Читать книгу Protocols for High-Risk Pregnancies - Группа авторов - Страница 139

Patients at risk of being a carrier or being affected by a hemoglobinopathy should be screened appropriately in order to assess fetal and maternal risks in pregnancy. The American College of Obstetricians and Gynecologists currently does not support universal hemoglobinopathy screening.

At‐risk groups for hemoglobinopathies include high‐risk ethnic groups and patients with unexplained microcytic anemia. Persons of African, Mediterranean, Southeast Asian, Middle Eastern, and West Indian descent should be considered high risk. Initial screening should include a hemoglobin electrophoresis. Sickle cell solubility tests are not an adequate initial screen as they will not differentiate SCD from sickle cell trait, and they can miss compound heterozygotes.

Hemoglobin electrophoresis results will vary with the disease state present. Normal hemoglobin electrophoresis results show 95–98% HbA, 2–3% HbA2, and 0.8–2% HbF. Sickle cell disease, sickle cell trait, and beta‐thalassemia syndromes will be diagnosed on electrophoresis. Alpha‐thalassemia cannot be diagnosed by electrophoresis and instead requires genetic testing.

For patients with a microcytic anemia on routine laboratory testing, additional testing is warranted. The majority of cases of microcytic anemia are due to iron deficiency anemia; however, among patients in whom iron deficiency has been ruled out and who have a normal hemoglobin electrophoresis, genetic testing for alpha‐thalassemia trait should be completed.

If the patient is noted to be affected or a heterozygous carrier, paternal testing should be completed to determine fetal risks. Pregnancies at risk of an affected fetus (including pregnancies where both parents are carriers or where one parent is a carrier and one parent is affected) should be referred for genetic counseling for full assessment of inheritance risk and discussion of prenatal testing options including fetal diagnostic testing through chorionic villus sampling and amniocentesis depending on gestational age. Noninvasive prenatal tests for cell‐free DNA in maternal circulation are in development but currently there are no validated tests for hemoglobinopathy. In patients presenting for preconception counseling with a known risk for conceiving an affected fetus, preimplantation genetics and in vitro fertilization is an option.