Spina Bifida
Description of disorder:
Spina bifida is a term that is used to describe a series of birth defects that affect the development of the spine and central nervous system. The central nervous system is made up of the brain, nerves and spinal cord. The spinal cord runs from the brain to the rest of the body and consists of nerve cells and bundles of nerves that connect all parts of the body to the brain.
There are different types of Spina Bifida, including Spina Bifida Occulta,
Spina Bifida Meningocele and Myelomeningocele. Myelomeningocele is the most serious type of Spina Bifida and effects roughly one in 1000 babies that are born in Britain. are born in Britain.
In Myelomeningocele, the spinal column remains open along several vertebrae (the disc-shaped bones that make up the spine). The membranes and spinal cord push out to create a sac in the baby’s back. Sometimes the sac is covered with membranes called meninges, although it often remains open, leaving the nervous system vulnerable to infections that may be fatal.


Scientific basis (what is the test is looking for)
A common test used to check for myelomeningocele is the maternal serum alpha-fetoprotein (MSAFP) test. To perform this test, your doctor draws a blood sample and sends it to a laboratory, where it's tested for alpha-fetoprotein (AFP) — a protein that's produced by the baby. It's normal for a small amount of AFP to cross the placenta and enter the mother's bloodstream, but abnormally high levels of AFP suggest that the baby has a neural tube defect, most commonly spina bifida or anencephaly, a condition characterized by an underdeveloped brain and an incomplete skull. (Mayoclinic, Oct 2011)
A ultrasound can be carried out to look for the sac or cyst (like a blister) on the back, covered by a thin layer of skin. The sac contains tissues that cover the spinal cord, cerebrospinal fluid and sometimes even the nerves and tissues of the spinal cord itself. (BBC Health[online])
If a blood test shows high levels of AFP in your blood but the ultrasound is normal, your doctor may offer amniocentesis. During amniocentesis, your doctor uses a needle to remove a sample of fluid from the amniotic sac that surrounds the baby. An analysis indicates the level of AFP present in the amniotic fluid.
A small amount of AFP is expected in amniotic fluid. However, when an open neural tube defect is present, the amniotic fluid contains an higher than expected amount of AFP because the skin surrounding the baby's spine is gone and AFP leaks into the amniotic sac. (Mayoclinic, Oct 2011)

A positive test =
A positive test result for Spina Bifida would mean that higher than usual AFP results have been detected by the blood test and have either been confirmed by the amniocentesis, or other visible signs of Spina Bifida being shown by an ultrasound, which therefore means it is likely or certain that the infant will be born with Spina Bifida.

A negative test =
A negative test for Spina Bifida would mean that small or trace amounts of AFP were found in the blood; the normal amount for a pregnant woman to have, and the baby had no visible signs of Spina Bifida, such as the sac on the back, being detected by the ultrasound, which therefore means that there is a very low chance of the infant being born with Spina Bifida.

Rhesus Factor
Description:
Each of the four blood types is additionally classified according to the presence of another protein on the surface of RBCs that indicates the Rh factor. If you carry this protein, you are Rh positive. If you don't carry the protein, you are Rh negative.
Most people — about 85% — are Rh positive. But if a woman who is Rh negative and a man who is Rh positive conceive a baby, there is the potential for a baby to have a health problem. The baby growing inside the Rh-negative mother may have Rh-positive blood, inherited from the father. Approximately half of the children born to an Rh-negative mother and Rh-positive father will be Rh positive. (Steven Dowshen, kidshealth.org[online], December 2008)
Problems can arise if an Rh-negative mom-to-be carries an Rh-positive baby. The mother's body may mistake the baby's blood cells as intruders and start making antibodies to attack them


Scientific basis (what is the test is looking for)
The Rh factor is a protein carried by red blood cells in some people, and not in others. If you have the protein, you are Rh positive. If not, you are Rh negative. A blood test can determine this, and which one you are. A blood test can diagnose both the RH factor of the mother and the baby to see if they match or if they conflict. Rh testing is usually done during a woman's first blood test during pregnancy. RhoGAM injections for Rh-negative women are given at 28 or 29 weeks and again within 72 hours of delivery. The RhoGAM injection is also administered after any genetic testing that could result in mixing of maternal and fetal blood, such as CVS (chorionic villus sampling) or amniocentesis. (whattoexpect.com/pregnancy[online])

A positive test =
A positive test for Rhesus Factor would mean that the baby and the mother's RH factor was not the same, (one was positive and one was negative) and therefore there would be a chance of the mother's antibodies attacking the foetus.

A negative test =
A negative test for Rhesus Factor would show that the mother and infant's RH Factor was the same, either both positive or both negative, therefore meaning a smooth and normal pregnancy.