Life Cycle of a Human Egg

At The Positive Birth Company, we love to jump on a seasonal trend, so this weekend we have to speak about eggs! Not the chocolate variety, but the ones we are born with. So let’s go back to school for a biology lesson from our Resident Midwife. If you didn’t pay attention then, but are thinking about trying to conceive, read on!

Women are born with all their egg cells inside their ovaries (so they will also have been carried by the maternal grandmother – very clever stuff). Each woman can carry up to 7 million eggs and these will be released with every menstrual cycle through the woman’s lifetime. A human egg cell is the largest cell in the body, it is also the only human cell that is visible to the naked eye and does not need to be viewed under a microscope to be seen.

The entire menstrual cycle is regulated by hormones. Throughout the first stage of the menstrual cycle the hormone oestrogen increases in your body to help your ovaries to release an egg. Most women release an egg (or sometimes 2!) every menstrual cycle. This phase of the cycle is called ovulation. The egg travels from the ovary through the fallopian tubes and towards the womb. The womb lining also starts to thicken, with the help of progesterone, to support and prepare for the implantation of a potentially developing embryo.

When can you get pregnant?

Once the egg has been released it has a very short life-span and only survives for 12-24 hours (this is referred to as your fertile window). Sperm, however, can live up to 7 days in the female genital tract – so the time to try and conceive is often a day or 2 ahead of ovulation, or sometimes even earlier than that. Tracking your cycles and bodily changes along with ovulation can be really useful when trying to conceive – there are plenty of apps available to download that make cycle tracking very straightforward. It is very difficult to pinpoint exactly when ovulation happens but it is believed to be around 10-16 days before the next period. This can often be seen visibly by a change in vaginal discharge. It can become clearer, thinner and more stretchy – a bit like raw egg white.

If the egg is fertilised on its journey through the fallopian tubes, it will quickly begin to develop into an embryo and once it reaches your womb it will implant in the thick lining, creating the very early foundations of a baby – and quite possibly already giving you some very early pregnancy symptoms.

If the egg is not fertilised on this journey it is reabsorbed into the body. Consequently, levels of oestrogen and progesterone fall and the womb lining along with some blood is passed, as a period, through the vaginal tract. The first day of your period counts as day 1 in your menstrual cycle, and the process starts over. Periods usually last between 2 and 7 days and in a normal period you are likely to lose anything between 20ml and 90ml of blood.

The average length of the menstrual cycle is 28 days, however anything ranging from 23 to 35 days is considered normal. Females can start their periods as early as 8 years old, with the average age being around 12. The average age for menopause is 51 (https://www.nhs.uk/conditions/periods/fertility-in-the-menstrual-cycle) – that is as many as 480 menstrual cycles or periods in a lifetime!

How does contraception work?

It is important to bear in mind that if you are on contraception, then many of these methods work by supressing ovulation and therefore your body is stopped from releasing an egg for that cycle. If you continue to have regular cycles but do not ovulate (release an egg), this is called an ovulatory cycle. It is also important to note that taking hormonal birth control does not delay menopause or preserve eggs. While it may stop you releasing an egg, it does not preserve it. Unused eggs deteriorate overtime in your system.

For more information on ovulation, menstrual cycles and fertility please visit the NHS website - https://www.nhs.uk/search/results?q=menstrual%20cycle.