How Normal Reproduction Works

Sometimes it seems incredible to me that any humans ever conceive given the complexity of reproduction and the multitude of factors that can prevent conception. As fertility physicians we always need to keep in mind how the normal system works in order to evaluate for problems and suggest therapeutic interventions. Personally, I have always felt very privileged to work with patients seeking fertility. The rewards are great but the emotional costs can be high for both patient and caregiver. The news is sometimes not good and the treatments can be expensive and invasive. Unfortunately, the more expensive and invasive treatments work better than the less expensive ones. Sometimes, this point is hard to get across.

DrG: I am sorry that the IUI didn’t work. But remember that I thought the chance of pregnancy was only about 5% per attempt.

Patient: So why didn’t it work.

DrG: Well, it only works 5% of the time and this month you were in the bad 95%.

Patient: But why didn’t it work for me this time.

DrG: Because most of the time it unfortunately doesn’t work given your situation.

Patient: But I want it to work.

DrG: I understand but unfortunately this is not a very successful option. IVF works better.


Patient: But I don’t want to do IVF.


DrG: Well then we can stick with this option but it only works 5% of the time.

Patient: But I want something that works better.


DrG: IVF would work better.


Patient: But I don’t want IVF.

DrG: Then we are unfortunately a bit limited by the situation given your particular case.

Patient: But I want to get pregnant.

DrG: Then we should consider additional IUI cycles or move to something more intensive…


Patient: But I don’t want to do additional IUIs and I don’t want something more invasive.


DrG:


I am not unsympathetic to patients who are stuck between a rock and a hard place, but there are always trade offs in life. For example, you could read this blog every day until I work though all of the questions or you could go to Amazon.com and preorder the forthcoming "100 Questions about Infertility." If you do the latter then I will have 37 cents more to spend the next time I go to the Safeway down the street. If you are the former, then print out this post and start making your scrapbook:

1. How does normal human reproduction work?

Norman human female reproduction depends on the correct functioning of four components of a woman’s body: the brain, the ovary, the fallopian tube, and the uterus. At the time of her birth, a woman’s ovary contains all of the eggs that she will ever have. These eggs are contained within fluid-filled sacs called follicles. Every month, the brain sends out a signal from the pituitary gland (a gland located at the base of the brain) stimulating the follicles to grow. Not surprisingly, this hormone is called follicle-stimulating hormone (FSH).

Under the influence of FSH, a group of follicles begins to grow, but by the fifth day of the reproductive cycle a single dominant follicle has already been selected. This dominant follicle may be either on the right ovary or the left ovary. As it grows, the follicle produces an important steroid hormone called estrogen. Estrogen causes the lining of the uterus (endometrium) to thicken in anticipation of the eventual implantation of an embryo. By mid-cycle, this follicle has grown to a diameter of 20 to 22 mm. At this time the brain releases a second hormone, called luteinizing hormone (LH), from the pituitary gland. LH is the trigger that induces ovulation. Approximately 36 hours after the LH surge, the follicle releases the egg.

It is the job of the fallopian tube to trap the egg. If the fallopian tube fails to catch the egg, then pregnancy cannot occur. During intercourse, tens of millions of sperm are deposited in the woman’s vagina when her male partner reaches orgasm and ejaculates. While the egg is safely held within the fallopian tube, these sperm may swim from the vagina, into the cervix, through the uterus, and up into the fallopian tube, where fertilization can occur.

Normally, a fertilized egg travels through the fallopian tube for 5 days after fertilization, at which point it reaches the uterus. (A fertilized egg that remains trapped within the fallopian tube is called a tubal pregnancy or ectopic pregnancy, and can be a life-threatening condition.) It divides many times along the way. By the time it reaches the uterus, it has grown to hundreds of cells and is called a blastocyst.

Once the egg is released from the ovary, the follicle (now called a corpus luteum) produces both estrogen and a new hormone: progesterone. Progesterone changes the estrogen- primed endometrium, allowing implantation of the embryo and thus permitting pregnancy to occur. If a pregnancy does not arise, then 2 weeks after ovulation, the levels of estrogen and progesterone both fall and a menstrual period ensues, in which the woman’s body sheds the lining of the uterus. Menstrual flow lasts approximately 3 to 5 days in most women. Overall, human beings are not very fertile, with maximum pregnancy rates of only 20% to 25% per cycle during the years of peak fertility (the second and third decades of life).