Ectopic pregnancy can occur after natural conception, with an incidence of about 1–2%, or after undergoing an assisted reproductive technique, with an incidence described as up to four times higher.
One of the main factors that may increase the risk of ectopic pregnancy is the tubal factor, when the fallopian tube is damaged due to pelvic inflammatory disease, previous surgery, and so on. However, tubal factor infertility is one of the common reasons why a couple may resort to assisted reproduction in order to achieve pregnancy. For this reason, it is expected that the incidence of ectopic pregnancy with assisted reproductive techniques, especially IVF, will be higher.
Similarly, endometriosis has also been associated with an increased risk of ectopic pregnancy due to the possible presence of endometrial tissue in the fallopian tubes.
On the other hand, maternal age over 35 years may also increase the likelihood of ectopic pregnancy. In this case, it is important to mention that the decline in fertility with maternal age is one of the main reasons for turning to assisted reproductive techniques.
For all these reasons, some experts believe that assisted reproductive techniques do not in themselves increase the risk of ectopic pregnancy, but that the risk appears higher compared to natural conception because of the underlying infertility that leads the couple to use them.
However, despite what has just been mentioned, several factors have been proposed that could increase the risk of ectopic pregnancy in an in vitro fertilization cycle:
- Day-3 transfer: when an embryo is transferred on day 3, the time that elapses before potential implantation is longer than when a blastocyst is transferred. Therefore, the possibility increases that the embryo may reach the fallopian tube.
- Transfer of more than one embryo: this may be related to day-3 transfer, as it used to be more common to transfer several embryos on day 3 of development. However, nowadays, the tendency is to transfer a single embryo at the blastocyst stage.
- Fresh transfer: the explanation would be that high hormone and estrogen levels during ovarian stimulation may create a tubal and uterine environment that favors ectopic pregnancy. Thus, vitrifying embryos and transferring them later could prevent this negative effect. The same would apply if the treatment is an egg donation cycle. Since the patient does not undergo ovarian stimulation, the potential risk of ectopic pregnancy would be lower.
- Thin endometrium: a thinner endometrium may be associated with a uterine lining less favorable for implantation, which could encourage the embryo to implant elsewhere. In contrast, an endometrium with adequate thickness could be a protective factor against ectopic pregnancy.
