Prenatal diagnosis and prenatal screening are aspects of prenatal care that focus on detecting anatomic and physiologic problems with the zygote, embryo, or fetus as early as possible, either before gestation even starts (as in preimplantation genetic diagnosis) or as early in gestation as practicable.
They use medical tests to detect problems such as neural tube defects, chromosome abnormalities, and gene mutations that would lead to genetic disorders and birth defects, such as spina bifida, cleft palate, Tay–Sachs disease, sickle cell anemia, thalassemia, cystic fibrosis, muscular dystrophy, and fragile X syndrome.
It is worth to note that this test is not done at all times of the pregnancy.
This is because the accuracy and the effectiveness of the test will majorly depend on the stage of the pregnancy.
No single serum β-HCG level is diagnostic of an ectopic pregnancy.
Serial serum β-HCG levels are necessary to differentiate between normal and abnormal pregnancies and to monitor resolution of ectopic pregnancy once therapy has been initiated.
This is the period that the embryo is transformed into a fetus.