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Ectopic Pregnancy

What Causes Ectopic Pregnancy?

Thursday, March 22, 2012 - 11:20

Contributing Author: Guy Slowik FRCS

It's important to remember that in most cases of ectopic pregnancy, the cause is unknown. However, several factors can raise your risk for an ectopic pregnancy:

Fallopian Tube Problems

The fallopian tubes are five- to six-inches long and have funnel-shaped endings. They are designed to pick up the egg from the ovary and transport it to the womb. The embryo is transported through the tube by a combination of the contractions of the muscles surrounding the tube and the movement of fine, hair-like cells lining the tube. After fertilization occurs inside the tube, these "squeeze and sweep" the embryo out of the fallopian tube and into the uterus.

A damaged fallopian tube can block this motion and keep the embryo from reaching the womb. The most common causes of tubal damage are:

  • Previous pelvic infection. The infections most likely to cause fallopian tube problems are sexually transmitted diseases (STDs), such as gonorrhea and chlamydia. These STDs can be especially dangerous for women, because they may not cause any symptoms until the disease has traveled into the abdominal cavity and infected the reproductive organs. This can lead to serous condition called pelvic inflammatory disease, or PID. Mild pelvic infections can destroy the delicate hair-like cells lining the fallopian tubes. Severe infections can scar the tubes, causing them to become blocked. Women who have had pelvic infections have a five times greater risk of ectopic pregnancy.
  • Use of an intrauterine contraceptive device (IUD). IUD's can place a woman at an increased risk of pelvic infection, scarring of the fallopian tubes, and ectopic pregnancy.
  • Endometriosis is a medical condition that causes uterine tissue to grow outside the womb and attach itself to internal organs. It can cause damage and scarring to the fallopian tubes, raising the risk of ectopic pregnancy.

For more detailed information about endometriosis, go to Endometriosis.

Nice to Know: What Is PID?

Pelvic inflammatory disease (PID) is an infection of the female reproductive organs. PID is usually caused when sexually transmitted bacteria, such as those that cause chlamydia or gonorrhea, migrate from the vagina into the uterus and upper genital tract. Using an intrauterine device (IUD) or having gynecologic procedures such as an abortion may also introduce bacteria that could cause PID.

Sometimes a woman may have PID and not know it (many times a girl gets it as a teenager). It may be found only later when she has trouble getting pregnant and a doctor discovers that her reproductive organs have been damaged, or when she experiences pelvic pain later in life. PID can cause scarring on the fallopian tubes, a prime risk factor for an ectopic pregnancy

About one million American women receive a diagnosis of PID each year. More than 100,000 women become infertile as a result of PID and thousands suffer complications of pregnancy, such as ectopic pregnancy. The best way to prevent PID is to use a barrier method of birth control, such as condoms, that helps prevent STDs.

Symptoms of PID include abdominal pain, irregular periods, abnormal vaginal discharge, and pain during urination and intercourse. However, many women experience no symptoms. If you have had unprotected sex with multiple partners, get tested regularly for STDs and have regular gynecological checkups. PID can be cured with antibiotics, but left untreated it can cause infertility and even be life-threatening.


Smoking is also associated with up to a five times greater risk of ectopic pregnancy. This may be due to the nicotine in cigarettes. Nicotine stimulates contractions in the fallopian tubes. This can cause "spasm," resulting in temporary blockage of the tube so the embryo cannot pass through.


Previous abdominal surgery, particularly surgery involving the reproduction system increases the chance of having an ectopic pregnancy. In particular, when pregnancy occurs after an unsuccessful tubal sterilization, there is a 50/50 chance that it will be ectopic. In addition, if a woman has her tubal ligation (a procedure in which the fallopian tube is surgically severed in order to prevent pregnancy) reversed, she is at a high risk for ectopic pregnancy. This is because the tube may be narrowed at the spot where it was rejoined. Because of the high risk of ectopic pregnancy, if you become pregnant after surgery to your fallopian tubes, you should be seen by a doctor immediately.


Several hormonal medications have also been associated with ectopic pregnancies. These include:

  • Fertility drugs such as clomiphene citrate and pergonal
  • Contraceptive hormonal medications that contain progesterone-like hormones

Each of these hormonal medications may predispose women to tubal pregnancies by altering the ability of the fallopian tube to contract and squeeze the embryo through to the womb. If you conceive while on one of these medications, get evaluated by a doctor right away.

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