Objective To investigate the manifestations and clinical application of magnetic resonance imaging (MRI) in the diagnosis of pelvic tumors during pregnancy.Methods Clinical data and MRI manifestations of 161 patients attending Women's Hospital,School of Medicine,Zhejiang University with pelvic tumors during pregnancy between March 2013 and July 2016 were retrospectively analyzed.MRI manifestations and clinical treatments of different tumors in pregnancy were summarized.All data were analyzed by descriptive statistics.Results (1) The gestational ages at initial diagnosis of the 161 patients ranged between 8-39 weeks and the average gestational age was (29±-4) weeks.Of all patients,147 (91.3％) had benign tumor,while the other 14(8.7％) were diagnosed as malignanices.The sensitivity,specificity and accuracy of MRI in the diagnosis of malignancy during pregnancy were 92.8％ (13/14),97.3％ (143/147) and 96.7％ (156/161).Uterine neoplasm,ovarian tumor,intestinal tumor and pelvic peripheral nerve schwannoma respectively accounted for 67.1％ (108/161),29.8％ (48/161),1.9％ (3/161) and 1.2％ (2/161) of all cases.(2) Among the 108 gravidas with uterine neoplasm,104 cases of leiomyoma continued to term pregnancy,among which 71 underwent myomectomy after vaginal delivery and 33 had myomectomy during cesarean section;the other four cases of cervical cancer terminated their pregnancy.(3) Among the 48 gravidas with ovarian tumor,38 were diagnosed as having benign tumor by MRI and continued to term pregnancy;five were diagnosed with tumor pedicle torsion and treated with emergency operation because of acute abdominal disease;two patients who were both in their second trimester (16 and 20 gestational weeks) were diagnosed with ovarian cancer complicated with peritoneal metastasis by MRI and decided to terminate pregnancy;another two patients with uncertain preoperative diagnosis of ovarian cancer were followed up closely to term and the tumor was removed during cesarean section;one patient with ovarian malignant tumor,which was diagnosed by MRI at the 32nd gestational week,received cesarean section and cytoreductive surgery.(4) In the three gravidas with intestinal tumor,one was complicated with sigmoid colon cancer and underwent cesarean section,radical resection of sigmoid colon tumor,colostomy and enterodialysis at 28+3 weeks of gestation;one with appendiceal mucinous adenocarcinoma was monitored closely until full-term pregnancy and received right hemicolectomy during cesarean section;the third case with malignant stromal tumor of the small intestine underwent cesarean section at 30+5 weeks of gestation as well as the completer resection of tumor.(5) One gravida with pelvic peripheral nerve schwannomas was diagnosed with pelvic schwannoma and underwent cesarean section and tumor extirpation at term.The other one underwent tumor extirpation prior to delivery due to the larger size of tumor and had a vaginal delivery at term.Conclusions MRI can provide more precise information for prenatal diagnosis of pelvic tumors during pregnancy.