For many people struggling with infertility, it can come as some relief to learn the degree of complexity of human reproduction. Conception requires several physical systems – especially the endocrine and reproductive functions – to be in sync.
Unfortunately, just one variation can disrupt an intricate series of events necessary for conception. The result is that there can be dozens of causes of infertility. Infertility can result from problems with:
- The makeup of individual cells (oocyte, or egg, from the woman and/or sperm from the man)
- The journey that each of the cells needs to make from their points of production to their meeting
- The condition of the uterus, where fertilized cells’ will implant and grow
Egg cells and sperm
To better understand the production of egg cells by the female body, read more about ovulation. Similarly, to better understand the production of sperm by the male body, read more about sperm motility and morphology.
For now, though, let’s focus on what happens after sperm and eggs are produced individually, when their respective journeys become important to fertility and can cause infertility. After ovulation, the egg cell must:
- Be collected by fimbria (tiny waving extensions at fallopian tubes’ ends) into a fallopian tube, and
- Be propelled by cilia (hair-like cells) through the tube toward the uterus.
And after sperm are made in thread-like seminiferous tubes within the testicle, they must:
- Be sent to the epididymis (more coiled tubes) to continue maturing, until:
- They are combined with fluid from the prostate gland in the seminal vesicle (a storage area) on their way to
- Ejaculation through the prostatic urethra, the penis’ interior tube.
Conditions for conception
Problems with any of these organs or processes can prevent the egg and sperm from meeting, resulting in infertility problems. For a man to impregnate a woman without medical assistance, the following conditions are optimal:
- A high number of sperm (count and volume)
- Of the right shape (morphology) and
- Ability to move (motility) and
- Seminal fluid quality to transport sperm cells
- Penile erection and ejaculation must deliver semen into the vagina.
Female conditions for pregnancy
For a woman to get pregnant, the following conditions are optimal:
- A high quality egg cell
- Expelling of the egg cell from the ovary
- A fallopian tube that is able to move over to the ovary and pick up the egg cell and transport it through the fallopian tubes in a timely manner, that is, in sync with the preparation of her uterine lining
- Cervical and vaginal fluid that is sperm-friendly – liquid enough for sperm to swim through, and with the right chemical composition for sperm to survive
- Adequately proliferated (plumped up, if you will) uterine lining to receive the fertilized egg
Most conceptions occur within the fallopian tube. After the fertilized egg becomes an embryo and grows to the blastocyst stage in the first few days, the embryo should move from the fallopian tube into the uterus.
If there are no structural problems with the woman’s uterus and her hormones have adequately signaled the uterine lining to develop properly, the embryo should implant within the uterus. If fertilization has not occurred, the woman will have a menstrual period and shed the uterine lining. With so many factors involved, it is easier to understand some of the causes of infertility.