Genetic screening is done for a particular condition in individuals, groups or populations without family history of the condition Genetic testing is done for a particular condition where an individual is suspected of being at increased risk due to their family history or the result of a genetic screening test. No. On its own, the blood test cannot definitely identify any birth defect. It can tell the woman and her doctor that there may be a greater possibility than average that the baby has a particular birth defect such as a chromosomal problem or a neural tube defect such as spina bifida. As the ultrasound scan used to measure the nuchal translucency is done early in the pregnancy, it is usually recommended that another ultrasound scan be done at 18 to 20 weeks to look carefully at the baby?s physical development.