探讨胎儿MRI检查男性胎儿睾丸下降及发育趋势与其胎龄的关系。

选择2016年7月至2019年3月，胎龄为19~38周时，于四川大学华西第二医院接受产前胎儿MRI检查，并且无泌尿生殖系统异常的1 023例男性单胎胎儿(胎龄为19~23、24、25、26、27、28、29、30、31、32、33、34、35、36、37及38周的胎儿分别为20、19、32、66、66、81、85、72、86、111、113、124、83、34、17及14例)为研究对象。利用胎儿MRI的T2WI及平衡式快速场回波(B-TFE)序列，在冠状位、失状位或轴位任意2个平面，观察胎儿阴囊内单侧和双侧睾丸下降及发育趋势。胎儿左、右侧睾丸下降时胎龄比较，采用成组t检验。将不同胎龄胎儿的双侧睾丸下降率与其胎龄进行曲线拟合。本研究遵循的程序符合2013年新修订的《世界医学协会赫尔辛基宣言》要求。

①本组1 023例胎儿中，20例胎龄为19~23周胎儿的MRI结果，均未见其睾丸下降至阴囊；至胎龄为24⁺¹周时，仅观察到1例胎儿的单侧睾丸下降至阴囊。245例胎龄为25~28周胎儿的MRI结果，可见双侧睾丸下降率变化明显。胎龄为25、26、27及28周时，MRI可见胎儿双侧睾丸下降率分别为28.1%(9/32)、31.8%(21/66)、62.1%(41/66)、83.9%(68/81)；385例胎龄为33~38周胎儿的双侧睾丸下降率为100.0%。②本组1 023例MRI检查结果显示，49例(4.79%)胎儿双侧睾丸下降状态不一致(仅单侧睾丸下降至阴囊)。MRI检查可见左侧睾丸下降至阴囊的胎儿(n＝886)胎龄为(31.6±3.0)周，右侧睾丸下降至阴囊的胎儿(n＝875)胎龄为(31.7±2.9)周，并且差异无统计学意义(P>0.05)；左侧睾丸未下降至阴囊的胎儿(n＝137)胎龄为(25.7±2.5)周，右侧睾丸未下降至阴囊的胎儿(n＝148)胎龄为(25.7±2.3)周，差异亦无统计学意义(P>0.05)。③将不同胎龄胎儿的双侧睾丸下降率与其胎龄进行曲线拟合结果显示，最优拟合模型为二次多项式曲线拟合模型，其模型表达式为y＝-943.79+61.23x-0.89x²，其中y为不同胎龄胎儿双侧睾丸下降率(%)，x为胎儿胎龄(周)。

MRI检查可直观了解男性单胎胎儿睾丸下降与发育趋势。胎儿睾丸下降有一定规律，始于胎龄为24周，胎龄为33周后，其睾丸几乎均下降至阴囊内；部分胎儿存在双侧睾丸下降状态不一致。

To explore the trend of fetal testicular descent and its relationship with gestational age by fetal MRI.

A total of 1 023 cases of male singleton fetuses who underwent prenatal fetal MRI examination in West China Second University Hospital, Sichuan University from July 2016 to March 2019 with gestational age of 19 to 38 weeks and without abnormal genitourinary system were retrospectively analyzed. There were 20, 19, 32, 66, 66, 81, 85, 72, 86, 111, 113, 124, 83, 34, 17 and 14 fetuses respectively with gestational age of 19-23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37 and 38 weeks. The descending and developmental trend of unilateral and bilateral testes in scrotum of fetuses were observed on T2WI and balanced-turbo field echo (B-TFE) sequence of fetal MRI, and testicular descent was confirmed on any two planes in coronal, aberrant or axial position. Gestational age of left and right testicular descent was compared by independent-samples t test. The decline rate of bilateral testis in fetuses of different gestational ages and their gestational age were curve-fitted. This study was in line with requirements of the World Medical Association Helsinki Declaration revised in 2013.

①Of the 1 023 fetuses, testis was not observed in scrotum of 20 fetuses with gestational age of 19 to 23 weeks by MRI. Unilateral testicular descent was first observed in scrotum of a fetus with gestational age of 24⁺¹ weeks. Bilateral testicular descent rate of 245 fetuses with gestational age of 25-28 weeks changed significantly. The rates of bilateral testicular descent were 28.1% (9/32), 31.8% (21/66), 62.1% (41/66), and 83.9% (68/81) respectively in fetuses with gestational age of 25, 26, 27 and 28 weeks. Bilateral testicular descent rate was 100.0% (385/385) in fetuses with gestational age of 33-38 weeks. ②Of the 1 023 fetuses, 49 cases (4.79%) showed that the status of bilateral testicular descent was inconsistent (only one side of testicle descended to scrotum). MRI showed that gestational age of fetuses (n=886) with left testis descending to scrotum was (31.6±3.0) weeks, and gestational age of fetuses (n=875) with right testis descending to scrotum was (31.7±2.9) weeks, the difference was not statistically significant (P>0.05). MRI showed that gestational age of fetuses (n=137) whose left testis did not descend to scrotum was (25.7±2.5) weeks, and gestational age of fetuses (n=148) whose right testis did not descend to scrotum was (25.7±2.3) weeks, and the difference was not statistically significant (P>0.05). ③Curve fitting results of fetal bilateral testicular descent rate and fetal gestational age showed that the best fitting model was a quadratic polynomial curve model, and its expression was y=-943.79+ 61.23x-0.89x², in which y referred as fetal bilateral testicular descent rate of fetuses with different gestational ages (%), and x referred as gestational age of fetuses (weeks).

MRI detection can directly observe the testicular descent and development trend of male singleton fetuses. Fetal testicular descent has a certain regularity, which begins at gestational age of 24 weeks and almost completely descends into scrotum at gestational age of 33 weeks. Some fetuses have inconsistent bilateral testicular descent.