5 Most Common Causes of Infertility

A woman's body prepares for pregnancy each month (it's really optimistic about her baby-making possibilities). The lining of her uterus, the endometrium, swells and thickens and gets all puffed up with red blood cells until one of her ovaries releases an egg.

If there's no sperm to fertilize the egg, the uterus sheds the lining (we call this a period) and her body gets ready to start the process of readying it for pregnancy again.

The uterus' specialized (endometrial) cells are responsible for the swelling and thickening of the lining, and they're very good at what they do.

It's a problem when uterine tissue ends up in the wrong place -- say, the lining of the pelvis, or the bowel -- because the cells keep doing their job. They grow and bleed, scarring and inflaming delicate places. They also cause incredibly painful periods, painful bowel movements, pain during and after sex -- and, often, infertility.

Researchers don't know how that tissue comes to be in the wrong place, but there is hope for women with endometriosis who want to get pregnant. Talk to your doctor about your options.

Size does matter, but not where you think -- it's sperm size that's important when it comes to fertility. There is, in fact, a standard of perfection when it comes to sperm: oval, paddle-shaped head with a long tail.

Eggs aren't in search of crooked tails or pinheads -- in fact, they're not searching at all. It's the best sperm that finds the egg, and the curly-tailed dude just isn't going to cut it. (It's OK if a large percentage of a man's sperm aren't in tip-top shape -- you just want some of them to be.)

Sperm size and shape is referred to as sperm morphology, and it's one of three factors analyzed in a semen analysis. The other two are sperm motility, or movement, and sperm count.

Sperm have to be willing to get a move on. That last distance to the egg can only be crossed with some serious tail wiggling. More than 40 percent of a man's sperm have to be active swimmers for a good chance at fertility.

As far as numbers, sperm count is pretty straightforward -- you want to have more than 39 million sperm in an ejaculation for a chance at procreation [source: Mayo Clinic]. (That is not a typo. Million.)

You need an egg to conceive a baby. In the usual process, an egg is produced from a follicle in the ovary and released into the fallopian tube. But in a woman with polycystic ovarian syndrome, or PCOS, this process is disrupted by a hormone imbalance. The eggs in the follicles of the ovary never mature -- they simply become cysts, and no egg at all is released.

PCOS causes the ovaries produce more androgens than usual. Androgens, such as testosterone, are known as the "male hormones," but that's a misnomer. Men and women both make them.

This "too much testosterone" condition doesn't just affect egg production -- it can also cause unwanted hair growth (in the form of a mustache, for example), smaller breasts, acne and thinning hair. Obesity is also a hallmark of PCOS, which is why the first advice a doctor often gives to a woman with PCOS hoping to get pregnant is to lose weight and make other lifestyle changes. As far as drugs and procedures go, the best treatment researchers have found so far is clomiphene, a drug that stimulates ovulation.

Varicoceles might look a little alarming, but they're common -- 40 percent of men struggling with infertility have them [source: WebMD]. Put simply, they're varicose veins in the scrotum. Put a little more scientifically, it's when the veins in the spermatic cord responsible for getting blood to the testicles are backed up. Doctors and nurses refer to the look and feel of a varicocele as "a bag of worms." Just what you want your scrotum to be described as!

Not all varicoceles need to be fixed -- just if they're painful or messing up your sperm production. The solution? Surgery or a procedure called varicocele embolization, which is becoming more popular because, unlike surgery, it doesn't require general anesthesia or cutting into the scrotum (four words that should never be typed together).

One of the many reasons it's so important to get tested for STDs is that some have no symptoms but can make you infertile. Chlamydia and gonorrhea, for example, which are very common, can lead to pelvic inflammatory disease (PID).

PID even sounds painful -- your pelvis should never be described as "inflamed." But when bacteria manage to make it past your cervix and crawl right up into your reproductive organs, that's what happens.

These bacteria can scar the fallopian tubes, making it impossible (or nearly so) for egg and sperm to meet. Even more dangerous, an egg can get fertilized and then completely stuck in the fallopian tube instead of making it to the uterus. The uterus expands to accommodate a growing fetus -- the fallopian tubes simply are not made to do the same and can rupture. This misplaced pregnancy is called an ectopic pregnancy, and it can kill a woman.

The best way to treat PID is as it's happening, and with antibiotics. Unfortunately, once damage is done, it's done, and it can't be fixed.

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