Abstract: Objective To observe the prenatal diagnosis of fetal sex chromosome mosaicism and chromosome polymorphism for pregnancy outcome. 
Methods We selected 400 pregnant women in the middle and late stages of pregnancy who underwent diagnosis and treatment in the First Affiliated Hospital of Air Force Medical University, and underwent amniocentesis for analysis of amniotic fluid chromosome karyotype. The distribution of different types of abnormal karyotypes was observed, and the distribution of sex chromosome mosaicism was analyzed. Chromosomal polymorphism distribution and pregnancy outcomes were recorded. 
Results Among the 58 abnormal karyotypes, 39 patients (67.24%) had abnormal chromosome number, and the most common was trisomy 21 syndrome, including 14 patients (24.15%). There were 12 patients (20.69%) with chromosome Mosaic type, 19 patients (32.76%) with abnormal chromosome structure, as well as 8.62% patients with inversion and 6.89% with translocation. A total of 11 patients with sex chromosome mosaicism were detected, including 9 patients with 45,X mosaicism and 2 patients with other types of chromosomes. The most common indication for prenatal diagnosis was amniotic fluid karyotype verification. Through follow-up observation, 9 patients chose to terminate pregnancy, and 1 patient had blurred genitalia after induced labor. Two pregnant women with low proportion fetal karyotype of sex chromosome mosaicism 45,X［3］/46,XX［97］ and 45,X［4］/46,XX［65］ continued their pregnancy and delivered a full-term female neonate by cesarean section, and the physical status and IQ indexes of the neonate were normal. Through the follow-up observation of pregnancy outcomes, except 32 patients with chromosome polymorphism who were lost to follow-up, there were 4 patients with pregnancy termination due to fetal structural abnormalities, and 22 patients with continued pregnancy. Among the pregnant women who continued the pregnancy, 19 neonates had normal physical and intellectual health, and only 3 neonates had abnormalities after birth. 
Conclusion Prenatal diagnosis can be performed by amniocentesis and chromosome karyotype analysis of amniotic fluid to inform pregnant women of possible abnormalities in the fetus, so as to avoid the birth of children with chromosome abnormalities, ensure the health of the fetus after birth, and reduce the burden of society and family. 

Key words: sex chromosomes, prenatal diagnosis, pregnancy outcome