July 26, 2014
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Fertility


Fertility 101

Reproduction can be a complex process. Therefore, it's important to understand how the process works. Learn more about the male and female reproductive system, why timing is everything, and how age can affect your fertility.

FERTILITY BASICS

The biology of fertility is complex - for both men and women. In order to conceive, each partner's reproductive system must function correctly.

It's probably been a while since biology class, so it can't hurt to refresh your memory with some basics. To help you, we've provided short primers on female biology and male biology.

Female biology

A woman is born with all the eggs she'll ever have.
A woman is born with over a million eggs in her ovaries. By the time she reaches puberty, she'll have about 300,000 left. Of these eggs, only about 300 will mature and be released during her reproductive years.

All of her eggs are stored in her ovaries. The hormones she needs for menstruation and to become pregnant are produced by her hypothalamus, pituitary, and ovaries.

Anatomy of the female reproductive system

Figure 1: Anatomy of the female reproductive system

It's all about the cycle.
A woman's monthly menstrual cycle drives her ability to conceive. The cycle begins on the first day of a woman's period and typically lasts about 28 days. The first day begins not when she is spotting, but when she experiences regular flow.

The cycle is then divided, by ovulation, into two phases:

Follicular phase: days 1-14
During the first 13 days of a typical female's cycle, a hormone called the follicle stimulating hormone (FSH) is released from the pituitary gland and stimulates the development of a fluid-filled sac called a follicle in one of the ovaries. This follicle then produces a single mature egg. While this is happening, the follicle secretes estrogen, which prepares the cervical mucus at the entrance of the uterus to receive sperm. The endometrium (lining of the uterus) also begins to thicken during this phase.

A surge in luteinizing hormone (LH), also produced by the pituitary gland, facilitates the final step of the maturation of the egg and, on about the 14th day, triggers ovulation. The egg is released from one of the ovaries and travels down a fallopian tube. When a couple has intercourse, a man's sperm attempts to swim past the cervical mucus and into the fallopian tube, where it can fertilize the egg. The optimal days for conception are the ones just before and after ovulation, generally days 11-17.

Luteal phase: days 15-28
Following ovulation, the hormones progesterone and estrogen develop and maintain the endometrium (lining of the uterus) for receiving a fertilized egg. If the egg is fertilized, the embryo travels down the fallopian tube to implant itself into the endometrium on about the 20th day of the cycle. Here it will develop into a fetus. If the egg is not fertilized, it still continues its journey into the uterus, but the uterus does not receive the hormonal message that fertilization has occurred. Without this hormonal message, the uterus ends its preparations for pregnancy, discarding the endometrial lining, as well as the extra blood and nutrients it has built up. This familiar event is known by a number of names: menstruation, menstrual bleeding, period, and many others.

The luteal phase is typically 14 days. It is important to realize that not all women have 28-day cycles. Therefore, the specific days of your follicular and luteal phases may be different. For more information, speak to your health care provider.

The critical role that hormones play
If this sounds complex, that's because it is. Each step in the cycle is controlled by hormones that must generally be produced in the correct amounts, at the right times, in order for a woman to conceive. The key hormones that affect this cycle are follicle stimulating hormone (FSH), luteinizing hormone (LH), progesterone, and estrogen. Any interruptions can disrupt a couple's ability to conceive. Many factors may play a role in reducing fertility such as age and lifestyle choices.

The menstrual cycle and the role of hormones

Figure 2: The menstrual cycle and the role of
hormones

LH - luteinizing hormone
FSH - follicle stimulating hormone
Enlarge diagram
Image © Dr. J. Herrero Garcia

Embryo development and implantation

Figure 3: Embryo development and implantation

Enlarge diagram
Image © Dr. J. Herrero Garcia

Anatomy of the male reproductive system

Figure 4: Anatomy of the male reproductive
system

Enlarge diagram
Image © Dr. J. Herrero Garcia

Male biology

The importance of sperm
For men, an essential part of fertility involves the creation of normal, mature sperm.

Producing sperm is a multi-step process. Sperm production begins in a man's testes and passes through the epididymis, which stores and nourishes the sperm. The sperm then travel through the vas deferens and are stored in the seminal vesicles.

When a man ejaculates, the sperm mix with fluid to create semen. If the sperm are healthy and able to travel through a woman's cervix and uterus and into her fallopian tubes, one of them may fertilize the egg.

A man will continue to produce sperm, no matter what his age. However, age can negatively affect male fertility. Find out more about how age affects fertility.

The critical role that hormones play
A man's reproductive system depends on hormones that stimulate and regulate the production of sperm. You may be surprised to learn that many of the same hormones that control a woman's reproductive cycle also control a man's reproductive system:

  • follicle stimulating hormone (FSH) stimulates sperm production
  • luteinizing hormone (LH) stimulates the production of testosterone

In both men and women, testosterone plays a key role in health and well-being as well as in sexual functioning. For example, testosterone can enhance libido (sexual drive), increase energy, and protect against osteoporosis.

Finding that delicate balance
Creating sperm is a complicated process. The body must generate hormones at the right time, in the proper amounts, in order for healthy sperm production to occur. Any disruption in this process can make it difficult to conceive. In addition, age and certain lifestyle choices may also affect sperm production. For example, smoking and excessive use of alcohol have been shown to have a negative effect on a man's fertility.

And by the way...

The male partner is just as likely to be the source of infertility as the female partner. The cause is attributable to male factors approximately a third of the time, to female factors a third of the time, and for the remainder, infertility is caused by a combination of problems in both partners, or is unexplained.

If you're concerned about infertility issues, you may wish to see a health care provider or visit a fertility clinic.

Reference: Fertility LifeLines

TIMING INTERCOURSE TO GET PREGNANT

When it comes to fertility, timing can be everything. Most people know that a woman is able to conceive for a short time each month. The question is: when and for how long?

Timing intercourse

Fertility experts generally recommend that you have sexual intercourse at least every other day just before and after you ovulate.

During ovulation, the egg that has matured in your ovary is released and settles into one of your fallopian tubes. After ovulation, this egg will survive for only about 24 hours. A man's sperm, however, can live for 48 to 72 hours in a woman's reproductive tract.

Assuming that a woman has a 28-day cycle and that ovulation occurs around the 14th day, her most fertile times occur between days 11 and 17 of her cycle. But before you apply this math, take into consideration that not all women have 28-day cycles. The key to timing your intercourse is knowing the length of your cycle so you can estimate when ovulation occurs. It's also important to understand that this "fertile window" can be highly unpredictable, even if your menstrual cycle is usually regular.

Predicting ovulation

Pinpointing the precise day when ovulation should occur is a bit of a challenge.

Menstrual cycle chart

The easiest, but least precise, way to predict this is to chart your menstrual cycle on a calendar. Remember, your cycle begins on the first day of your period. This is the day when you experience regular flow (and not just spotting). Get a refresher on the natural monthly cycle, or try our simple ovulation calculator.

Track the intervals between your periods to get a better understanding of how long your cycles are. Once you know how many days your cycle generally is, subtract 14 days from the predicted end of the cycle to determine time of ovulation.

Basal body temperature (BBT) chart

Another option may be to use a BBT chart. To measure BBT, the female partner simply takes her temperature every morning when she wakes up and charts it on a calendar. Your BBT should rise about a half degree two days after a surge in the luteinizing hormone (LH) occurs, indicating that ovulation has happened. Physical release of the ovum (egg) probably occurs on the day before the first temperature elevation.

Here is an example of what normal and abnormal BBT charts would look like:

Normal basal body temperature (BBT) chart

Normal basal body temperature (BBT) chart
Abnormal basal body temperature (BBT) chart

Abnormal basal body temperature (BBT) chart

If you are tracking your BBT and find that your chart looks more like the abnormal BBT example rather than normal one, this could be a sign that your hormone levels are unusual or there could be a problem with your ovulation cycle. You may want to talk to your doctor or a fertility specialist. Find a fertility clinic near you.

Ovulation predictor kit

You can also buy an ovulation predictor kit at your local pharmacy. They're available without a prescription, are simple to use, and can usually predict ovulation 24 to 36 hours in advance. The kit works by measuring increases in a woman's LH level just prior to ovulation.

Unfortunately, these methods are not perfect. For more information, talk to your health care provider or a fertility specialist .

Looking for definitions for fertility terms? Visit our Fertility Glossary.

Reference: Fertility LifeLines

AGE AND FERTILITY

It's a fact of nature. There's no way around it. Age affects your ability to conceive - for both men and women. Age also affects when you need to seek help (use the clinic locator to find a fertility clinic near you) for your fertility:

  • women under 35 who are unable to conceive after a year of regular, unprotected intercourse
  • women aged 35 to 37 who are unable to conceive after 6 months of regular, unprotected intercourse
  • women over 37 (women over 37 do not need to wait 6 months before seeing a doctor, because waiting too long to seek help could harm their chances of conceiving).

Age does affect a woman's fertility

Age is not an absolute barrier to conception, but as a woman gets older it does become more difficult for her to conceive. The truth is that a woman's fertility naturally starts to decline in her late 20s. By age 35, a woman's fertility is reduced by nearly half. The reason is straightforward. A woman is born with all the eggs she'll have. And with time, the supply diminishes. The remaining eggs also age along with the rest of the body.

Maternal age and fertility

There are other age factors. A woman's hormone levels change with age and can, in some cases, cause irregular ovulation. This is all normal. If you're older, especially over the age of 40, it may be more difficult to conceive.

Finally, some studies suggest that miscarriage rates increase with age. Both maternal and paternal age can play a role.

Though age shouldn't stop you from trying to conceive, it is probably a good idea not to wait too long to begin planning your pregnancy. There are also ways to manage your ability to conceive as you age. However, you should factor into the equation the amount of time it takes just to get a referral to a fertility specialist. The testing and diagnostic processes can also take a long time and the treatment process may take more than one cycle. Learn more about fertility treatment options.

If you have concerns or questions about your ability to conceive, talk to your doctor or a reproductive specialist. Use the fertility clinic locator to find a fertility clinic near you.

You should also see a doctor if you are under 35 and have been trying to conceive for at least 12 months, or if you are 35 to 37 and have been trying to conceive for at least 6 months. Women over 37 do not need to wait 6 months before seeing a doctor, because waiting too long to seek help could harm their chances of conceiving.

Age affects men too...

Age affects male fertility as well. As a man gets older, his testosterone level naturally declines and, in turn, his sexual drive may wane. The quality of a man's sperm also drops as he gets older. Despite this, he will continue to produce sperm no matter what his age is.

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