Abdominal pregnancies are very rare, constituting about 0.9-1% of all ectopic pregnancies. Occurring in one in every 3,371 to 10,200 deliveries, it is about 8 times likely to cause death than tubal pregnancies and about 90 times likely to cause death than normal pregnancies.
Classified into primary and secondary abdominal pregnancies, primary abdominal pregnancies are those that implant primarily in the abdomen, while secondary abdominal pregnancies are those that re-implant in the abdominal cavity after being extruded from more commonly a tubal ectopic site. Another possible site of extrusion is from the uterus via a small rupture created by intra-uterine instrumentation for example during IVF. Common implantation sites are in 1) the pouch of Douglas (POD), which is the space behind the womb, 2) the space between the bladder and the uterus, 3) the space between the uterus and the adnexa, 4) on the omentum and 5) on the bowels. Implantations on the liver and spleen have also been reported.
Secondary abdominal pregnancies are commoner than primary abdominal pregnancies and share similar risk factors with tubal pregnancies. They include pelvic inflammatory disease (PID), IVF and endometriosis. The risk factors for primary abdominal pregnancies are unknown.
Abdominal pregnancies may be difficult to distinguish from normal pregnancies as they can progress into the 2nd and 3rd trimester without symptoms while complications may occur very late into the pregnancy.
The symptoms may include recurrent abdominal discomfort, excessive fetal movement beneath the abdominal wall, and presence of fetal movements high up in the upper abdomen. Others are occurrence of vomiting late in the pregnancy, as well as abnormal position of the unborn baby at term. At term, there is always a failure of initiation of labor, whether spontaneously or by induction.
Due to sudden fetal death in about 75 to 95% of cases, sudden cessation of fetal movement is common.
Often times, it may be detected during surgery i.e. intra-operatively, where it is commonly associated with massive bleeding from the point of placenta implantation on the intestines and abdominal organs and is often associated with a high rate of complications and a significant risk of death (4% to 29%).
Diagnosis before complications involves a high index of suspicion. A detailed clinical history, a thorough clinical examination and a detailed ultrasound scan by an experienced sonologist may help to clinch the diagnosis before term or before the onset of symptoms. Another imaging modality that may help to clinch the diagnosis is the MRI.
Once detected, a termination of the pregnancy is highly recommended upon diagnosis especially when the pregnancy is below 20 weeks, given the extremely high risk of maternal death. Delaying the delivery till about 34 weeks may be considered when the diagnosis is made after 20 weeks of gestation in a healthy patient who can be monitored very closely in a tertiary care centre, if congenital abnormalities of the fetus can be excluded by an ultrasound scan and the placenta is implanted far away from the upper abdomen. At surgery, the placenta is usually left in place due to the high risk of severe bleeding associated with tampering with it, where it is expected to gradually get absorbed. Medications are usually given to hasten the breakdown of the placenta tissue and antibiotics to prevent infection within the abdomen and the pelvis.
Though surgical modality of management is the main stay of management, medical management are increasingly employed with or without surgical modality of management as more and more cases are being diagnosed early in pregnancy with the aid of more modern ultrasound scans with improved image clarity.
Medical management with systemic methotrexate (MTX) and/or local injections of MTX or potassium chloride (KCl) have been reported, although nearly half of these may require subsequent surgical management due to failure of the medical management.
The operative approach however must be tailored to the patient’s clinical presentation and stability, and the location of the ectopic pregnancy. Options include laparoscopy with or without prophylactic embolization of the placental bed for clinically stable patients in early pregnancy and laparotomy with or without prophylactic embolization and post operative methotrexate injection to help destroy the placenta bed in late pregnancy. Due to heavy bleeding, intra-operative blood transfusion is common. The most common post operative complication is pelvic abscess and infection from the left over placenta tissue.
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