Micah Anthony Short | home
Anencephaly is a birth defect that occurs when the bones of the skull do not close properly. It is a type of "open neural tube defect" (ONTD). Anencephaly is a serious problem and babies with anencephaly will not survive.
Anencephaly occurs between the third and fourth week of fetal (before-birth) development. The brain and spinal cord first form as a flat strip of cells. Then, the sides of this strip curl up and "zip" together to form a tube, called the "neural tube". In the case of anencephaly, however, the portion of the tube that forms the brain does not close completely. This results in an opening of the skull.
Babies with anencephaly can survive inside the womb because their vital organs, such as heart and kidneys, are normal and they receive nutrients from the mother's blood. Unfortunately, however, there is no way to correct the open part of the brain, which is needed for survival. Therefore, in most cases, the baby is either stillborn or dies shortly after birth.
Most babies with anencephaly look normal except for the opening on the head.
No one knows for sure what causes anencephaly or the other type of ONTD, spina bifida (opening along the backbone). However, a combination of genetic and environmental factors is believed to be involved.
It is very important to understand that an ONTD is not a result of anything that the mother did (or did not do) during her pregnancy. Anyone can have a baby with an ONTD. Unless we have a family history of ONTD's we may not know that we have the genetic tendency.
Also, no one knows exactly what environmental factors may play a role in the occurrence of ONTD's. ONTD's occur more often when mothers have too little folic acid in the diet. However, anencephaly or spina bifida can also occur when the mother does have enough folic acid in the diet, either from foods such as fortified breakfast cereals, orange juice, liver, asparagus, and broccoli, and/or from taking prenatal vitamins or over-the-counter vitamins that include folic acid in recommended doses.
Anencephaly or spina bifida occurs in about 1 to 2 per 1,000 births in the Caucasian population and in about 1 in 2,000 births in the African-American population. Geographically, ONTD's occur more frequently in the eastern United States than on the West Coast and in urban areas more often than rural areas. Risks are also increased if a close family relative has had a baby with an ONTD.
Because genes are involved in ONTD's, parents who have had one child with anencephaly or spina bifida have about a 4% chance of having another child with an ONTD. The risk increases to 10% for parents who have had two children with an ONTD. Brothers and sisters of an affected individual have about a 1% chance, aunts and uncles have about a 0.5% to 1% chance of having a child with an ONTD. The risk of having a child with an ONTD gets lower as the blood relationship to the affected baby gets weaker.
The risk of having another baby with an ONTD may possibly be reduced. Some researchers have reported that mothers who take folic acid supplements after having one baby with an ONTD have less chance of having another. For mothers who have had one child with an ONTD and who plan to have another child, the recommended daily allowance (RDA) for folic acid is 4 mg (10 times the usual RDA of 0.4 mg) both before pregnancy and during the first six weeks of pregnancy.
There are certain tests that can be performed in order to detect an ONTD early on.
- this is the most accurate way to detect an ONTD. This is performed by testing samples of amniotic fluid, this test is about 98% effective in determining an ONTD. This test is performed between 15 and 22 weeks of pregnancy. Tests to detect ONTD's include measuring the levels of two chemicals, alpha-fetoprotein (AFP) and acetyl cholinesterase (AChE).
is a protein produced by the baby and excreted in the baby's urine, which is in the amniotic fluid. Any opening along the baby's body may result in more AFP in the amniotic fluid.
, which should be enclosed in the spinal column, is not normally found in the amniotic fluid.
If the baby has an ONTD, AChE may be detected and the AFP level may be high.
In addition to tests to detect ONTD's, amniotic fluid is usually tested to detect chromosome problems. Chromosomes contain our genetic material called genes. A set of chromosomes - normally 46 - is contained in each cell of the body. Having too many or too few chromosomes usually leads to physical abnormalities that cause some degree of mental retardation and health problems.
Maternal Serum Alpha-fetoprotein (MSAFP) Triple Screen-
this test also detects AFP and is performed by testing samples of the mother's blood. However, this test is not as accurate as amniocentesis and is not recommended for couples with a higher risk of having a child with an ONTD.
(also known as a sonogram) is usually performed during the second trimester of pregnancy. This test uses high-frequency sound waves to produce a black-and-white picture of the baby. By examining the picture, doctors can detect most cases of anencephaly and many (but not all) cases of spina bifida.
According to current laws, the only organs that can be donated from a baby with anencephaly are heart valves.
The information used on this page was obtained from Patient Education - Anencephaly, literature supplied by The Western Pennsylvania Hospital.