prenatal diagnosis Flashcards
basic principles of prenatal screening
- Screen the General Population for Common Disorders - Down syndrome, birth defects. 2. Offer Screening to at Risk Groups for Clustered Disorders- Cystic fibrosis, Tay Sachs. 3. Offer Screening to Families with Known Disorders
Indications for Ultrasound
Fetal presentation, Suspected multiple gestation, Establish EDD, Suspected fetal death, Suspected oligohydraminos, Abnormal AFP , fetal anatomy, placenta location
Fetal presentation, Suspected multiple gestation, Establish EDD, Suspected fetal death, Suspected oligohydraminos, Abnormal AFP , fetal anatomy, placenta location
How is gestational age estimated in first trimester
Crown-rump length on US- can only be used early because later on the fetus extends and flexes its spine
How is gestational age estimated in 2-3 trimester
Biparietal diameter, abdominal circumference, femur length on US
screening for trisomies and neural tube defects
Check maternal serum for alpha-feto protein, unconjugated estriol, HcG and inhibin A. On US look for nuchal translucency
list the non-invasive vs invasive testing methods
non invasive: maternal serum for analytes (ie. AFP), karyotype, fetal cells. Also ultrasound. Invasive: amniocentesis or chorionic villus sampling, both have small risk to fetus.
indications for invasive diagnostic methods
Advanced maternal age (defined as > 35 years old at due date), Positive aneuploidy screening test (biochemical and/or ultrasound), Abnormal ultrasound findings: anatomic, IUGR, amniotic fluid volume, Known parental chromosome rearrangements, Previous affected child
Where is alpha feto protein made
fetal yolk sac and liver
What is alpha feto protein
major blood protein of fetus- like albumin. It is not present in maternal blood normally, so any AFP is from the fetus.
Causes of high and low alpha feto protein
high: neural tube defects (the defect causes release of more AFP into the amniotic fluid), omphalocele (abd defect), gastroschisis (abd defect). Low: downs syndrome
list conditions which Ashkenazi Jews are at increased risk for
AR conditions- Tay Sachs, Canavan disease, Gaucher disease, Nieman-Pick disease, Bloom syndrome, Fanconi anemia C, and mucolipidosis
What is Tay Sachs
AR lysosomal storage disorder caused by a deficiency in hexosaminidase A. Gangliosides accumulate in the body, and their presence in the CNS leads to blindness, severe neurologic disease, and death, usually by the age of 6
Diagnosis of fetal Tay Sachs
Molecular DNA testing detects 94 % of heterozygotes, while the analysis of the ratio of hexosaminidase A to total hexosaminidase detects 98 %. In at risk pregnancies, fetal DNA can be evaluated from samples obtained via amniocentesis or CVS
Diagnosis of hemoglobinopathies
Thalassemias: MCV <80% followed by hemoglobin electrophoresis once iron deficiency is excluded
Cystic fibrosis diagnosis
Prenatally or newborn. Prenatal testing of CF gene . 75% have delta F508 deletion. Panels are available to test for less common mutations, but not all mutations are known so some may be missed. Start by testing mom, then offer partner testig if mom is positive. If both are affected, CVS or amniocentesis is offered.
