For pregnancy to occur naturally there must be:
- An adequate amount of healthy sperm
- Open fallopian tubes
- Healthy egg cells
- Normal uterus
The woman’s egg cells are the all important factor because while all the other elements can be ‘fixed’, the reproductive process, natural or assisted, has to start with the woman’s eggs as they are.
The menstrual cycle and
It's role in reproduction
The following happens in a natural menstrual cycle:
- Each month, the ovaries ‘produce’ approximately 10-20 egg-bearing follicles, out of which one follicle will become dominant and will ovulate the egg destined for ovulation during the cycle.
- These follicles come from the vast follicle pool that a woman is born with, but she will ovulate only about 300-400 eggs during her reproductive life.
- Starting at birth, the follicle pool is continually depleted by natural atresia, which is like a programmed degeneration in which the degenerated follicles are simply absorbed into the regular ovarian tissue.
- Likewise, the follicles recruited for possible ovulation each cycle will go into atresia.
- Follicle depletion by atresia explains why, as a woman ages, she will have progressively less follicles
left (this is called her ovarian reserve).
- The best follicles tend to be ovulated first because they respond best to the reproductive hormones. Therefore, increasing age not only means less follicles but also generally poorer quality follicles.
The ovulation process is regulated by two hormones produced in the pituitary gland of the brain.
- FSH (follicle-stimulating hormone) secreted after ovulation in the previous cycle recruits the follicles for possible ovulation in the next cycle.
- In the first half of the cycle, it will promote growth and development of the recruited follicles.
- The follicle that best utilizes FSH will become the dominant follicle and outgrow the rest.
- The egg destined for ovulation during the cycle will come from the dominant follicle.
- In response to FSH, the nutrient cells surrounding the egg will produce increasing amounts of
estradiol (E2), the dominant estrogen in non-pregnant women, causing both the follicle and the egg to grow.
- LH (luteinizing hormone) takes over follicle control towards midcycle because it causes the follicle and the egg it contains to mature before ovulation.
- In response to the increasing estrogen, LH secretion from the pituitary will surge. When it does, ovulation will occur in the next 24-36 hours. [It is this LH surge that is detected in home ovulation kits.]
- A mature follicle measures 18-20 mm, and the estradiol level corresponding to a mature egg is about 300 pg/ml.
Ovulation occurs when the follicle bursts open to release the egg, which, in normal women, is captured by the fingerlike opening of the fallopian tube.
- The egg will reside in the tube and will be fertilizable for at least 36 hours.
- When semen is deposited in the vagina at intercourse, the sperm cells travel through the cervix into the uterus. About 200 sperm cells will reach the fallopian tubes from the uterus.
- Fertilization occurs when one sperm cell penetrates the waiting egg.
After ovulation, the follicle that ovulated turns into a corpus luteum.
- In continuing response to LH, the primary function of the follicular cells this time is to produce progesterone, the hormone that maintains pregnancy if it occurs. They also continue to produce a small amount of estrogen.
- Progesterone and estrogen acting together cause the lining of the uterus (endometrium) to thicken
as it adds cell layers appropriate for the reception of an embryo if fertilization has occurred.
- A fertilized egg usually stays in the fallopian tube for 3-5 days by which time it will have become an embryo, and then it travels to the uterus where it will seek to implant itself in the uterine lining.
- If it successfully implants, then pregnancy occurs. The embryonic cells will attach to the lining and start interacting with the endometrial cells to form the placenta, which will be the lifeline carrying blood and nutrients to the embryo (and eventual fetus) from the mother.
- If no embryo is present or if an embryo fails to implant, then the uterine lining will start to break down about seven days after ovulation, and will be shed as menstrual blood in the next cycle. [Menstrual blood consists of endometrial cells, blood, and other endometrial secretions.]
- Progesterone levels will drop, and the hormonal levels of FSH, LH and estradiol will return to cycle baseline levels.
- Fourteen days after ovulation, if no pregnancy has occurred, the new menstrual cycle begins.
Basic facts about infertility
What is infertility and how common is it?
Infertility is the reduced capacity to conceive compared to general population.
- At least 6 million American couples (approximately 10% of reproductive-age population)
have difficulty conceiving.
- 25% of women will experience an episode of infertility during their reproductive life.
- 5-10% of normal fertile couples take more than 1-2 years to conceive.
Couples are encouraged to seek medical assistance for infertility if
- The wife is 35 or younger, but fails to conceive after 1 year of regular unprotected intercourse; or
- The wife is older than 35 and fails to conceive after 6 months of regular unprotected intercourse; or
- The patient has had more than 2 spontaneous abortions or stillbirths
What are the common causes of infertility?
- 10-15% Ovulation dysfunction
- 30-40% Pelvic factors (tubal, endometriosis, adhesions)
- 30-40% Male factor
- 15-20% Cervical factor (or abnormal sperm-mucus interaction)
- 10-15% Idiopathic or unexplained
It is not usually listed as a common cause for infertility, but it is increasingly a major infertility factor, as more women postpone motherhood in favor of career goals or higher education.
- A healthy fertilizable egg capable of developing into a healthy embryo is the most important factor for
- Because a woman is born with her lifetime supply of eggs, eggs age according to the woman’s chronological age, even if in her 30s, she manages to look 10-15 years younger.
- Nothing can be done – even theoretically – to slow down or stop egg aging, much less, reverse it.
- In some women, genetic factors cause premature ovarian failure, in which her fertilizable eggs are
depleted before she turns 40.
- Egg freezing allows a woman to beat the biological clock by banking her eggs when she is younger,
preferably under 30 but not older than 35.
- The female’s prime reproductive years are 18-25.
- After that, her fecundity (probability of being pregnant in a single menstrual cycle) declines considerably.
Age-related decline in fecundity
(compared to women aged 18-25):
- 25-29 - by 6%
- 30-34 - by 14%
- 35-39 - by 31%
- After 40 – Even with IVF, only 5% chance of pregnancy and live birth
In 50-60% of infertile couples, the cause is related to the male partner, either alone or with a coinciding female factor. That is why both partners are always evaluated in fertility care.
Male infertility may be due to:
Problems with sperm:
- No sperm or only immature sperm are produced
- Low sperm count
- Poor sperm movement and abnormal sperm shapes
- Blockage or absence of the sperm ducts (vas deferens) from the testicles
- Dilated vein in the scrotum (varicocele)
- Hormonal imbalance
Problems in delivering sperm:
- Erectile or ejaculation disorders
- Previous testicular or spine injuries
- Some health factors
Approximately 10-25% of all couples undergoing infertility treatment are diagnosed with unexplained infertility.
- This means that the causes of their infertility are subtle and cannot be explained using the tests available to fertility specialists.
- The prognosis for couples with unexplained infertility depends primarily upon the age of the couple.
- The success rate is 15-20% for unexplained infertility treated with fertility medications and intrauterine inseminations (IUI), which is similar to the 20% monthly fecundity of a normally fertile woman.
- The success rate with IVF treatment, when the woman is 35 or younger, may be 50-60%, which is
the prevailing pregnancy rate in most IVF programs.
- IVF often identifies the underlying problem to be related to egg quality and embryo implantation (a uterine problem).
What are the chances of conception if there are no obvious fertility problems?
- Woman is younger than 30
- Previous full-term pregnancy
- Trying less than 3 years
- Not underweight, overweight or obese
- Both partners don’t smoke
- Less than 2 cups of coffee daily
- No use of recreational drugs
- Woman is older than 35
- Never conceived before
- Trying more than 3 years
- More than 2 spontaneous abortions or stillbirths
- Underweight, overweight or obese
- One or both partners smoke
- More than 2 cups of coffee daily
- Regular or recent use of recreational drugs