Hemophilia is a bleeding disorder caused by a deficiency of clotting factors, most commonly hemophilia A and hemophilia B. Most of the patients are males who have inherited the disease-causing gene on their mother’s X chromosome, resulting in a deficiency of clotting factor VIII or IX. The disease is inherited in an X-linked recessive manner, which is called “male but not female” in common parlance, meaning that the patients are usually males, because males have only one X chromosome, and as long as there is a relevant gene defect, it will lead to the corresponding clinical manifestations; whereas females have two X chromosomes, and only if there is a relevant gene defect on both X chromosomes will the disease develop. In women, there are two X chromosomes, and the disease will only develop if there are related genetic defects on both X chromosomes, so female patients are very rare. The “male but not female” rule describes only part of the inheritance pattern of hemophilia, and does not mean that a boy is necessarily a patient. A woman with a genetic defect on only one chromosome is called a carrier, and although carriers do not develop the disease, they may pass on the gene to the next generation. Boys are 1/2 patients and 1/2 completely normal; girls are 1/2 carriers and 1/2 completely normal. In order to effectively prevent the birth of children with hemophilia and to avoid pain and financial burden to patients and their families, screening and targeted prenatal diagnosis of female hemophilia carriers are currently the preferred and effective measures in China. Some common consultation questions are summarized as follows: 1. Who needs to receive genetic diagnosis of hemophilia? Women with hemophilia in their immediate family or in their mother’s family are the main targets for clinical genetic diagnosis of hemophilia. Daughters of hemophiliacs are certain carriers. For prenatal screening, it is also recommended that hemophilia-related genetic testing be performed in advance of pregnancy. 2.Whose blood samples are required for hemophilia gene? Hemophilia A requires specimens from three generations of the mother’s family, including the patient; hemophilia B requires specimens from the patient and related subjects only. 3.Can I still do carrier genetic testing if the hemophiliac in my family is deceased? If a positive carrier blood sample is provided (i.e., the patient’s mother or daughter), approximately 90% of hemophilia genetic defects can be detected. 4.How long should I be pregnant for prenatal genetic diagnosis of hemophilia? Whose blood samples are needed? Since hemophilia genetic diagnosis takes a long time, it is recommended to do the carrier test before pregnancy, and if you are identified as a carrier, you can choose to have your fetus prenatally diagnosed by taking chorionic villus at around 11 weeks or amniotic fluid at around 18 weeks after pregnancy. 5.How long does it take for the report of genetic diagnosis and prenatal diagnosis? Given the complexity of hemophilia genes and the limitations of diagnostic technology, the genetic diagnosis results of the disease take a long time. It takes 20-30 working days for hemophilia A and 15-25 working days for hemophilia B. Unexpected situations may also occur due to unpredictable objective factors, such as infection due to sampling, miscarriage due to amniotic fluid or chorionic villi extraction, or the occurrence of false positives or false negatives due to sample contamination and prolonged reporting time due to various reasons. Therefore, for those who need prenatal diagnosis, it is recommended to have genetic diagnosis before or at the beginning of pregnancy.