What Causes an Ectopic Pregnancy?

By Dr. Ananya Mandal, MDReviewed by Sally Robertson, B.Sc.

Normal implantation process

Every month, females of reproductive age release an egg or ovum from one of their ovaries during the menstrual cycle. This egg travels from the ovary towards the womb via the fallopian tube, where it may or may not be fertilized by sperm.

The fallopian tubes are around 4 inches long and are lined with hair-like structures on the inside called cilia. These cilia move to push the fertilised egg along the fallopian tube in the direction of the womb where the egg can then bury into the wall of the womb (implantation) and develop further.

What happens in ectopic pregnancy?

In an ectopic pregnancy, the implantation process occurs outside of the womb, usually in one of the fallopian tubes. Since this space is not suitable for a baby to develop, the fertilized ovum does not grow into a baby. If not detected in time, an ectopic pregnancy can cause severe complications in the mother and can even kill her.

Normally, the cilia within the fallopian tube help propel the fertilized egg into the womb. If the fallopian tube has been damaged due to obstruction or blockage (due to pelvic inflammatory disease, for example) the fertilized ovum may never reach the womb, instead implanting and developing in the fallopian tube itself.

Risk factors and causes of ectopic pregnancy include:

• Pelvic inflammatory disease (PID) - PID is caused by infection in the genital tract, usually due to bacteria spreading from the vagina or cervix into the womb, fallopian tubes and ovaries.

• Sexually transmitted diseases (STDs) - PID can be caused by several types of bacteria and the presence of an STD such as chlamydia or gonorrhoea can increase the chance of PID developing.  

• Previous ectopic pregnancy - A woman who has already experienced on ectopic pregnancy is at a slightly increased risk of experiencing another ectopic pregnancy in the future.

• Abnormality of the fallopian tube - An abnormity of the fallopian tube such as kinking or scarring may be caused by previous womb infection, PID, previous surgery to the fallopian tube or a sterilization operation.

• Fertility treatments - Infertility treatments that are used to stimulate ovulation can raise the risk of an ectopic pregnancy

• Certain contraceptive devices - The coil or intrauterine device (IUD) can also increase the ectopic pregnancy risk .

• Smoking - Smokers are at a greater risk of ectopic pregnancy

• Age - Women aged over 35 years are at a greater risk

Further Reading

• All Ectopic Pregnancy Content
• Ectopic Pregnancy - What is an Ectopic Pregnancy?
• Types of Ectopic Pregnancy
• After an Ectopic Pregnancy