The site of ectopic pregnancy can affect the clinical syndrome of patients. Compared with tubal pregnancy, ovarian pregnancy ruptures more easily, which leads to a higher shock rate and requires more emergency management . The mortality rate of abdominal pregnancy is eight times higher than that of tubal pregnancy, with a mortality rate of 0.5–18% for late diagnosis and treatment [4, 5]. Having a clear picture of the distribution of ectopic pregnancy can help us better make clinical decisions when we encounter a patient with an ectopic pregnancy.
However, the site of ectopic pregnancy has been insufficiently studied. Most studies focus on the trend of the ectopic pregnancy ratio of all female populations or focus on the mortality rate of one specific type of ectopic pregnancy. Tubal pregnancy is the most common type of ectopic pregnancy. According to previous studies, approximately 95% of ectopic pregnancy is tubal pregnancy , ovarian pregnancy makes up approximately 0.5%-3% of ectopic pregnancy with an incidence rate of 1/7000–1/40,000 live births [7,8,9], abdominal pregnancy makes up about 1.3% of ectopic pregnancy with an incidence rate ranging from 1 in 10,000 to 30,000 pregnancies [10, 11], cervical pregnancy comprises about 1% of ectopic pregnancy with an incidence rate varying between 1 in 2,500 and 1 in 12,422 pregnancies [12, 13], and caesarean scar pregnancy makes up approximately 6% of ectopic pregnancy with an incidence rate of approximately 1 in 2500 to 1 in 1800 of pregnancies [14, 15]. Most studies only focus on a specific type of ectopic pregnancy, and we can only obtain general information about the ectopic pregnancy distribution. According to our data, tubal pregnancy consists of 84.70% of ectopic pregnancy cases, which is lower than the 95% reported in previous studies. The proportions of ovarian pregnancy, abdominal pregnancy, cervical pregnancy, caesarean scar pregnancy and cornual pregnancy are close to those in previous studies.
According to the study by Bouyer  in 2001, interstitial pregnancy accounted for 2.4% of ectopic pregnancy, isthmic pregnancy consisted of 12%, ampullary pregnancy accounted for 70%, fimbrial pregnancy comprised 11.1%, ovarian pregnancy accounted for 3.2% and abdominal pregnancy comprised 1.3%. According to our data, interstitial pregnancy consisted of 3.39%, isthmic pregnancy consisted of 4.82%, ampullary pregnancy accounted for 89.21%, and fimbrial pregnancy accounted for 2.58%.
With the increase in the caesarean delivery rate in China, the incidence rate of caesarean scar pregnancy has been increasing in recent years. Caesarean scar pregnancy is a special type of ectopic pregnancy in which embryos are implanted at caesarean scar. Caesarean scar pregnancy can lead to severe complications, such as severe haemorrhage and uterine rupture . According to the study by Li Hong-Tian , during the years 2008–2018, the caesarean delivery rate increased from 28.8 to 36.7%.
The proportion of tubal pregnancy showed a downward trend, the proportions of caesarean scar pregnancy and cornual pregnancy showed an upward trend. From 2012 to 2015 and 2016–2019, the proportion of caesarean scar pregnancy increased from 5.74 to 11.81%, which reminds us that the caesarean delivery rate should be decreased to decrease the morbidity of caesarean scar pregnancy.
From 2012 to 2015 and 2016–2019, the ratio of tubal pregnancy to ectopic pregnancy decreased from 90.06 to 80.98%. This may be because of the rise in women’s health awareness, which leads to a decrease in the rate of pelvic inflammatory disease and tubal diseases. According to the study by Kreisel , the ratio of emergency department visits due to pelvic inflammatory disease decreased from 0.57% in 2006 to 0.41% in 2013. In addition, patients are more willing to treat tubal infertility, which also leads to the decrease in tubal diseases.
The ratio of cornual pregnancy to ectopic pregnancy increased from 1.89 to 3.58%, which may be related to the increase in intrauterine operations and the damage to the endometrium due to those operations. It’s important to decrease the number of unnecessary intrauterine operations.
Caesarean scar pregnancy means a fertilized ovum implants at the caesarean scar. After implantation, trophoblasts can invade the myometrium and grow there, which may lead to uterine rupture or massive bleeding. If it keeps growing, caesarean scar pregnancy can develop into placenta previa, placenta implantation and dangerous placenta previa, bringing great risks to pregnant women . Placenta previa, placenta implantation and dangerous placenta previa may lead to massive haemorrhage, infection, premature delivery, fetal asphyxia, shock and death. Blood transfusion, caesarean, and even hysterorrhexis may be needed to save lives.
Caesarean scar pregnancy is highly associated with a caesarean delivery history, but the pathogenesis is still unclear; its pathogenesis may be the broadening of the scar, fibrosis and ischaemia of the uterine wall, and poor healing of the scar . According to previous studies, high-risk factors for caesarean scar pregnancy are abortion history, multiple caesarean delivery history, suture method and the intervals between caesarean deliveries . The scars of patients with double-layer sutures are thicker than those of patients with one-layer sutures . This is in accordance with the data at our hospital. A total of 72.78% (246/338) of patients had one caesarean delivery, 25.15% (85/338) had two caesarean deliveries, and 2.07% (7/338) had three caesarean deliveries. A total of 80.18% (271/338) had aborted before.
According to the study by So Yun Kim , the mean age at which caesarean scar pregnancy occurs is 35.7 ± 3.8 years old, the mean gestational age at diagnosis is 6.5 ± 1.1 weeks and the mean hCG level before treatment is 30,785 (range 550–155,356) U/L. According to Lanrong Luo , the mean age of individuals with caesarean scar pregnancy is 34.16 ± 4.4 years old. According to our data, the mean age was 32.90 ± 4.80 years old, 67.16% (227/338) of patients were between 30 and 39 years old, and the mean gestational age was 6.67 ± 1.82 weeks, which is similar to previous studies.
The diagnosis of caesarean scar pregnancy is mainly through ultrasound tests, especially transvaginal ultrasound combined with transabdominal ultrasound, Magnetic Resonance Imaging can be used to clarify the relationship between the gestation sac and other organs when necessary. The main clinical manifestations of caesarean scar pregnancy are amenorrhea, abdominal pain and vaginal bleeding , similar to other kinds of ectopic pregnancies. According to our data, the most common clinical manifestations are amenorrhea (98.52%), abdominal pain (25.74%) and vaginal bleeding (67.76%), and the most common sign is uterine enlargement (46.75%).
The main treatment methods for caesarean scar pregnancy are suction curettage, suction curettage + uterine artery embolization, hysteroscopy, hysteroscopy + uterine artery embolization and laparoscopy. Uterine artery embolization can greatly reduce the possibility of massive haemorrhage. It can also be treated by conservative treatment methods, using localized or systematic methotrexate . At our hospital, 40.23% (126/338) of patients were treated by suction curettage, and 37.28% (126/338) of patients were treated by suction curettage + uterine artery embolization. Suction curettage and suction curettage + uterine arterial embolization are the dominant treatment methods.