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To determine the significance of polydactyly identified on prenatal ultrasonography and provide a detailed analysis of characteristics and perinatal outcomes of fetal polydactyly. This is a retrospective cohort study of pregnancies with a postnatal diagnosis of fetal polydactyly between January 2016 and December 2023. The population was divided into 2 groups at postnatal diagnosis: the isolated polydactyly group and the nonisolated polydactyly group. Clinical data, prenatal ultrasonography, related genetic results, and postnatal outcomes were obtained. Our study cohort comprised 328 fetuses with polydactyly. The overall detection rate of polydactyly by prenatal ultrasound was 19.2%, and the first detection rate in the first‐, second‐, and third‐trimester were 0.9%, 14.6%, and 3.7%, respectively. Preaxial polydactyly (PPD) of hand was the most common type and the most common type of foot polydactyly was postaxial polydactyly (PAP) both in the isolated group and in the nonisolated group; the central polydactyly is rare. Syndactyly was the most common abnormality complicated with polydactyly. Between the nonpolydactyly group, the isolatedpolydactyly group and the nonisolated polydactyly group, there was a significant difference in perinatal outcome (P< .001). The second trimester is the best gestational age for prenatal ultrasound detection of polydactyly. Polydactyly of hand was more likely PPD, while polydactyly of foot was more likely PAP. When polydactyly is detected by routine prenatal ultrasound, detailed ultrasound examination and prenatal counseling should be performed to determine the possibility of an underlying genetic syndrome.