-CAUSES AND RISK FACTORS
This is a rare complication of multiple pregnancies in which there is a simultaneous occurrence of an ectopic pregnancy with a normal pregnancy. In heterotopic pregnancies, 97% of the ectopic pregnancies are located in the fallopian tubes, while the rest are rarely located in the ovary, cervix and the abdomen. Even more rarely, cases of multiple ectopic pregnancies, with two or more embryos implanted in one or both fallopian tubes have been recorded with a normal pregnancy i.e. a triplet heterotopic pregnancy.
Theoretically, heterotopic pregnancies are estimated to occur in 1:30,000 pregnancies; it is very rare in natural conception i.e. pregnancy conceived naturally without fertility treatment but its incidence has increased significantly thanks to assisted reproductive technology (ART) such as invitro-fertilization (IVF) with a rate quoted to range between 1:100 to 1:500 following ovulation induction, and in about 5% of pregnancies achieved by IVF.
CAUSES AND RISK FACTORS
While patients with heterotopic pregnancies share similar risk factors with patients at risk of ectopic pregnancy, it is obvious from the above statistics that the most important risk factors other than a patient’s background risk factor for ectopic pregnancy are:
1. Controlled Ovarian Stimulation/ Ovulation induction
The use of ovarian stimulating drugs increases the number of eggs available for conception. Since heterotopic pregnancy occur only in the context of multiple pregnancies, it is therefore quite obvious the relationship that exist between heterotopic pregnancy and controlled ovarian stimulation and ovulation induction.
2. Embryo transfer
Probably the most important risk factor till date is the process of embryo transfer during IVF. In fact a quoted risk of one heterotopic pregnancy in 45 embryo transfer has been reported for ART cycles associated with transfer of 4 or more embryos into the mother’s womb. Possible reasons why this may happen include inadvertent placement of the tip of the embryo transfer tube or catheter, close to the fallopian tubes, excessive force or large volume of transfer, resulting in retrograde or upward flow of the embryos into the fallopian tubes. Another possible explanation is the retrograde or upward migration of an embryo due to uterine contractions that propel an embryo into the fallopian tube.
Therefore, if you have an ART cycle with embryo transfer, your doctor will routinely do an early scan to exclude an ectopic pregnancy and or a heterotopic pregnancy, if your pregnancy test comes out positive about two to three weeks after the procedure.
This may vary from one patient to the other but among patients, a high index of suspicion must be maintained until the disease is either confirmed or refuted especially in patients at high risk of developing heterotopic pregnancy. They include:
1. In about 50% of patients, there is absolutely no symptoms until the fallopian tube ruptures.
2. Pregnancy symptoms; such as vomiting, nausea e.t.c.
3. Abdominal pain which may vary from mild to severe pain.
5. Fainting attacks
6. Due to a co existing normal pregnancy, the incidence of vaginal bleeding is although greatly reduced, vaginal bleeding may still occur.
11. Pelvic adhesions
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1. Heterotopic pregnancy: A diagnosis we should suspect more often. Karim MH, Abderrrahim EB, Mohammed K, Khalid M. J Emerg Trauma Shock. 2010 jul-sep; 3(3): 304. PMCID: PMC2938513.
2. Alsunaidi MI. An unexpected spontaneous triplet heterotopic pregnancy. Saudi Med J.2005:26:136-8.
3. Williams Obstetrics Twenty-Second Ed. Cunningham, F. Gary, et al, Ch. 10. MedlinePlus [Internet]. Bethesda (MD): National Library of Medicine (US); [updated 2006 Feb 21]. Ectopic Pregnancy; [updated 2010 Feb 21;] Available from http://www.nlm.nih.gov/medlineplus/ency/article/000895.ht