person performing it. Theoretically, the injection procedure could damage cytoplasmic structures in the oocyte, resulting in sublethal cellular injury and/or numerical chromosomal abnormalities that could lead to impaired embryonic development. In the present study, features of the injection procedure were evaluated in a total of 2924 oocytes from 305 cycles. Development to the blastocyst stage was found to be compromised in a group of surplus embryos originating from oocytes in which >6 pl of cytoplasm was aspirated into the injection pipette during the ICSI procedure. Characteristics of the injection procedure as well as blastocyst development of surplus embryos was shown to be significantly different between the four technicians performing the ICSI. Neither the volume of cytoplasm aspirated during the injection procedure, nor the position of the polar body (6 o'clock or 12 o'clock) influenced the mean incidence of disomic cells per blastocyst as revealed by fluorescence in-situ hybridization using probes specific for chromosomes X, Y and 18. In conclusion, certain technical aspects of the injection procedure can affect subsequent embryonic development to the blastocyst stage, but do not seem to influence the rate of chromosomal abnormalities that occur in human pre-implantation embryos.

Effect of oxygen concentration on in vitro fertilization and embryo culture in the human and the mouse.

OBJECTIVE: To compare the effect of culturing oocytes, zygotes and embryos under low (5%) versus ambient (20%) oxygen conditions on human IVF results and on mouse blastocyst formation. DESIGN: A prospective, randomized study of 257 consecutive IVF treatment cycles in 186 couples undergoing oocyte retrieval for various reasons of infertility. Gametes and resulting embryos after IVF were alternately allocated to fertilization and culture either under a gas phase of 5% CO2/90% N2/5% O2, or 5% CO2/95% air (20% O2). Oocytes and embryos from randomly bred and hybrid mouse strains were randomly allocated to culture under either of the two gas phases. SETTING: A university hospital-based IVF-ET program. MAIN OUTCOME MEASURE: In the human, rates of fertilization, embryonic development at the time of embryo replacement (42 to 46 hours after insemination), pregnancy, and implantation were compared. In the mouse, the rates of blastocyst formation were compared. RESULTS: Clinical pregnancies occurred in 24.2% versus 19.4% of retrievals when culture took place under low oxygen versus ambient oxygen conditions. Fertilization, embryonic development, pregnancy, and implantation rates did not differ significantly between the groups. Slightly higher blastocyst rates occurred when mouse embryos from hybrid strains were cultured under low oxygen compared with culture under ambient oxygen conditions, whereas no such difference in blastocyst rates was found in randomly bred mouse embryos. CONCLUSIONS: This study failed to demonstrate any improvement in human IVF results associated with the use of a gas mixture of 5% CO2/90% N2/5% O2 during the first two days of development compared with the use of 5% CO2 in air.

Triploidy after in vitro fertilization: cytogenetic analysis of human zygotes and embryos.

Tripronuclear zygotes obtained from a clinical IVF program were studied cytogenetically. Successful analysis was possible of 42 specimens at the zygote stage and 21 embryos after the first or second cleavage division. In the majority of zygotes (88%) the expected triploidy was confirmed, whereas only 14% of embryos had solely triploid cells. Therefore it is concluded that after tripolar cleavage division, many different types of mosaicism may originate from irregular chromosome distributions. Since the findings in individual blastomeres in embryos resulting from multipronuclear zygotes do not reflect the genetic content of the whole embryo, these embryos are less suitable in a model system for preimplantion diagnosis. The distribution of the sex chromosomal types (XXX, XXY, and XYY) confirmed theoretical expectations. Since in abortion material or in liveborn triploidy cases, the XYY karyotype is hardly ever observed, this indicates that most likely the 69,XYY karyotype has a very high embryonic mortality.