The most common cause of ectopic pregnancy is malformation, narrowing, or ostruction of any of the fallopian tubes that prevents the embryo to descend and make its journey to the uterus.
There are also other factors that may cause an ectopic pregnancy, like smoking and the use of some contraceptives. The risk of suffering an ectopic pregnancy is doubled up when a women smokes more than 20 cigarrettes a day. This risk is due to the toxic effect of nicotine in the Fallopian tubes.
On the other hand, we have the contraceptive pills. Containing hormones such as progesterone or estrogens, they may slow down the embryo’s journey through the Fallopian tubes.
The intrauterine device (IUD) can increase the risk of having a pelvic infection or a tube inflammation, indirectly increasing the risk of ectopic pregnancy. The progesteron-releasing devices can also slow down the movement of the embryo through the tubes.
The pelvic inflammatory disease (PID), also known as salpingitis, can be a byproduct of a sexually-transmitted disease (STD). The most common agent causing it is a type of chlamydia known as the Chlamydia trachomatis.
This disease presents inflammation of the pelvic structures, the uterus and the fallopian tubes. Such inflammation provokes a mechanical impediment that prevents the embryo to move towards the uterus. This clinical antecendent is in 50% of the ectopic pregnancies.
The hormonal imbalances provoked by the antiestrogen action of the clomiphene citrate in ovulation induction treatments may provoke alterations in tubal motility.
The existence of previous ectopic pregnancies mutiplies 7 to 10 times the risk of ectopic pregnancy, although this factor is commonly associted with another causes.
The tubal ligation or a subsequent tubal reconduction may increase the risk of suffering an ectopic pregnancy, just as another surgeries like appendectomy, which may provoke the development of peritoneal adherences.
The development of assited reproductive techniques entails the development of a new risk factor.
If we focus on the ectopic pregnancies provoked by assisted reproduction techniques, especially the in vitro fertilisation, either by conventional IVF or ICSI, the reason why the embryos can move outside the uterine cavity is, to a certain extent, due to the technique itself. The volume of the transferred fluid, the placement of the cannula transfer in the uterine bottom, and the uterine manipulation may also have an influence.