The purpose of the prenatal hemoglobinopathy screening program is to identify couples whose children may be at high risk to have an inherited hemoglobinopathy (blood disease). The program is targeted to the ethnic groups that have an increased risk for these conditions.
Hemoglobinopathy screening is part of every woman's initial prenatal lab work. If your screening results suggest you might be a carrier of hemoglobin trait, your laboratory results are further evaluated by a program coordinator. If there is the possibility of a significant hemoglobinopathy in your baby, you are referred to one of four Northern California Genetics Centers for further follow-up.
A genetic counselor will contact you and offer hemoglobinopathy screening to the father of the baby to identify his hemoglobin status. If both parents are identified as carriers of a hemoglobin trait, the fetus is at a 25% risk to be affected with a hemoglobinopathy. Depending on the type of hemoglobinopathy, the couple is offered prenatal diagnosis so they can know if the fetus is affected.
Hemoglobinopathy screening can be performed at any time in pregnancy, but it is most useful when done early in pregnancy (between 10-20 weeks). If a pregnancy is affected with a significant hemoglobinopathy, the parents would have the option of either ending the pregnancy, or continuing the pregnancy with time to prepare for a child with the condition. Parents who choose not to have screening are not doing any harm to their unborn child.
If your baby is determined to have a hemoglobinopathy (blood disease), you will be given more information about the specific problem and how it may affect the baby. This may include a discussion with your primary OB provider, a genetic counselor, geneticist, perinatologist or other pediatric specialist. All available treatments and options for continuing or ending the pregnancy are discussed when the problem is identified.
Our blood is made up of millions of red blood cells. The red blood cells contain hemoglobin, which carries oxygen throughout the body. There are many different types of hemoglobin that can be found in the blood. The most common type of hemoglobin in humans is called hemoglobin A. Hemoglobin A is a formed from proteins made by the body called alpha chains and beta chains. Hemoglobin A has two alpha chains (α2) and two beta chains (β2). Another common form of hemoglobin is called hemoglobin A2. This type of hemoglobin is made from two alpha chains and two delta chains, making it different than hemoglobin A. It makes up a much smaller amount of the total hemoglobin found in the body. Generally, it accounts for less than 3% of all the hemoglobin present in the red blood cells. Hemoglobin F is another common hemoglobin, but is found in even smaller amounts than hemoglobin A2. It is made of two alpha chains and two gamma chains. Hemoglobin F is the main hemoglobin during fetal development. After birth, hemoglobin F decreases slowly and eventually accounts for less than 2% of the total hemoglobin. Most people have just these three hemoglobin types in their blood.
Sometimes, a change in the proteins that make hemoglobin results in a different hemoglobin type than the usual three. When the change affects the way hemoglobin forms, it is called a hemoglobin variant. There are over 500 different types or variations of hemoglobin found all over the world. Most often these variants are caused by a genetic mutation in the instructions for the beta chains, but they can affect any of the proteins that make hemoglobin. Many variants have no effect on the way hemoglobin works.
Sometimes the body makes less of one of the protein chains that form hemoglobin. When this happens, the body can still make the usual three hemoglobins (A, A2 and F), but the red blood cells are usually smaller. This type of change is called "thalassemia".
All the information about how hemoglobin is made is inherited from your parents. Each parent provides instructions for every protein that makes hemoglobin (alpha chains, beta chains, etc). A change in the genetic instructions that affects the way hemoglobin forms or the amount being made, it is referred to as a hemoglobin trait. Hemoglobin traits rarely cause health problems. Some people who carry hemoglobin traits may express very minor signs such as mild anemia or small red blood cells. Most people are completely unaware that they carry a hemoglobin trait unless special testing is ordered. Like other inherited traits, hemoglobin traits may be passed along for many generations.
A person who inherits a hemoglobin trait from both parents has a hemoglobinopathy (inherited blood disease). This only happens when both parents have the same (or similar) hemoglobin trait. The medical problems caused by inherited blood diseases are extremely variable. Some blood diseases result in prenatal or infant death. Other blood diseases cause chronic medical problems and require regular medical care. There are some blood diseases that are relatively mild and have few, if any medical problems. The kind of problems that may happen depend on the specific hemoglobinopathy.
Hemoglobins traits are found in people worldwide. They are more common in regions of the world where malaria is frequent. It is believed that hemoglobin traits partially protect the carrier against malaria infection.
Sickle cell anemia is a worldwide health problem with occurrences in Africa, South America, Latin America, the West Indies, Greece, Spain, Italy, and Turkey; and in people who live around the Mediterranean Sea. In the United States, one out of every 10 African-Americans has sickle cell trait, and one out of every 400 African-Americans has sickle cell anemia.
Thalassemia traits are found in people whose ancestors come from Cyprus, Greece, Italy, Turkey, the Arabian Peninsula, and Asia, including India, Pakistan, Southern China, Thailand, Cambodia, Vietnam and Laos. It is also found in people from Africa and the West Indies. It is estimated that two million people in the United States have thalassemia trait.
A hemoglobinopathy screen usually starts with a complete blood count (CBC). This is done as part of routine prenatal testing. Additional tests, including hemoglobin electrophoresis (Hgb E4) and iron studies (ferritin), are automatically done when the CBC shows small red blood cells or if you request ethnicity-based genetic screening. These laboratory tests are used by the prenatal hemoglobinopathy screening program to identify pregnant women who carry hemoglobin traits. Almost all hemoglobin traits can be identified using these laboratory tests.
DNA testing can help identify the specific genetic change (mutation) that causes a hemoglobin trait or disease.
Almost all hemoglobinopathies are inherited in an autosomal recessive manner. With each pregnancy, parents who both have a hemoglobin trait have a 25% chance of having a child with a hemoglobinopathy. There is also a 50% chance of having a healthy child with a hemoglobin trait and a 25% chance of having a healthy child without any hemoglobin trait. These risks apply to each pregnancy.