THE EFFECT OF OOCYTE QUALITY ON INFERTILITY, EMBRYONIC DEVELOPMENT AND ADULT LIFE

Oocyte quality affects early embryonic survival, the establishment and
maintenance of pregnancy, fetal development, and even adult disease.

Poor oocyte quality is the cause of infertility in a significant number
of couples unable to conceive. In Europe, about 15% of women of childbearing
age have received infertility or assisted reproduction treatment.
Unfortunately, 69% of in vitro fertilization (IVF) cycles do not result in pregnancy.

Oocyte quality affects maternal and
infant morbidity. Poor oocyte quality is associated with many conditions such as  micronutrient deficiencies, increased maternal
age, thyroid or other endocrine problems, autoimmune diseases or other
conditions that affect immunity, metabolic syndrome, diabetes and syndromes or
conditions that influence fertility such as Polycystic Ovary Syndrome (PCOS)
Pelvic Inflammatory Disease (PID) or Endometriosis. All of the above, are
manifested by specific changes in metabolic pathways that may affect
conception, implantation, embryonic development and pregnancy outcome.

Women that produce low quality oocytes are more likely to suffer from
maternal complications during pregnancy such as hypertention (high blood
pressure) during pregnancy, preeclampsia, eclampsia, increased likelihood of
caesarean section, venous thromboembolism, postpartum hemorrhage, thyroid
dysfunction and gestational diabetes. In such cases there is an
increased risk of miscarriages, low birth weight
and/or prematurity and newborns with long term disabilities such as cerebral
palsy, deafness, and visual impairment.

Furthermore, adult phenotypes and embryonic characteristics, are largely
defined by the quality of the oocytes from which they are derived and are
related with metabolic and mental diseases in adulthood and numerous conditions
such as increased body mass, altered immune responses to antigenic challenge,
insulin resistance, thyroid dysfunction and elevated blood pressure that
persist throughout life and may lead to obesity diabetes and even cancer.  

The oocyte provides the essential life-generating force for combining
gametes to create a new, functional, and viable individual.

The oocyte is uniquely endowed with the ability to combine its own
components with those of the incoming sperm, and direct the creation of a
functional embryo. The oocyte is a highly differentiated, molecularly complex
product of gametogenesis, despite its outwardly simple morphological
appearance. During oogenesis, the oocyte must accumulate the components that
are needed to support early embryo metabolism and physiology, as well as
components needed to complete meiosis, initiate cell cycle progression, and
direct early developmental events, such as the establishment of the primary
embryonic body axes. The oocyte must combine the two haploid genomes into a
single embryonic genome, activate transcription of that genome at the correct
time, and activate the appropriate array of genes to be transcribed.
Additionally, the oocyte must maintain essential epigenetic information, while
simultaneously remodeling chromatin and modifying certain other kinds of
epigenetic information. In short, the successful development of all embryos is
predicated upon correct and efficient execution of many crucial processes by
the oocyte to create a functional embryo.

The oocyte is a unique and highly specialized cell responsible for
creating, activating, and controlling the embryonic genome, as well as
supporting basic processes such as cellular homeostasis, metabolism, and cell
cycle progression in the early embryo. During oogenesis, the oocyte accumulates
a myriad of factors to execute these processes. Oogenesis is critically
dependent upon correct oocyte-follicle cell interactions. Disruptions in
oogenesis through environmental factors and changes in maternal health and
physiology can compromise oocyte quality, leading to arrested development,
reduced fertility, and epigenetic defects that affect long-term health of the
offspring.

Many aspects of oogenesis, oocyte biology, and oocyte components are
responsible for creating a healthy, functional embryo. Where these processes
are disrupted, the result is poor quality oocytes that are deficient in
supporting correct embryo development. Recent discoveries link maternal
nutrition to defects in organogenesis and physiology in adult stage offspring.

The oocyte contains a rich supply of macromolecules and organelles that
collectively support and regulate vital processes in the early embryo. This
includes processes such as ion homeostasis, metabolism, cell cycle progression,
DNA repair, apoptosis, transcriptional activation of the embryonic genome,
epigenetic modifications and reprogramming of the genomic material, and in some
species early cell fate determine events that control subsequent morphogenesis
and differentiation.

Quality, or
developmental competence of the oocyte, is acquired during folliculogenesis as
the oocyte grows, and during the period of oocyte maturation.

The oocyte is endowed with a rich legacy of proteins, mRNAs, and other
macromolecules that direct and regulate early development. This legacy arises
through essential biosynthetic processes that are directly affected by
interactions with the follicular environment. Disruptions in these interactions
can compromise oocyte quality. The creation of high-quality oocytes is thus
sensitive to genetic and environmental factors.

Dr. Dimitrakopoulos K. Ioannis MD, PhD, OB/GYN

Ιωάννης Κ. Δημητρακόπουλος 

Μαιευτήρας - Γυναικολόγος

Ιατρείο: Λεωφ. Δημητρίου Γούναρη 196  Γλυφάδα Τ.Κ. 166 74

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