Ectopic pregnancy usually occurs in women with fallopian tube dysfunction. There are a number of risk factors for ectopic pregnancies, among them pelvic inflammatory disease, infertility, DES exposure, tubal surgery, smoking, previous ectopic pregnancy, multiple sexual partners, current IUD use, tubal ligation, and previous abortion. The most potent risk factor in the development of ectopic pregnancy is tubal surgery.

• Risk factors in the development of ectopic pregnancies may be occupational, environmental, genetic, and viral. The following table summarizes these risks and its odds ratio:

• Tubal surgery. It is known as the major risk factor for ectopic pregnancy developemnt.^[1][2]
• Tubal ligation. Although tubal ligation is highly effective in preventing pregnancies, if a pregnancy does occur, it is more likely to be ectopic.^[3]
• Previous ectopic pregnancy. Same as having a previous ectopic pregnancy increases the risk for further ectopic pregnancies, having a intrauterine pregnancy decreases this risk.[4][./Ectopic_pregnancy_risk_factors#cite_note-pmid8641479-1 [4]]^[5][6]
• In-utero DES exposure. The usage causes a loss of fimbriae and stenosis of fallopian tubes, which may increase up to 3 times the risk of ectopic pregnancy as compared to unexposed women.^[7]
• IUD. It is thought that IUD-induced inflammation may result in deciliation of the endosalpinx and then delays ovum transport, altough, the exact mechanism is not fully understood.^[4]
• Documented tubal pathology. Ectopic tubal pregnancy may occur in a blocked tube with contralateral tubal patency, although, this association was found to be weaker for those with two blocked tubes.^[8][9]

• Infertility. Treatment of infertility, such as in vitro fertilization is associated with a 2 – 3 % increased risk compared with the general population.^[10][11][12]
• Previous STD. This possibly due to tubal scarring from gonococcal and chlamydial infections, which produce changes in tubal function leading to delay in ovum transport and tubal implantation.^[4][7]
• Multiple sexual partners. There has been an association between multiple sexual partners and ectopic pregnancies, especially when 1st intercourse < 18 years old.^[7]
• Prior pelvic / abdominal surgery. Women with histories of laparotomy and appendectomy have higher risk of developing an ectopic pregnancy, although this risks increases even higher when it involves tubal involvement.^[13]
• Cigarette smoking. Inhalation of cigarette smoke may impair fallopian tube function by affecting on ciliary beat frequency and smooth muscle contraction.^[14][15]
• Pior abortions. There is conflict between studies in revealing an association; the cause of this relationship is most likely due to infection, hormonal imbalance, or immunologic factors.^[16][17]
• Advanced age. There is a 9 times-fold increased risk of developing an ectopic pregnancy in women ≥39 as compared with those ≤26 years.^[18][4]
• Vaginal douching. It is thought by some to increase ectopic pregnancies.