How are neural tube defects diagnosed?
At birth, the diagnosis of a neural tube defect is usually obvious based on external findings. Prenatal diagnosis may be made with ultrasound examination after 12-14 weeks of pregnancy. Screening of pregnancies can be carried out at 16 weeks by testing the mother's blood for the level of alpha-fetoprotein. Open neural tube defects leak this fetal chemical into the surrounding amniotic fluid, a small portion of which is absorbed into the mother's blood. During an MSAFP profile, a small amount of blood is taken from your arm and measured for three chemicals (alpha-fetoprotein, estriol, and human chorionic gonadotropin). If the level of these chemicals is higher than normal, it may mean that your baby has a neural tube defect. However, it can also mean that your fetus is older than expected, or that you are carrying more than one fetus. Your doctor will offer additional tests (like an ultrasound or an amniocentesis) to evaluate the health of your baby.