The group carrying the β thalassemia gene (β+, β0 and β thalassemia combined with α thalassemia) all had an average increase in HbA2 rate of 5%; Regarding fetal globin gene mutation characteristics: 21.8% did not carry globin gene mutations, 55.2% heterozygous (heterozygous carriers), 23% of fetuses are affected; With the α - thalassemia gene mutation, the - -SEA mutation is the most common, the other mutations are less common: - α3.7, HbCs, - α4.2; detected 2 cases of rare mutation in Vietnamese (C2del T).