Conception is the all-encompassing term given to the general act of becoming pregnant. For most soon to be parents, conception refers to the moment that they create the miracle of life.
How does conception happen?
Conception occurs after sex, when the sperm from a man’s ejaculate and the ovum from a woman’s ovary merge together to form a viable zygote, or fertilized egg, which then implants in the uterus as an embryo and grows over 9 months to become a baby. Conception can also be assisted in the processes known as intrauterine insemination (IUI), in-vitro fertilization (IVF) and intracytoplasmic sperm injection (ISI).
What is sperm, and where does it come from?
Sperm, or spermatozoa, is the male gamete, or male reproductive cell that carries the genetic information that will, along with the female gamete, make up the complete set of chromosomes that develops into an embryo. Besides the obvious importance of a sperm cell, they also carry one more huge responsibility in the conception process – whether the sperm possesses the chromosome X or Y determines the gender of the baby.
A man’s body produces billions of billions of sperm cells in his life. The number is astronomical. It takes on average 2-3 months for a sperm cell to mature to the point of being released through ejaculation, along with around 300 million others in each output of such. Sperm cells are the product of the typically male hormone Testosterone. Production of sperm originates in the two glands in the scrotal sac beneath the penis. Sperm thrive in temperatures of 34 degrees Celsius, around four degrees cooler than the average body temperature, which is why they are stored in the testicles which hang outside the body. The sperm, once created, is stored within a 6 metre long, coiled tube until just before ejaculation, where it is scooped up and mixed with semen.
What is an ovum, and where does it come from?
An ovum, or egg, is the female gamete, or female reproductive cell that carries the genetic information that will, along with the male gamete, make up the complete set of chromosomes that develops into an embryo.
The ovum, or egg, is formed inside the ovaries of a woman on a regular cycle, and released regularly in the process known as ovulation. Women are born with the building blocks to all the eggs they will ever produce, these are commonly known as ‘fertility opportunities’, and normally number in enough for on average around 1-2 million. During a woman’s life she will lose around one half to three quarters of these fertility opportunities before she even reaches puberty and starts to menstruate, in a process known at atresia. With each cycle of ovulation a woman uses approximately 1000 fertility opportunities, even though only one mature ovum is produced.
During ovulation, the mature ovum is released from the ovary into the fallopian tube, where it may be fertilized by the sperm and implanted into the womb. If the egg remains unfertilized it will slowly stop producing hormones, which causes the lining of the uterus begins to break down and exit the body in the process of menstruation.
How does the sperm fertilize the ovum?
Before the sperm makes it to the ovum, there has already been a flurry of activity leading to the act of it penetrating the egg. Even though millions upon millions of sperm are released in each ejaculation, only one single sperm cell is required to fertilize each egg.
Once those millions of sperm make it through the cervix, whether aided or hindered by the cervical mucus, they still have a long way to go. The path from cervix to fallopian tubes via way of the uterus is about 18cm, and can be traversed in as little as 45 minutes by a fast swimming cell. The trip can also take significantly longer, up to 12 hours. Once in the fallopian tubes the sperm can survive for up to 7 days waiting to find an egg, hence why you can still fall pregnant even if you don’t have sex at the exact moment of ovulation.
But majority of sperm cells that even make it to the fallopian tubes don’t survive long. Half head towards the wrong fallopian tube and become lost and trapped, or die along the long, perilous journey towards the egg. On average, of the quarter of a billion sperm released in ejaculation, only a few dozen will make it to the outer shell of the ovum, where the real race begins. Only one singular sperm can penetrate the outer shell of the egg to combine genetic material and become a zygote, and once that lucky cell is inside, the door is instantaneously closed to all others. After all that work they still don’t make it.
What happens if more than one sperm fertilizes the egg?
It is extremely rare that more than one sperm is able to penetrate an egg, and if it does occur, the egg cannot mature into a fetus. The abundance of genetic information in the ovum will cause it to deteriorate and die.
There have been recent studies that are researching more into the possibilities of multiple sperm fertilization of one egg, but so far there have been no definitive conclusions as to whether it is possible for an ovum that has been penetrated by more than one sperm to survive.
What happens if the more than one sperm fertilizes more than one egg?
It is possible for a female to release more than one mature egg during ovulation, which can then in turn be fertilized by different sperm. This results in multiple fertilized eggs becoming viable zygotes in what is known as ‘fraternal multiple birth’ (non-identical). You can find more information on multiple pregnancy and birth in our pregnancy section.
What happens to cause identical multiple births?
Identical multiple birth occurs when one sperm cell penetrates and fertilizes one egg, which then splits into more than one zygote but carries the same genetic material. You can find more information on multiple pregnancy and birth in our pregnancy section.
What happens after fertilization?
After the egg is fertilized, it closes its doors to all other sperm and the process of forming a unique genetic composition starts immediately. The new cell that the two individual clusters of chromosomes have created begins rapidly dividing and is now known as a blastocyst. It travels back down the fallopian tube, in a journey that takes about 3 days, to the uterus, where it will attach itself to the wall and develop into an embryo and a placenta. It is at this time when you are considered ‘pregnant’.