The concept of a female’s egg quality is derived from an observation that the probability of embryo implantation is associated with the age of the woman who provides the egg as well as her overall ovarian reserve. Egg quality is synonymous with embryo implantation.
Egg quality cannot be determined by merely examining the egg, nor by measuring its receptivity to fertilization by sperm. Even though an embryo appears good quality in the laboratory, it does not guarantee that it will implant in the uterus. The proof of good egg quality is ability for the developed embryo to implant in the uterine lining.
Diminished Ovarian Reserve
A woman with elevated follicle-stimulating hormone (FSH) levels on the third day of her menstrual cycle (menses) has a diminished ovarian reserve. This means that the ovaries are producing less feedback signals to the pituitary gland, and the woman’s body responds by making more FSH in order to stimulate the ovaries. Over the last decade, fertility centers have noticed that women with elevated FSH levels also have decreased egg quality, and these women rarely conceive using their own eggs. However, eggs retrieved from women with high FSH levels appear normal, fertilize normally, and can undergo initial embryo cleavage at a normal rate.
Advanced Maternal Age
When FSH levels are normal, the age of the woman providing the eggs will play a key role in determination of egg quality. Just as women with elevated FSH levels, eggs from women in their 40s appear normal and fertilize regularly. While the initial embryonic cleavage occurs in a normal manner, the embryos almost never implant. Because advanced maternal age contributes to infertility, the woman should not attempt use of own eggs unless FSH levels are normal.
Diminished Egg Quality
Egg quality can be explained using the battery analogy. Consider that each egg has a number of batteries that offer energy stores. The batteries are analogs of mitochondria, which produce energy in mammalian cells. As a woman ages, the energy-producing ability of mitochondria declines. Before ovulation, the egg is connected to the circulation, and it is connected again following embryo implantation.
The egg and resulting embryo is dependent on mitochondria energy at the moment of ovulation until implantation.
Older eggs may appear normal at the time of ovulation and embryo development, but this is because its energy stores are still good. However, once the egg runs out of batters, and no longer divides, implantation can be achieved. This is because the embryo quits dividing right before the implantation stage. When egg quality is low, the only proven treatment that will bring about reliable results is egg donation.
Clomiphene Citrate Challenge Test (CCCT)
The most sensitive tested used to evaluate ovarian reserve is the clomiphene citrate challenge test (CCCT). Clomiphene citrate (Serophene or Clomid) is used for ovulation induction in fertility treatment. Before the therapy, the woman’s estrogen level (estradiol) and FSH level are measured. The woman takes the oral medication for five days. The test can prove if or not the woman can conceive and maintain a successful pregnancy.
Basal Follicle Count
Another test used to measure ovarian reserve is the basal follicle count. The doctor uses ultrasound technology to count the woman’s small follicles on the ovaries. A low number of follicles indicates that therapy will not be promising and a lower chance of conception and pregnancy. However, high numbers of small follicles show a tendency for the woman to over-respond to stimulation of hormones.