目的 探讨宜宾地区妊娠18 ~ 40周低风险胎儿直肠壶腹部内径与孕周之间的相关性，并建立参考值范围。 方法 选取2022年10月至2024年3月在宜宾市第二人民医院、宜宾市第一人民医院、宜宾市第五人民医院、宜宾市妇幼保健院、宜宾市翠屏区妇幼保健院等医疗机构建档并规律接受Ⅰ、Ⅱ、Ⅲ级产前超声筛查的妊娠18 ~ 40周低风险单胎孕妇1 103例。通过产前超声测量胎儿直肠壶腹部内径（包括前后径、左右径及面积）。采用Shapiro-Wilk检验进行正态性检验，使用SPSS的“重叠散点图”功能制作胎儿直肠壶腹部内径与孕周变化的散点图，百分位数计算通过SPSS的“探索”功能进行，参考值范围使用P5、P10、P50、P90和P95进行描述。 结果 妊娠18 ~ 20周胎儿直肠壶腹部显示率为61%；妊娠21 ~ 37周显示率为100%；妊娠超过37周的显示率为96%。胎儿直肠壶腹部内径随孕周增加而增大（r = 0.925 ~ 0.949，P < 0.01），差异有统计学意义。 结论 产前超声评估胎儿直肠壶腹部内径参数与孕周之间存在显著相关性。本研究建立的妊娠18 ~ 40周低风险胎儿直肠壶腹部内径参考值范围，可能为宜宾地区产前诊断胎儿直肠肛门疾病提供更多的理论参考依据。

Objective To examine the correlation between fetal rectal ampulla diameter and gestational age， and to establish reference value ranges for low-risk fetuses between 18 and 40 weeks of gestation in Yibin region. Methods A total of 1，103 low-risk singleton pregnant women between 18 and 40 weeks of gestation were recruited from five hospitals in Yibin City （the Second People′s Hospital， the First People′s Hospital， the Fifth People′s Hospital， the Maternal and Child Health Hospital of Yibin City， and the Maternal and Child Health Hospital of Cuiping District） for routine level Ⅰ， Ⅱ， and Ⅲ prenatal ultrasound screening from October 2022 to March 2024. Fetal rectal ampulla diameters， including anteroposterior diameter， transverse diameter， and area， were measured using prenatal ultrasound. The normality of these measurements was assessed using the Shapiro-Wilk test. Scatter plots depicting the relationship between fetal rectal ampulla diameter parameters and gestational age were generated using the "Overlap Scatter Plot" function in SPSS. Percentiles were calculated using the "Explore" function in SPSS， with reference value ranges described by P5， P10， P50， P90， and P95. Results The visualization rate of the fetal rectal ampulla diameter was 55% at 18 ~ 20 weeks of gestation， 100% at 21 ~ 37 weeks， and 96% at greater than 37 weeks. The fetal rectal ampulla diameter exhibited a significant positive correlation with gestational age （r = 0.925 ~ 0.949， P < 0.01）. Conclusions Prenatal ultrasound measurement of fetal rectal ampulla diameter demonstrates a robust correlation with gestational age. The reference intervals for the rectal ampulla diameter of low-risk fetuses between 18 and 40 weeks of gestation， established in this study， may offer valuable theoretical guidance for prenatal diagnosis of fetal rectal and anal abnormalities in Yibin region.