Ovum: the Facts on Egg Cells

Everyone who ever lived and ever will start off the same way: a sperm reached an egg cell and fertilized it. But even once you know that the egg cell, or ovum, is one of the two things you need to start a new life that still leaves some questions about it. What role does the egg play? How many do you get, and what defines egg quality? Let’s run through these and some other frequently asked questions about the ovum.

What is an ovum and what does it do?

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The ovum, or egg, is the female reproductive cell. Stored in the ovaries until they are released into the fallopian tubes at ovulation, they combine with a sperm cell to create a zygote – a single cell from which an embryo eventually a fetus will start to grow.

Until then, the primary oocyte exists inside a follicle – the bundle of cells that surround it in the ovaries. These are stockpiled in both of the ovaries – one on each side of the uterus. In response to hormones from the pituitary gland, about 20 of the ovarian follicles in either the left or right ovary “wake up” and start to mature into primary follicles.

These primary follicles measure just 0.03mm at the start of their development. Of these, most will die off – but one follicle will continue to mature until it reaches 2cm in size. This is the dominant follicle, and it contains the ovum that’s ripe for fertilization. During ovulation, this follicle bursts open and releases the ovum, which is then transported into the fallopian tubes. The egg lives for only 24 hours after this, but if sperm is present in the reproductive tract at the right time, fertilization can occur.

The ovum supply is set from birth

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A female fetus starts off with up to 7 million immature egg cells but after this supply has developed by around Week 20, no more are ever produced. By birth, this number has dwindled 1 to 2 million and by the time puberty starts and the menstrual cycle kicks in, that number is down to about 400 thousand.

That number might sound like a lot, but remember: 99.9% of these die off and never make it to ovulation, and only about 500 eggs are ever released over a woman’s lifetime. Approaching menopause around age 50, a further 30 to 40 oocytes are dying off every day. In other words, female fertility is finite.

How does age affect ovum quality?

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The ovarian supply ages alongside the woman. Eggs that were originally a neat sphere become distorted into an oval or elliptical shape, making it more difficult for sperm cells to fertilize them, or for fertilized egg to successfully implant into the uterus. In other words, there is a decline in egg quality.

However, it’s not as simple as “young eggs good, old eggs bad”. Factors such as environmental pollutants, hormone imbalance, poor diet, unhealthy lifestyle habits such as smoking, and even stress can negatively impact the quality of ovarian supply. Unfortunately, once an egg has gone bad, there’s no way to turn back the clock. This is why maintaining a healthy lifestyle has such an important role to play in preserving fertility.

Take care of yourself, take care of your eggs

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Your egg supply diminishes in quantity and quality as you age, and unfortunately there’s not anything you can do to stop that. It’s just the way female reproduction works. However, by maintaining good lifestyle habits now and as you get older, you’ll give yourself the best shot at maintaining your fertility for as long as possible.

Don’t let this stress you out if you’re not ready to have a kid yet – it’s okay to take things at your own pace. But, if you’re thinking of having children further down the track, taking care of yourself now is a great step to take.