I was lucky. I had six easy pregnancies and six natural births. Four girls and two boys. Some women, however, aren't so lucky. The embryo starts to grow outside the womb. This is called ectopic pregnancy.

How does this happen? The first part of the cycle is natural enough - eggs from ovaries to womb through the Fallopian tubes. Along the way, they meet the sperm and are fertilized. Englishbin.com tells the rest:

The fertilised egg continues on to the womb, where it implants itself to the wall and continues to grow.

However, sometimes the embryo implants itself outside the womb, most often in the fallopian tubes themselves, and this is known as an ectopic pregnancy.

BitchPhd Blog has these startling figures:

In the U.S., about 300 women a year die from pregnancy. More than one in five pregnant women who is admitted to a hospital goes there not to deliver, but because of some pregnancy-related complication. Ectopic pregnancies *alone* constitute a little over 1.5% of all pregnancies in the U.S.; for women of color, for some reason, the rate of ectopic pregnancy--which is always fatal if not terminated--is 2%.

Medline Plus suggests these methods of prevention:

Most forms of ectopic pregnancy that occur outside the fallopian tubes are probably not preventable. However, a tubal pregnancy (the most common type of ectopic pregnancy) may be prevented in some cases by avoiding conditions that might scar the fallopian tubes. The following may reduce the risk of a tubal pregnancy:

• Avoiding risk factors for pelvic inflammatory disease (PID), such as multiple sexual partners, intercourse without a condom, and sexually transmitted diseases (STDs)
  


• Early diagnosis and treatment of STDs
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• arly diagnosis and treatment of salpingitis and PID