The psychiatric patient: a challenge for a TIS service

Abstract

This chapter describes the prenatal diagnosis of open neural tube defects (NTD). Spina bifida and anencephaly, which collectively account for nearly all NTD, are serious fetal malformations resulting from incomplete closure of the neural tube during embryogenesis. The two occur in approximately a 1:1 ratio, and roughly 20% of spina bifida lesions are skin-covered. Mean alpha-fetoprotein (AFP) concentrations in amniotic fluid fall steadily throughout the second trimester, emphasizing the need to document gestational age before interpreting test results. AFP is the major fetal serum protein during the early weeks of pregnancy, occurring in concentrations as high as 300 mg/100 ml at the twelfth week of gestation. It is found that about 40% of anencephalic and 20% of open spina bifida pregnancies are associated with bloodstaining. Brown samples also appear on occasion. These latter rarely have intact red cells but may have detectable hemoglobin F. Rather than being procedure-related, these brown samples are felt to indicate an earlier spontaneous hemorrhage. A report indicates that identification of a specific molecular form of acetylcholinesterase (AChE) in amniotic fluid can be useful both in diagnosing neural tube defects and in identifying false-positive AFP results.