Ectopic pregnancies are most often caused by conditions that block or slow the passage of a fertilized egg (embryo) through the fallopian tube to the uterus.

Although an ectopic pregnancy can occur in any woman who is fertile and sexually active, women with pre-existing fallopian tube damage are more likely to develop the condition. In fact, most cases of ectopic pregnancy are the result of scarring caused by tubal infection or surgery involving the fallopian tubes. In some cases, women are born with tubal abnormalities.

Common causes of fallopian tube abnormalities include:

• Sexually transmitted diseases (e.g., chlamydia, gonorrhea)
  
  
• Endometriosis
  
  
• Pelvic inflammatory disease (PID), especially salpingitis
  
  
• Previous pelvic surgery, especially procedures involving the fallopian tubes (e.g., tubal ligation, tubal reversal)
  
  
• Diethylstilbestrol (DES) exposure
  
  
• Appendicitis or ruptured appendix

Other risk factors for ectopic pregnancy include:

• Previous ectopic pregnancy. Women who have had one ectopic pregnancy are more likely to experience another one. This is due to the underlying cause of the initial ectopic pregnancy, combined with the scarring caused by the first episode’s treatment.
  
  
• Fertility drugs. Women who conceive as the result of fertility drugs have a slightly higher risk of developing an ectopic pregnancy.
  
  
• In vitro fertilization (IVF). Women who conceive as the result of IVF have a slightly higher risk of developing an ectopic pregnancy.
  
  
• Morning after pill. According to the National Institutes of Health (NIH), when the morning after pill fails to prevent a pregnancy, the pregnancy is 10 times more likely to be ectopic.
  
  
• Progestin-only birth control pills (“mini pill”). The NIH estimates that women who become pregnant while taking the mini pill are five times as likely to have an ectopic pregnancy.
  
  
• Intrauterine device (IUD). Women who become pregnant despite using an IUD as a form of contraception are more likely to develop an ectopic pregnancy. According to the NIH, the risk while using a copper-bearing IUD is 5 percent higher, whereas the risk while using a progestin-releasing IUD is 15 percent higher. This occurs because the mobility is affected by the contraception device and the transport is slower.
  
  
• Age. A woman’s risk of ectopic pregnancy increases with age.
  
  
• Numerous pregnancies. Women who have had three or more pregnancies are more likely to develop the condition.
  
  
• Race. Black and Hispanic women are more likely to have an ectopic pregnancy than white women. 
  
  
• Smoking. According to the Centers for Disease Control and Prevention (CDC), tobacco use may slightly increase a woman’s risk of ectopic pregnancy.