Methods of Prenatal Screening and Diagnosis
There are multiple ways of classifying the methods available, including the invasiveness and the time performed.
| Invasiveness | Test | Comments | Time |
| Non-invasive | Fetal Cells in Maternal Blood (FCMB) | Based on enrichment of fetal cells which circulate in maternal blood. Since fetal cells hold all the genetic information of the developing fetus they can be used to perform prenatal diagnosis. | First trimester |
| Non-invasive | Cell-free Fetal DNA in Maternal Blood | Based on DNA of fetal origin circulating in the maternal blood. Testing can potentially identify fetal aneuploidy (available in the United States, beginning 2011) and gender of a fetus as early as six weeks into a pregnancy. Fetal DNA ranges from about 2-10% of the total DNA in maternal blood. | First trimester |
| Non-invasive | Preimplantation Genetic Diagnosis (PGD) | During in vitro fertilization (IVF) procedures, it is possible to sample cells from human embryos prior the implantation. PGD is in itself non-invasive, but IVF usually involves invasive procedures such as transvaginal oocyte retrieval | prior to implantation |
| Non-invasive | External examination | Examination of the woman's uterus from outside the body. | First or second trimester |
| Non-invasive | Ultrasound detection | Commonly dating scans (sometimes known as booking scans) from 7 weeks to confirm pregnancy dates and look for twins. The specialised nuchal scan at 11–13 weeks may be used to identify higher risks of Downs syndrome. Later morphology scans from 18 weeks may check for any abnormal development. | First or second trimester |
| Non-invasive | Fetal heartbeat | Listening to the fetal heartbeat (see stethoscope) | First or second trimester |
| Non-invasive | Non-stress test | Use of cardiotocography during the third trimester to monitor fetal wellbeing | Third trimester |
| Less invasive | Transcervical retrieval of trophoblast cells | Cervical mucus aspiration, cervical swabbing, and cervical or intrauterine lavage can be used to retrieve trophoblast cells for diagnostic purposes, including prenatal genetic analysis. Success rates for retrieving fetal trophoblast cells vary from 40% to 90%. It can be used for fetal sex determination and identify aneuploidies. Antibody markers have proven useful to select trophoblast cells for genetic analysis and to demonstrate that the abundance of recoverable trophoblast cells diminishes in abnormal gestations, such as in ectopic pregnancy or anembryonic gestation. | First trimester |
| Less invasive | Maternal serum screening | Including β-hCG, PAPP-A, alpha fetoprotein, intact or beta hCG, inhibin-A. See separate section below |
First or second trimester |
| More invasive | Chorionic villus sampling | Involves getting a sample of the chorionic villus and testing it. This can be done earlier than amniocentesis, but may have a higher risk of miscarriage, estimated at 1%. | After 10 weeks |
| More invasive | Amniocentesis | This can be done once enough amniotic fluid has developed to sample. Cells from the fetus will be floating in this fluid, and can be separated and tested. Miscarriage risk of amniocentesis is commonly quoted as 0.06% (1:1600). By amniocentesis is also possible to cryopreserve amniotic stem cells. | After 15 weeks |
| More invasive | Embryoscopy and fetoscopy | Though rarely done, these involve putting a probe into a women's uterus to observe (with a video camera), or to sample blood or tissue from the embryo or fetus. | |
| More invasive | Percutaneous umbilical cord blood sampling |
Read more about this topic: Prenatal Diagnosis
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