The influence of zygote pronuclear morphology on in vitro human embryo development
Background: The selection of embryos with largest implantation potential is an important part in assisted reproduction. Besides the embryo or blastocyst morphology, selection criteria such as position and orientation of pronuclei (PN) in relation to polar body positioning and the number, size and distribution of nucleolar precursor bodies (NPB) have been proposed. In our study, a correlation between PN and NBP morphology with the development of early embryos (day 2 of cultivation) and blastocysts (day 5) was investigated.
Methods: 653 zygotes from 113 IVF (in vitro fertilization) and ICSI (intracytoplasmic sperm injection) patients, younger than 40 years, were assessed 18–20 hours post-insemination. Optimal zygotes (Z1) had thouching centrally located PN with equall numbers of alligned NPB. Other zygote types differred from Z1 in having scattered NPB in both PN (Z2) or alligned NPB in one PN (Z3) or in PN beeing distant from one another (Z4). For each zygote type a percentage of normal early embryos and blastocysts was calculated.
Results: Among 653 assessed zygotes 21.8 % were Z1; 29.1 % Z2, 34.6 % Z3 and 14.5 % Z4. The percentage of normal early embryos decreased from Z1 to Z4 zygote type (70.4 % vs. 55.3 % vs. 59.7 % vs.45.3 %; p < 0.05) as well as the percentage of developed blastocysts (63.4 % vs. 55.3 % vs. 58.8 % vs. 43.2 %). However, the percentages of optimal blastocysts in the four groups did not differ (11.3 % vs. 11.1 % vs. 8.4 % vs. 6.3 %).
Conclusions: Best grade zygotes result in batter early embryo and blastocyst development suggesting that zygote morphology can be used in combination with embryo and/or blastocyst evaluation as a method for embryo selection prior to embryo transfer.
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