To evaluate the clinical and ultrasonic features of fetal sacrococcygeal teratoma (SCT) of different histological types.

A retrospective analysis was performed on a total of 34 patients with SCT that was diagnosed from January 2015 to December 2016 at Beijing Obstetrics and Gynecology Hospital, Capital Medical University. These cases were divided into either a mature group or an immature group based on the histological type. Data (maternal age, gestational weeks, and tumorous sonographic features) were analyzed by the Fisher exact test, t-test, Chi-square, and Mann-Whitney U test.

No statistical differences were observed in terms of maternal age, gestational week, fetal sex, and Altman's classification between the mature (n=23) and immature groups (n=11). Among all the ultrasonic features, mass volume of the immature group was significantly bigger than that of the mature group [16.19 (8.47, 34.03) cm³ vs 186.20 (90.41, 445.35) cm³, Z=-3.332, P=0.001]. The main manifestation of the mature group was cystic echo (56.5%, 13/23), while that of the immature group was cystic-solid echo (100%, 11/11); the difference between the two groups was statistically significant (P=0.002). Color Doppler ultrasound showed that three cases in the mature group and ten cases in the immature group were detected with blood flow signal; the difference in the number of cases with blood flow signal was statistically significant between the two groups (P＜0.001). Scanning of the tissues surrounding the mass and other fetal systems showed that five cases in the mature group and seven cases in the immature group suffered from complications; there was a statistically significant difference between the two groups (P=0.026).

The clinical features and prenatal ultrasonic images of fetal SCT vary with different pathological types. Cystic-solid echogenic masses, bigger mass volume, rich blood flow signals, and suffering from complications are important signs for the diagnosis of immature fetal SCT. Early diagnosis by using prenatal ultrasound can provide a good basis for perinatal management.