Regional Medical Laboratory

Prenatal screening and diagnosis are routinely offered for neural tube defects (NTD), Down syndrome, and trisomy 18 detection. The intent of such screening and diagnosis is to enable pregnant women to make informed decisions regarding the pregnancy and be better prepared in the event of the birth of an affected infant.

These risks can only be calculated for gestational ages between 15–22.9 weeks. The optimal collection time is at 16-18 weeks gestation.

PATIENT DEMOGRAPHIC REQUIREMENTS:

Patient Demographic Form

The below information is required for accurate result interpretation:
• Maternal date of birth:
• Maternal weight:
• Maternal race:
• Maternal insulin-dependant diabetes status:
• History of Neural Tube Defects:
• History of Down Syndrome:
• Number of fetuses:
• Estimated Date of Delivery (EDD):
• Method of EDD determination:US/LMP/PE:

Neural Tube Defects

NTD (anencephaly, open spina bifida, and encephalocele) are a heterogenous group of congenital malformations resulting from a failure of fusion of the neural tube. Anencephaly is almost always fatal at or within a few hours of birth. The survival rate, degree of handicap (surgically correctable to severely disabling), and intelligence of children with spina bifida or encephalocele varies with the location and severity of the lesion and the treatment given. The estimated incidence of neural tube defects (~1 per 1300 live births) ranks second to cardiac abnormalities as a cause of major congenital malformations in the United States.

Down Syndrome

Down syndrome (trisomy 21) is a common autosomal aneuploidy characterized by growth retardation, lack of muscle tone, and moderate to severe mental retardation. Fetal demise occurs in about 31% of cases (as assessed from 10 weeks’ gestation to birth). The estimated incidence of Down syndrome in the United States is 1 per 750 live births.3 The risk of having an affected fetus increases with increasing maternal age.

Trisomy 18

Trisomy 18 (Edwards' syndrome) is a chromosomal aneuploidy characterized by severe mental retardation, congenital heart disease, renal malformations, low set ears, and clenched fists. An unknown number of cases spontaneously abort during the first trimester, and approximately 70% of cases spontaneously abort during the second and third trimesters. Thirty percent of those born with trisomy 18 die within the first month of life and 90% within the first year. The estimated incidence is 1 per 6000 live births, and the incidence increases with advanced maternal age.