图示输卵管妊娠破裂，图左可见双胞胎胎儿，紧邻破例处的血凝块。半数的异位妊娠的病因是盆腔炎症性疾病导致的慢性输卵管炎，或由阑尾炎、子宫内膜异位症或以前的手术导致的炎症。然而也有很多病例病因不明。
异位妊娠模式图 | 输卵管妊娠:双胞胎(大体) | 破裂切除标本(大体) | 出血(镜下) | 示血凝块和胎盘绒毛(镜下)
This is a ruptured tubal ectopic pregnancy. Note the twin fetuses at the lower right adjacent to the blood clot at the left. About half of ectopic pregnancies occur because of an identifiable lesion such as chronic salpingitis from pelvic inflammatory disease or adhesions from appendicitis, endometriosis, or previous laparotomy. However, in half of cases no cause can be found.