A Caesarean Scar ectopic pregnancy is a non-tubal ectopic pregnancy and is one of the rarest forms of ectopic pregnancies. However with caesarean sections being one of the most common operations performed in the developed world and the number of women having caesarean sections increasing, the incidence of caesarean scar ectopic pregnancies is also increasing.
A caesarean scar ectopic pregnancy occurs when the pregnancy implants in the lower part of the uterus, on the scar performed at the time of a caesarean section. The concern with a caesarean scar ectopic pregnancy, is that if the pregnancy continues, the placenta will become deeply embedded within the scar and in some cases may continue through the scar and grow towards the bladder. This can result in rupture of the womb in the most severe cases. It is extremely rare that a caesarean scar ectopic pregnancy will continue and cases lasting to the third trimester are associated with a morbidly adherent placenta and a high risk of severe bleeding as the placenta fails to deliver, resulting in a caesarean hysterectomy to control the bleeding.
The symptoms of a caesarean scar ectopic pregnancy can be very similar to that of a miscarriage and most women commonly present with vaginal bleeding and/or abdominal discomfort in early pregnancy. However in some circumstances, the women may be asymptomatic. Profuse vaginal bleeding and acute abdominal pain is a rare presentation and in women who are haemodynamically unstable, there should be a strong suspicion of uterine rupture with intra-abdominal bleeding.
Accurate diagnosis is essential and pelvic ultrasound imaging is the diagnostic tool of choice. The characteristic features of a caesarean scar ectopic pregnancy on ultrasound imaging are the presence of a gestational sac attached to the scar of a previous caesarean section. The gestational sac may be on the endometrial cavity side or completely in the scar surrounded by the myometrium, and can contain a yolk sac and embryo with or without cardiac activity. The ultrasound criteria for the diagnosis of a caesarean scar ectopic pregnancy are as follows;
- Empty uterine cavity and closed and empty cervical canal,
- Placenta and/or a gestational sac embedded in the scar of a previous caesarean section,
- A triangular, round or oval-shaped gestational sac that fills the niche of the scar,
- A thin or absent myometrial layer between the gestational sac and the bladder,
- Yolk sac, embryo and cardiac activity may or may not be present,
- Evidence of functional trophoblast/placental circulation on colour flow Doppler examination, characterised by high velocity and low impedance blood flow,
- Negative ‘sliding organs’ sign.
Once a caesarean scar ectopic pregnancy is diagnosed, it would be advised that it is not safe to continue with the pregnancy due to the high risk of serious complications to the mother. This can be a difficult decision for the woman, especially as in some cases the pregnancy may still be alive.
There is currently insufficient evidence to recommend one way of managing a caesarean scar ectopic pregnancy over another, however the current consensus in the UK supports surgery as the most effective treatment. The surgical treatment is similar to that when we treat a miscarriage. A small suction catheter in introduced into the womb through the cervix and the pregnancy tissue is gently removed under ultrasound guidance. Due the potential risk of heavy bleeding at the time of surgery, a small catheter may be placed in the cervix to reduce the risk of bleeding.
The majority of women will go on to have a normal pregnancy following a caesarean scar ectopic pregnancy, with risk of recurrence reported to be 3-5 per 100 women.