Over the last several years, it appears that the incidence of infertility is increasing. This may be due to increased public awareness causing people to question their fertility and to seek help. Women are marrying at older ages and many are delaying childbirth until they establish their careers. Unfortunately, many don’t consider the “fertility implications” of waiting until their mid or late thirties to attempt pregnancy.
If society adhered to the biologic clock, pregnancy would be attempted in the teens and early twenties, during the most fertile time of a woman’s life. Obviously, this does not mesh with the societal clock as most women want to achieve more emotional maturity and develop the ability to properly support a child. It can be extremely frustrating and depressing to discover that having a much desired child will require fertility treatments.
The American Society for Reproductive Medicine (ASRM) defines infertility as the inability to conceive after one year of unprotected, regular, intercourse. The time is shortened to six months in women aged 35 and older.
It is clear that advancing female age is the “number one enemy” of female fertility. There is a direct correlation between age and fertility and fertility can decline very rapidly. This is one reason why a fertility specialist must be consulted early in the course of a couple’s infertility.
A female is born with a lifetimes supply on eggs within her ovaries. Each month an egg(s) is recruited and develops until maturity and is ovulated. The hypothalamus is the master gland that controls the processes of egg development and ovulation. It monitors the levels of various hormones and adjusts the output of others in a system termed the “hypothalamic-pituitary-adrenal axis”.
During the first days of the ovulatory cycle, the hypothalamus secretes gonadotropin releasing hormone (GnRH) which travels to the pituitary where it stimulates the production of follicle stimulating hormone (FSH). FSH directly stimulates the ovaries causing the recruitment of follicles (each of which containing an egg). As healthy follicles develop, they produce increasing amounts of estrogen. Estrogen travels to the hypothalamus where its levels are monitored and the production of FSH is adjusted accordingly.
Once the follicles mature, the hypothalamus releases GnRH which stimulates the pituitary to produce a surge of luteinizing hormone thus initiating ovulation. The leftover ovarian follicles begin to produce progesterone and are now termed the corpus luteum. Progesterone is needed to support development of the endometrium which will support the embedding embryo and resultant fetus.
Infertility results when any of these processes do not occur properly. Also, it is estimated that up to half of all couples will have a male component to their infertility. An evaluation of both partners is mandatory.
There are numerous processes that must occur for successful pregnancy to result. Most of the “diseases” that cause infertility are separated by the organ system affected.
- The male must produce enough sperm of acceptable quality to reach the egg and cause fertilization. Any deficiencies in quantity or quality lead to male infertility.
- The sperm must be ejaculated into the vagina where they swim in the cervical mucus through the cervix and into the uterus. Defects in cervical mucus, such as antisperm antibodies or poor consistency, can impede the sperms progress leading to infertility.
- The ovary must be capable of recruiting ovarian follicles that grow under the influence of FSH. The egg within the follicle must be genetically normal and have the ability to fertilize.
- Once the egg is ovulated (released) it must travel through the fallopian tubes to the distal (far) end which is where fertilization occurs.
- The egg and sperm “come together” and one sperm must penetrate the egg and cause fertilization. The resultant embryo must have a normal complement of chromosomes and be free of genetic defects.
- The uterus must be free of large obstructions such as polyps and fibroids. It must also be free of congenital defects, such as the bicornuate uterus (two horned uterus).
- The embryo must imbed into the endometrial lining and receive support and nourishment. The endometrium (lining) develops during the ovulatory cycle under the influence of estrogen and progesterone. Progesterone deficiency can lead to a “luteal phase defect” where the endometrium does not properly thicken.
- Once the embryo embeds and the fetus begins to develop the placenta begins to produce progesterone.
- The embryo must be free of genetic defects such as an abnormal number of chromosomes which can now be identified using PGD.