Abstract: Objective To study the application of fetal cord blood chromosomal karyotype analysis in prenatal diagnosis of the third trimester fetuses. Methods Fetal cord chromosomal karyotypes from 52 pregnant women admitted to our hospital from January 2012 to December 2012 with indications for umbilical cord puncture at weeks 17-39 after pregnancy were analyzed. Results Among the 14 pregnant women with abnormal choromosomal karyotypes detected in their cord blood (the abnormal rate of choromosomal karyotypes was 26.9%), trisomy 21 was detected in 7, trisomy 18 in 2，partial trisomy in 2, chromosomal translocation in 1, chromosomal inversion in 1 and Turner syndrome in 1, accounting for 50%, 14.3%, 14.3%, 7.1%, 7.1%, 7.1% respectively of the abnormal choromosomal karyotypes. Conclusion Fetal cord blood chromosomal karyotype analysis is not limited by the pregnancy time and can effectively reduce the rate of birth defects, thus playing an important role in prenatal diagnosis of the second and third trimester fetuses.