The reproductive cycle of a female is a very interesting one. Just like other animals, a human child is produced when the female egg is fertilized by the male sperm. The fertilized egg now becomes the embryo which grows to be become the fetus, and then the child. Thus, life is greatly dependent on the female eggs.
The eggs are produced by the ovaries. The ovaries are thus called the primary female reproductive organs. Each ovary is a solid, ovoid structure about the size and shape of an almond, about 3.5 cm in length, 2 cm wide, and 1 cm thick. The ovaries are located in shallow depressions, called ovarian fossae, one on each side of the uterus or womb, on the side walls of the female pelvic cavity. They are held loosely in place by strong structures called ligaments.
How do the ovaries produce eggs?
The ovaries start development by the end of the third week of gestation in the female embryo which is shortly after fertilization, way before a woman misses her first period. By the fifth week which is just about the time of a missed period, the primordial germ cells or early sex cells also called oogonia appear in the ovary. It is these cells that will then undergo series of processes to form the female eggs.
Unlike the male, the female eggs or sex cells start development at this time (5th week of gestation) way before they are born. These primitive sex cells undergo some cell divisions and replication, and multiplication which results in the expansion of the oogonial population to approximately 6–7 million by the gestational week 20. These cells then begin to undergo a process called a programmed cell death or apoptosis. This will lead to a great decrease in their number as they begin to die off from this point. By the time a female child is born, she is born with about 1 million eggs, it may be up to 2 million in some cases. These eggs have undergone some level of maturation from the primitive oogonia and are called primary oocytes. Still in the womb, they undergo another special form of sex division called meiosis which will make them become mature sex cells. This process is however halted at a stage which will resume at puberty.
How many eggs does a female have?
A human female cannot produce new eggs as soon as she is born. Instead, her about 1-2 million eggs which are at a suspended growth phase wait for puberty to resume maturation and at the same time decline in number.
According to experts, a female loses a whooping average of about 11,000 eggs a month before they reach puberty. This continuous loss of eggs will continue as the woman ages. This is why a woman’s fertility declines with age. At the start of puberty, a female has an average of 300,000 to 500,000 viable eggs.
These eggs resume maturation at puberty, to be more accurate, at menarche. The beginning of menstruation and the menstrual cycle of a woman is preceded by ovulation, which is when the eggs fully matures and is released for fertilization by the sperm. From this point on, female loses about 1000 eggs monthly. This rate becomes accelerated after 35 years of age.
By the early 20s a female would have about 150,000 to 300,000 eggs. This will reduce to about 100,000 to 150,000 eggs in the early 30s, to about 27,000 eggs in the late 30s. This is one of the main reasons why pregnancy is more difficult and less likely at ages greater than 35 years.
Experts also approximate that by the time a person reaches age 37, they will only have about 20,000 eggs remaining. The approximate number of eggs lost to ovulation throughout a woman’s life time has been estimated to be about 450 eggs and the rest of the eggs degrade and die off with time.
By menopause, (50 to 51 years), the female has barely 1,000 eggs remaining. These eggs are mostly not viable or healthy and are almost nonfunctional. This is why technically, the egg count of a menopausal woman is zero and getting pregnant is near impossible without assisted reproduction. Menopause effectively marks the depletion of the ovarian reserve and the end of a females reproductive ability and menstrual cycle.
What happens to the female eggs after ovulation?
After the egg is released during ovulation, it moves into the fallopian tube. It stays there for about 24 hours, waiting for a single sperm to fertilize it. All this happens, on average, about 2 weeks before the next period. If no sperm is around to fertilize the egg, it moves through to the uterus and disintegrates. The hormone levels go back to normal, and the body sheds the thick lining of the uterus, and the period starts.
So if you are considering having a baby or your fertility, it is better to do so in your 20s when the eggs are at their peak and healthiest, if however, you are up to 35 years old and experiencing delay in conception, you can consult your gynecologist for the several assisted reproductive methods. Tests can also be performed to estimate your ovarian reserve and ascertain how heathy they are. The earlier this is done, the better chances of success.