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Optimizing Fertility: What Determines Egg and Sperm Quality?

Egg Quality and Female Fertility

Every woman has a finite number of eggs that are long made before she is even born. From birth, the number of eggs declines from 2 million to merely 400,000 by the time of her first period. On top of that, egg quality is also reduced with aging, with a sharp downturn after the age of 351.


So you might wonder, what do we mean by the quality of eggs?

It means that as a woman ages, the percentage of eggs containing genetic errors becomes much higher. By the age of 40, only half of the eggs contain normal genetic material!

Each month, an egg undergoes a phase of cell division known as meiosis during ovulation. This is when our genetic material, DNA, is halved in order to prepare for combining with the other half provided by the sperm. When things go wrong in this process, aneuploidy may occur, which is when too many or too few chromosomes end up in the mature egg. This could have dire consequences, including failure to fertilize, miscarriages and genetic disorders like Down syndrome. This is part of the reason why older women have a lower chance of pregnancy and a higher chance of miscarriage.

Is there a test for egg quality?

There is not a specific test for egg quality and a genetically abnormal egg is also unlikely to produce a viable embryo. However, sometimes the errors are not enough to prevent fertilization but lead to serious health problems for the baby. This is when you can conduct a preimplantation genetic testing in an in-vitro fertilization (IVF) cycle or postconceptional genetic testings during a pregnancy.

Can you improve egg quality and fertility?

Since age is the single biggest factor in determining a woman’s egg quality, improving fertility to a substantial extent would require some methods to reverse aging. Scientists have been trying to find such methods for a long time but there are currently no medications available for reversing the decline of egg quality. Nevertheless, a very recent study has provided some promising clues as to how this may be possible by pharmacologically elevating levels of a metabolic cofactor NAD+2. Therefore, having a medication that prevents egg quality decline may be a possibility in the future.

If you are already over 35 and are worried about getting pregnant or having genetic errors in your baby, Assisted Reproductive Technologies (ARTs) are often good alternatives. With a fertility clinic, you could have your eggs removed and fertilized in the laboratory in a standard IVF cycle. See our previous blog for the top 10 fertility clinics in New England. During IVF, multiple embryos will be created and screened for genetic abnormalities using preimplantation genetic tests. This way, the technologies could make it faster to fertilize and prevent the difficult decision of terminating a pregnancy in the case of unfavorable results obtained from post-conception genetic screenings.

Apart from age, a healthy lifestyle including balanced nutrition, exercise, and minimal stress can also help. For example, the use of alcohol can prevent ovulation and being under or overweight could disrupt the menstrual cycle. Smoking and exposure to pollutants are also considered toxins for eggs3.

Can you preserve fertility?

Since egg quality starts declining at an age that coincides with career development, preserving fertility by freezing eggs is becoming a popular solution. In a fertility clinic, you could undergo a full IVF cycle with your partner’s sperm to create embryos and freeze them for a later pregnancy, a procedure known as cryopreservation. Alternatively, you could retrieve and freeze eggs for later fertilization.

In summary, egg quality is mostly determined by age, meaning that we are racing against irreversible time for fertility. At the moment, the best strategy is to preserve fertility using embryo/egg freezing technology if you are 35 years old or younger. If you are older than 35, an IVF treatment, combined with preimplantation genetic tests are recommended. In addition, a healthy lifestyle always helps with your general health and wellbeing, including fertility! If all of these approaches fail and the sperm is determined healthy, you may consider using a donor egg from a young woman to complete the IVF and have a healthy baby. Zeta fertility offers matchmaking services that can assist you on this journey.

Sperm quality and male fertility

Male fertility and sperm quality present a very different picture where age does not affect them nearly as much. Instead, lifestyle factors are crucial for improving male fertility.


Both daily consumption and binge drinking are known to affect fertility. In fact, just one to five glasses of wine per week can affect fertility3. Heavy drinking could lead to reduced male hormone production and affect sperm production.


Smoking can damage sperm DNA and increase the chances of miscarriage and childhood cancers. Smokers are more likely to have low sperm counts and poorer sperm quality4.


Being overweight could also be detrimental to male fertility as a higher body mass index has been linked to decreasing sperm count and motility4.

Man swimming


A sedentary lifestyle is not a good idea for sperm health as sitting on testicles for a long time causes them to overheat and inhibits sperm production. Regular exercise not only prevents this problem but also helps with weight management4.

Frequent ejaculation

Regular sex or ejaculation 2-3 times a week makes sure that sperm is not stored in the testicles for too long. Sperm that has spent a prolonged time in the testicles may have damaged DNA and lower quality5.

Recreational drugs and steroids

Recreational drugs such as marijuana and steroid abuse can lower sperm quantity and quality5.

Healthy diet

Nutrition is a big deal for prospective fathers. A high-fat diet can modify the sperm epigenetic information, which may affect offspring health and transmit metabolic abnormalities in future generations6.

How do you find out your sperm quality?

If you are having trouble conceiving, a semen analysis is an easy way to find out whether you have normal sperm quantity and quality. This is a common procedure in fertility clinics. If there are indeed problems with your sperm, alternative treatments may be arranged, such as Intracytoplasmic Sperm Injection (ICSI).


1. American Society for Reproductive Medicine. Age and Fertility.

2. Bertoldo MJ, Listijono DR, Ho WH, et al. NAD+ repletion rescues female fertility during reproductive aging. bioRxiv 721985; doi:

3. Department of Health, Government of Western Australia. Fertility and Lifestyle.

4. Mayo Clinic. Healthy sperm: Improving your fertility.

5. IVF Australia. Male fertility predictor.

6. Fullston T, Ohlsson Teague EM, Palmer NO, et al. Paternal obesity initiates metabolic disturbances in two generations of mice with incomplete penetrance to the F2 generation and alters the transcriptional profile of testis and sperm microRNA content. FASEB J, 27(10); doi: 10.1096/fj.12-224048

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