A little studied aspect of developmental arrest (DA) in ART is zygote arrest (ZA). Etiologically, blockage at the first cleavage stage includes molecular and chromosomal anomalies, some of which manifest morphologically. Given considerations on embryo culture, transfer and cryopreservation, optimal zygote selection is very important. The aim of this study was to ascertain whether zygote morphological features were indicators of increased ZA. In this study we performed a prospective, observational study of 2105 zygotes obtained from consecutive patients who were undergoing IVF/ICSI treatment, of which 43 (2%) suffered ZA. Morphological features observed under the inverted microscope were qualitatively categorized: pronuclear size, nucleolar precursor bodies (NPB) alignment, light and dark halos, polar body placement and fragmentation observed at 16-18 h post-insemination. We compared these features in blocked versus cleaved zygotes at 48 h and found significant correlations (p < 0.05) between ZA and three features: the absence of a light halo (p = 0.001), the absence of a dark halo (p < 0.005), and non-aligned NPB (p < 0.05). We can say that certain morphological features are indicators of significantly increased zygote arrest. These findings may be of utility for optimal zygote selection and culture strategies, especially in countries under restrictive conditions.

SummaryHLA-G expression has been detected in early preimplantation embryos and it has been postulated that a relationship between embryonic expression of this factor and successful pregnancy may exist. Forty-six patients were prospectively selected from our centre ‘Unidad de Reproducción Humana, Hospital Universitario de Canarias’ for conducting this study. In all cases, metaphase II (MII) oocytes were fertilized using intracytoplasmic sperm injection 2–4 h after retrieval. Embryos were cultured individually in 20 µl droplets of G-1 medium (VitroLife) under oil at 37°C and a 6% CO2 environment. Fertilization was assessed at 18 h postinsemination and all oocytes fertilized were passed into a new culture plaque individually in 300 µl culture medium until day 3 of culture. The culture medium was examined for the expression and secretion of sHLA-G with a sandwich enzyme-linked immunosorbent assay kit (BioVendor, Heidelberg, Germany) according to the manufacturer’s instructions. We found statistical significance between higher levels of sHLA-G secretion and pregnancy rate. When both groups were compared there was no difference in embryo quality of transferred embryos, but a significant difference in the number of oocytes and the embryo quality of the cohort existed that was greater in the pregnant group. A standardized sHLA-G assay with a specifically defined range and standard units provides a non-invasive method to identify the most competent embryos for transfer.

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