Background: Short cervix at midgestation, the presence of intraamniotic debris, and cervical funneling are risk factors for preterm birth; however, cervical length measurements and cutoffs are not well documented among pregnant patients of different gestational ages and self-reported races and ethnicities. Objective: This study aimed to describe the distribution of cervical length and frequency of funneling and debris at midgestation in nulliparous women by gestational age and race/ethnicity. Study Design: This secondary analysis of screening data from a multicenter treatment trial of singleton nulliparous patients with short cervix was conducted at 14 geographically distributed, university-affiliated medical centers in the United States. Singleton nulliparous patients with no known risk factors for preterm birth were screened for trial participation and asked to undergo a transvaginal ultrasound to measure cervical length by a certified sonographer. The distribution of cervical length and the frequency of funneling and debris were assessed for each gestational age week (16–22 weeks) and stratified by self-reported race and ethnicity, which for this study were categorized as white, black, Hispanic, and other. Patients enrolled in the randomized trial were excluded from this analysis. Results: A total of 12,407 nulliparous patients were included in this analysis. The racial or ethnic distribution of the study participants was as follows: white, 41.6%; black, 29.6%; Hispanic, 24.2%; and others, 4.6%. The 10th percentile cervical length for the entire cohort was 31.1 mm and, when stratified by race and ethnicity, 31.9 mm for white, 30.2 mm for black, 31.4 mm for Hispanic, and 31.2 mm for patients of other race and ethnicity (P<.001). At each gestational age, the cervical length corresponding to the tenth percentile was shorter in black patients. The 25 mm value commonly used to define a short cervix and thought to represent the 10th percentile ranged from 1.3% to 5.4% across gestational age weeks and 1.0% to 3.8% across race and ethnicity groups. Black patients had the highest rate of funneling (2.6%), whereas Hispanic and black patients had higher rates of intraamniotic debris than white and other patients (P<.001). Conclusion: Black patients had shorter cervical length and higher rates of debris and funneling than white patients. The racial and ethnic disparities in sonographic midtrimester cervical findings may provide insight into the racial disparity in preterm birth rates in the United States.