Oocyte quality is one of the key factors when it comes to achieving pregnancy. For the fertilization, implantation, and development of the embryo to take place, it is essential to have eggs of good morphological and genetic quality.
Low oocyte quality is one of the main causes of female infertility and this is directly related to the women’s age.
From 35 years on, the quantity and quality of eggs begin to decrease considerably. However, it must be kept in mind that both concepts are not the same, as having a good number of oocytes does not imply that they will be of good quality.
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Egg quantity vs. Egg quality
The woman's ovarian reserve, i.e. the number of eggs she will have throughout her reproductive life, is already established from the moment of birth. Girls are born with between 1 and 2 million immature eggs, Approximately. However, by the time they hit puberty, this ovarian reserve has already decreased to 500,000 oocytes.
From this moment on, the woman will release a mature egg in each menstrual cycle, while many others will undergo a process called atresia and will be lost.
All this shows how a woman's ovarian reserve gradually decreases over time until it is completely exhausted when she reaches menopause. However, not only does the number of eggs decrease with age, so does their quality. As they age, the eggs accumulate mutations in their DNA, which can lead to defective embryos that end up in abortion or the birth of a sick baby.
Just because a 40-year-old woman has a good number of antral follicles seen by ultrasound, that is, her ovarian reserve is good, does not automatically mean that all these eggs will develop normally or will be of good quality.
The age of the woman is essential for maturing eggs to be of good quality. From the age of about 35, the quality of the eggs will worsen and decrease, too.
Oocyte quality analysis
Today, there are several diagnostic tests to evaluate the state of a woman's ovarian reserve, such as an antral follicle count by ultrasound, antimullerian hormone analysis, or determination of blood FSH levels.
However, knowing the quality of the eggs is not so easy. In IVF treatments, there is no proof that the recovered oocytes have chromosomal alterations. The only viable option would be to fertilize them and then make a preimplantation genetic diagnosis (PGD) of the embryos generated.
On the other hand, during IVF treatment it is possible to evaluate the morphology of the eggs under a microscope, although the alterations in their structure in principle have no relation to the genetic alterations. As the next step, we will comment on what a normal oocyte would look like and what oocyte dysmorphisms might be found during its evaluation.
What does a normal egg look like?
An oocyte must have a rounded shape and, in addition, have all of the following structures correctly defined:
- A homogeneous cytoplasm, with no foreign body to attract attention inside
- A single polar body in the perivitelline space (EP), slightly flattened and of homogeneous content
- A perivitelline space that is hardly perceptible, only in the zone where the CP is
- A uniform Zona Pellucida (ZP) of suitable thickness
The presence of the first polar corpuscle indicates that the egg has reached nuclear maturity and is therefore suitable for fertilization. Mature oocytes are said to be in metaphase II.
Cytoplasm alterations
As we have said, the egg must be spherical and its cytoplasm must be completely regular with no structure inside.
Some alterations that we can find in the cytoplasm are the following:
- Granular content
- Refringent bodies
- Necrotic bodies with granular content
- Smooth endoplasmic reticulum (opaque and large) and vacuoles (round and transparent)
- Cluster: granular and dark area in the center of the oocyte
Polar body alterations
A mature ovum has a single polar body, round and elongated, and perfectly delimited. The alterations that may appear in the oocyte referring to polar body are the following:
- Multiple polar bodies, i.e. there is more than one
- Fragmented polar body
- Amorphous or very flat polar body
Periviteline space alterations
The perivitelline space is the space between the zona pellucida (outer layer) and the oocyte itself. A perivitelline space that is hardly perceptible, only in the zone where the polar body is, Therefore, the alterations referring to the perivitelline space are the following:
- Wide perivitelline space or with irregular wide and narrow areas
- Presence of cellular debris in the perivitelline space
Zona pellucida alterations
The zona pellucida is the outer layer that surrounds the egg. It should have a proportionate amplitude of about 15-20 microns.
The alterations that can be found in the ZP of an oocyte are the following:
- Too thick or too narrow amplitude
- Loose (light) or too dense (dark) ZP
- Irregular ZP, with areas thinner than others
- Rugged inner zone
- Divided ZP forming an independent section
- Elongated ZP
All these dysmorphisms can make it difficult to fertilize the eggs, although with intracytoplasmic sperm injection (ICSI) it is possible to fertilize them as well.
It is also possible that partitioned, elongated or too thick ZPs may cause problems when hatching, i.e. when the blastocyst-state embryo detaches from its zona pellucida to be able to implant into the endometrium.
In this case, the embryologist would consider the option of assisted hatching.
What are the causes for poor egg quality?
We have already commented that the advanced age of women is the main cause of poor oocyte quality, especially from the age of 35.
In addition, other pathologies or unhealthy habits can also have a harmful effect on the eggs. We will discuss them below:
- Endometriosis
- Polycystic ovary syndrome (PCOS)
- Tobacco and alcohol
- Poor eating habits
- Radio/chemotherapy treatments
Therefore, maintaining a healthy lifestyle, practicing sports, and avoiding the consumption of toxic substances will be the best prevention to not have the oocyte quality affected.
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FAQs from users
How is the quality of the eggs evaluated?
Knowing the quality of the eggs before undergoing fertility treatment is very complicated and there are no tests for this. What we can do is approximate the number of eggs we can expect. There are several tests, although the main ones are the measurement of the antimullerian hormone or the antral follicle count in an ultrasound scan. With these two tests, a gynecologist can give you an idea of your ovarian reserve.
The best way to check the quality of the eggs is through an in vitro fertilization cycle. This cycle allows direct observation of the response of the ovaries to hormonal stimulation. After the ovarian stimulation, the gynecologist will count the follicles that have a good size and are developed. After the extraction, the biologist observes the oocytes under the microscope and will analyze the quality according to their shape and the characteristics of their cytoplasm.
Several studies have shown that morphological alterations in the oocytes are associated with a worse pregnancy rate.
Read more
What foods should I include in my diet to get pregnant?
Fertility, among other things, depends on the health of each person, so food is one of the most important bases before and during pregnancy.
It is advisable to follow a healthy and varied diet. The Mediterranean diet is ideal for this, as it provides the necessary nutrients for a healthy lifestyle. In addition, you can eat as many times a day as necessary, but taking into account the appropriate amounts for each person.
Read more
What are the indicators of good egg quality?
Egg quality is one of the most important and probably least known aspects of assisted reproduction. Finding a morphologically normal egg does not guarantee the subsequent achievement of pregnancy, but it does allow the prediction of a high percentage of the embryonic evolution, always taking into account other aspects such as age or ovarian reserve. Thus, we can distinguish three types of indicators, gynecological, morphological, and embryonic.
Read more
How can I improve my egg quality?
First of all, it is important to make it clear that no miracle drug will improve the quality of the eggs. However, healthy lifestyles and a healthy, balanced diet can indeed help boost female fertility.
Foods rich in vitamins, antioxidants, and essential nutrients are those that cannot be missing from the diet. For example green leafy vegetables such as spinach, nuts such as walnuts, legumes such as lentils, fish such as salmon and light tuna, fruits and vegetables such as blueberries, avocado, pomegranate, pineapple, carrots, and so on.
Related post: What should I eat to get pregnant?
Does the Anti-Müllerian hormone measure egg quality?
No. The antimüllerian hormone (AMH) indicates the number of antral and preantral follicles in the ovaries. It is, therefore, an indirect measurement of the ovarian reserve.
AMH levels between 0.7 and 3.5 ng/ml are considered normal, while levels below 0.7 ng/ml are associated with a decreased ovarian reserve.
Does vitamine E boost egg quality?
Yes, specifically what vitamin E does is protect the eggs from suffering alterations. Vitamin E also prevents changes in a woman's menstrual cycle.
Foods rich in vitamin E that contribute to oocyte quality are avocado, almonds, hazelnuts, walnuts, olive oil and sunflower oil, spinach, etc.
Suggested for you
We talked about the ovarian reserve and its close relationship with the quality of the eggs. If you want to continue reading about this subject, do not hesitate to access the following article: How many eggs does a woman have? Your egg count by age
Besides, to evaluate the morphological quality of the eggs, an IVF-ICSI treatment is necessary. You can find all the information about this technique and how it is done step by step in the following article: What is ICSI technique? Process, success rates & cost
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References
Remohí, Bellver, Ferrando, Requena, Pellicer. Manual práctico de Esterilidad y Reproducción Humana. Aspectos clínicos. 5ª edición. Editorial Médica Panamericana.
Romero JL, Gámiz P, Florensa M, Zulategui JF, Remohí J, de los Santos MJ. La morfología ovocitaria y su distribución en pacientes sometidas a hiperestimulación ovárica controlada. In Remohí J, Cobo A, Romero JL, de los SantosMJ, Pellicer A (eds) Manual Práctico de Esterilidad y Reproducción Humana. Laboratorio de reproducción asistida. 2008. Editorial McGraw-Hill / Interamericana de España, S.A.U. 3ª edición, pp.139 - 149.
Sociedad Española de Fertilidad (SEF). Clasificación y cultivo de los ovocitos (ver)
FAQs from users: 'How is the quality of the eggs evaluated?', 'What foods should I include in my diet to get pregnant?', 'What are the indicators of good egg quality?', 'How can I improve my egg quality?', 'Does the Anti-Müllerian hormone measure egg quality?' and 'Does vitamine E boost egg quality?'.
