In the present study, we summarized the characteristics, treatment and outcomes of AT in pregnant women over 10 years. Eighty-two patients were included. However, considering that the occurrence of AT during pregnancy is uncommon, the number of cases in our study is relatively large. Hasson  et al. described a series of 118 patients with AT during a 10-year period in two tertiary centers, of which 41 patients were pregnant. Ginath  et al. reported 54 cases of AT in pregnant women.
The accurate diagnosis of AT is often challenging, as the symptoms and signs of AT during pregnancy lack specificity. Consistent with other studies [13, 14], most cases occurred in the first trimester but could occur even in the third trimester: 8 (9.8%) patients experienced AT in the third trimester. Almost all patients were admitted to the emergency department because of acute or subacute low abdominal pain . Nausea and vomiting was another common manifestation after pain, with an incidence of up to 70% [2, 4, 5, 15]. AT can be misdiagnosed as other diseases that cause lower abdominal pain, such as appendicitis and renal colic . In the present study, three patients underwent laparotomy because of suspected appendicitis and were found to have AT during the operation. In addition, white blood cell counts may be slightly elevated. Chang  et al. reported that 45% of patients had elevated white blood cells. Ginath  et al. also revealed a slight elevation in white blood cell counts in pregnant women with AT compared with nonpregnant women. In our study, 47.6% of patients had leukocytosis, which was consistent with previous studies.
Ultrasound is the most common imaging method for evaluating acute abdominal pain during pregnancy in the emergency department. Color Doppler sonography has been recently proposed as a useful tool for improving the preoperative diagnosis of AT. However, some studies have demonstrated that the Doppler finding has a high false-negative rate. Smorgick  et al. reported that a normal Doppler flow was found in 60% of cases of AT in pregnant women. Hasson  et al. described that only 39% of cases of AT in pregnant women showed no blood flow on the Doppler test. Ginath  et al. reported that Doppler flow examination revealed the lack of arterial flow in 70% of pregnant women. In the present study, 37.5% of the patients had a normal Doppler flow signal. The reason for the high false-negative rate may be that the severity of the vascular impairment is variable, depending on the number of twists, the tightness and the duration of torsion, which can cause partial or complete vascular obstruction. Therefore, the decision regarding surgery should not be made based on the findings regarding blood flow alone but based on the clinical suspicion of AT. In addition, the gravid uterus may displace the twisted mass so that the mass is not detected, which can lead to delayed diagnosis. In our study, ultrasound failed to reveal the twisted mass in 2 patients due to the enlarged uterus. There is increasing evidence that MRI can be used for the primary evaluation of acute abdominal pain in pregnancy, particularly when appendicitis cannot be excluded and a mass is not detected by ultrasound .
Similar to in nonpregnant women, laparoscopy has become a common and safe mode of surgical treatment for AT in pregnant women. Hasson  et al. reported that laparoscopy was performed in 88% of pregnant women with AT. Daykan  et al. conducted a study in which 85 pregnant women with AT were enrolled, and 78 (91.7%) patients underwent laparoscopy. In 2011, the Society of American Gastrointestinal and Endoscopic Surgeons stated that laparoscopy can be safely performed during any trimester of pregnancy and is recommended for the diagnosis and treatment of AT unless the clinical severity warrants laparotomy . Laparoscopy can be performed in the third trimester by experienced surgeons. Chohan  successfully performed laparoscopic surgery for a woman with fallopian tube torsion at 35 weeks of gestation. It has been confirmed that laparoscopic surgery does not affect obstetrical outcomes compared with laparotomy  and does not increase complications such as thromboembolism events, sepsis and spontaneous abortion.
Compared with nonpregnant women with AT, pregnant women were more likely to undergo conservative surgical management. Previous studies have shown that 30% ~ 100% of patients underwent conservative surgical management, and detorsion only was the most common procedure [3, 4, 7, 14]. But in our study, only one patient underwent detorsion only and 48 underwent cystectomy. Interestingly, there was no recurrence in our study during the same pregnancy. This is inconsistent with previously published literatures. Hasson  et al. reported that the rate of recurrence in the same pregnancy of AT for pregnant women who underwent detorsion only was 19.5%. Pansky  et al. described that the recurrence rate of detorsion only was 20% and that there was no recurrence in patients who underwent cystectomy or oophorectomy. Compared with the previous studies, cystectomy may remove the risk factors for recurrence. The twisted adnexal mass has edema and is fragile, which sometimes makes cystectomy difficult. In this situation, detorsion and fenestration for large cysts can be performed safely because most of the cases are benign masses.
Regrettably, more patients (35.5%, 29/82) in our study underwent USO than in previous studies [4, 6, 12, 14]. The decision to perform USO was at the discretion of the surgeon. Based on the descriptions in the surgical records in the present study, physicians preferred to perform USO if the color of the adnexa was still blue-black for ten minutes after detorsion. However, some studies have proven that it is not accurate to determine the activity of the ovary based on the color during the surgery [20,21,22]. Parelkar  et al. presented a case series of 12 children with AT. Although the appearance of the ovaries of 10 patients was found to be severely ischemic during the operation, all underwent detorsion with or without evacuation of the hematoma. Follow-up sonography showed all ovaries had follicular development except one.
Surgical procedures did not affect the obstetric outcomes. In our study, there was no spontaneous abortion after surgery. One patient experienced intrauterine fetal death at 25 weeks of gestation. Wherever the patient underwent oophorectomy at 8 weeks of gestation, fetal loss was not associated with the surgery. Inconsistent with our observation, in a study of the same size, Daykan  et al. reported that the overall postoperative spontaneous abortion rate was 3.5%, but all occurred more than 2 weeks after the surgery, so they were not considered to be related to the surgery. Before the formation of the placenta, removing the ovarian or corpus luteum may decrease the level of progesterone, which maintains the development of the fetus. According to the guidelines of the Society of American Gastrointestinal and Endoscopic Surgeons , progesterone was administered to patients who underwent surgery in the first trimester in our study. This may be the reason for the relatively low rate of spontaneous abortion after surgery.
However, our study also has weaknesses, namely, its retrospective nature and long-time span. The limited sample size and bias caused by a single center analysis may have also affected the results of the study. However, the low incidence rate makes it difficult to collect enough cases to conduct a prospective study.