Natural Causes for Low Human Fertility

Review Article

Austin J In Vitro Fertili. 2014;1(2): 5.

Natural Causes for Low Human Fertility

Delimitreva S*, Zhivkova R and Markova M

Department of Biology, Medical University of Sofia, Bulgaria

*Corresponding author: Delimitreva S, Department of Biology, Medical University of Sofia, 2 Zdrave St, 1431 Sofia, Bulgaria

Received: October 08, 2014; Accepted: October 27, 2014; Published: October 29, 2014


Despite the efforts to improve the conditions of gamete and embryo culture, the success rate of assisted reproductive techniques in humans is limited. This suggests that the reduced embryo potential could not be a result only of suboptimal in vitro conditions, but real features of oogenesis and early embryogenesis are involved. Low developmental potential of embryos is related to high rate of chromosomal abnormalities. The chromosomal segregation errors are based on disturbance of interactions between chromatin, cytoskeleton and other factors involved in the last stages of mammalian oocyte meiosis.

Keywords: Mammalian oocyte; Meiosis; Preimplantation embryo; In vitro fertilization; Aneuploidy


IVF: In Vitro Fertilization; IVM: In Vitro Maturation; ART: Assisted Reproductive Techniques; aCGH: Array Comparative Genomic Hybridization


Studies on early mammalian embryogenesis started with the work of Carl Hartman. In 1931, he published his observations on bovine preimplantation embryos obtained by oviductal flushing [1]. Later, a similar approach was applied to obtain oocytes and preimplantation embryos from other mammalian species with easily predictable or controllable oestrus with multiple ovulations - rabbits, rodents and ungulates [2-5]. The techniques of human IVF (in vitro fertilization) were based on these investigations. Studies of mammalian oocytes and preimplantation embryos became the base for development of assisted human reproduction, as well as for fundamental investigations of human oogenesis and early embryogenesis.

Limited Success Rate of IVF

In vitro fertilization was developed as an approach for treatment of human infertility. However, its introduction was soon followed by disappointment of the relatively limited success rate of the method. It was initially assumed to be a result of suboptimal conditions of in vitro culture systems, hormonal stimulation and techniques for oocyte aspiration. Hence, efforts for improving success rates were directed towards optimization of these factors. A major step in the development of ART (assisted reproductive techniques) was provided by the introduction of gamete manipulations. As a result of their application, the success rate of ART was brought close to that of natural conception-according to current official data of ESHRE, the success rate of ART in European clinics is approximately 30%, and this proportion has remained stable [6,7]. Moreover, even this rate is due to the fact that in each treatment cycle, typically 2 or 3 embryos were transferred into the uterus. Now, it is accepted that the chance for each embryo to be implanted is approximately 15% [8,9]. These facts indicate that the potential to improve the success rate of ART, though not yet exhausted, is limited. Hence, the decisive factor for the treatment success must be some natural characteristics of the embryo.

Morphological Defects of Preimplantation Embryos

The most obvious abnormality of human IVF embryos is the high rate of morphological disorders - cell fragments, differences in blastomere size, enucleated and multinucleated cells, apoptotic-like cells and inadequate blastomere number are observed in more than half of the embryos [9-12]. These data can be summarized in Table 1. For the last decade, elaboration of culture and manipulation techniques has not brought significant improvement of these data.

Citation: Delimitreva S, Zhivkova R and Markova M. Natural Causes for Low Human Fertility. Austin J In Vitro Fertili. 2014;1(2): 5. ISSN:2471-0628