This current page is a general starting point for the topic of prenatal diagnosis, the links below are to resources that give more specific information about some diagnostic techniques available at different stages of pregnancy. The two major classes of techniques are invasive and non-invasive testing and the results of these tests most commonly show normal development. When abnormal development is identified this can be due to genetic, environmental, unknown causes or a combination of these effects. (More? Abnormal Development) A trend in developed countries of an increasing maternal age, long associated with increased genetic abnormalities, has emphasised the need for good diagnostic low risk tests that allow informed decisions early in a pregnancy. (More? Genetic) In contrast, in developing countries environmental effects such as infections and nutrition can impact upon embryonic and fetal development (More? Environmental | Nutrition)
Recently with the growth in Assisted Reproductive Technologies (ART) or commonly known as In Vitro Fertilization (IVF), there is a new "form" of prenatal diagnosis that involves genetic testing of the blastocyst before implantation. (More? Assisted Reproductive Technology)
There are other pages that refer to postnatal diagnostic testing. (More? Neonatal Diagnosis)
- This Embryology site is a developmental educational resource, it does not provide specific clinical details, you should always refer to a health professional.
- Diagnosis Links: Prenatal Diagnosis | Pregnancy Test | Amniocentesis | Chorionic villus sampling | Ultrasound | Alpha-Fetoprotein | Pregnancy-associated plasma protein-A | Fetal Blood Sampling | Magnetic Resonance Imaging | Computed Tomography | Preimplantation Genetic Screening | Comparative Genomic Hybridization | Neonatal Diagnosis | Category:Prenatal Diagnosis | Fetal Surgery | Category:Neonatal Diagnosis | Assisted Reproductive Technology | In Vitro Fertilization | Journal - Prenatal diagnosis
|Amniocentesis||Chorionic villus sampling||Ultrasound|
Some Recent Findings
Percutaneous umbilical blood sampling (PUBS, fetal blood sampling, umbilical vein sampling) This chromosome analysis test is done at in the 18th week or later of high-risk pregnancies. The technique may be used when either alternative tests (amniocentesis, CVS, ultrasound) are either inconclusive or not achievable (severe oligohydramnios).
The risk of a miscarriage related to the test is about 3 per cent (occurring in 3 in 100 pregnancies).
Is a technique of sampling of extracoelomic fluid usually for an early prenatal diagnostic technique.
As a prenatal diagnostic test, a positive fetal fibronectin test result can indicate a higher risk of preterm delivery, but may also has false positive results. The negative result is more reliable as an indicator of reduced risk of preterm birth.
(fFN) is an extracellular matrix glycoprotein produced by fetal cells. Fetal fibronectin appears to act as an adhesive between the interface of the chorion and the decidua (fetal membrane and uterine lining).
There are clinically more and more tests becoming available as we learn more about the genetic basis of some diseases. The most common diagnostic test relates to the current trend in an increasing maternal age, which has long been associated with an increase in genetic abnormalities, the most frequent of these is trisomy 21 or Down syndrome.
A recent publication from NHMRC Medical Genetic Testing: information for health professionals (2010). This paper covers background information on all types of genetic tests, not just those associated with prenatal diagnosis.
Types of genetic tests
- Somatic cell genetic testing involves testing tissue (usually cancer) for non-heritable mutations. This may be for diagnostic purposes, or to assist in selecting treatment for a known cancer.
- Diagnostic testing for heritable mutations involves testing an affected person to identify the underlying mutation(s) responsible for the disease. This typically involves testing one or more genes for a heritable mutation.
- Predictive testing for heritable mutations involves testing an unaffected person for a germline mutation identified in genetic relatives. The risk of disease will vary according to the gene, the mutation and the family history.
- Carrier testing for heritable mutations involves testing for the presence of a mutation that does not place the person at increased risk of developing the disease, but does increase the risk of having an affected child developing the disease.
- Pharmacogenetic testing for a genetic variant that alters the way a drug is metabolised. These variants can involve somatic cells or germline changes. Even if these variants are heritable (that is germline changes), the tests are usually of relevance to genetic relatives only if they are being treated with the same type of medication.
A new site developed by NIH "GeneTests" provides medical genetics information resources available at no cost to all interested persons. It contains educational information, a directory of genetic testing laboratories and links to other databases such as OMIM.
Comparative Genomic Hybridization
This new test under development is based upon microarray-based comparative genomic hybridization (array CGH).
All fetal cells should have complete copies of maternal and paternal genomes. The test compares regions of fetal DNA that deviate from this "pattern" due to either too much or too little DNA, alterations reflect regions of the genome that are either copied or deleted. These genetic changes may therefore cause disease.
Ethics of Testing
Major developmental abnormalities detected early enough can be resolved far more easily than those discovered late in a pregnancy.
What are the ethical questions that are raised by prenatal testing? Future individual rights or parents rights? But what about diseases, like Huntington's, where a diagnostic test can be made but there are no current treatments for the postnatal (95% of cases adult onset) disease?
Guidelines for the molecular genetics predictive test
- Recommendation 2.1 "the test is available only to individuals who have reached the age of majority."
- Recommendation 7.2 "the couple requesting antenatal testing must be clearly informed that if they intend to complete the pregnancy if the fetus is a carrier of the gene defect, there is no valid reason for performing the test."
- ↑ Xin Guo, Philip Bayliss, Marian Damewood, John Varney, Emily Ma, Brett Vallecillo, Ravinder Dhallan A noninvasive test to determine paternity in pregnancy. N. Engl. J. Med.: 2012, 366(18);1743-5 PMID:22551147
Robert Liston, Diane Sawchuck, David Young, Society of Obstetrics and Gynaecologists of Canada, British Columbia Perinatal Health Program Fetal health surveillance: antepartum and intrapartum consensus guideline. J Obstet Gynaecol Can: 2007, 29(9 Suppl 4);S3-56 PMID:17845745
November 2010 "Prenatal Diagnosis" All (63715) Review (8631) Free Full Text (6349)
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Prenatal Diagnosis Terms
- false negative rate - The proportion of pregnancies that will test negative given that the congenital anomaly is present.
- false positive rate - The proportion of pregnancies that will test positive given that the congenital anomaly is absent.
- negative predictive value - The probability that a congenital anomaly is absent given that the prenatal screening test is negative.
- positive predictive value - The probability that a congenital anomaly is present given that the prenatal screening test is positive.
- pre-implantation genetic diagnosis - (PGD) a screening procedure for embryos produced through in vitro fertilisation (IVF) for genetic diseases that would generate developmental abnormalities or serious postnatal diseases.
- prenatal screening sensitivity - (detection rate) The probability of testing positive on a prenatal screening test if the congenital anomaly is present.
- prenatal screening specificity - The probability of testing negative on a prenatal screening test if the congenital anomaly is absent.
External Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name.
- Australian and New Zealand - College of Obstetricians and Gynaecologists Intrapartum Fetal Surveillance Clinical Guidelines - Second Edition (June 2011)
- Canada - Society of Obstetricians and Gynaecologists of Canada