This page gives a general introduction to some prenatal diagnostic techniques available at different stages of pregnancy. Some tests measure abnormal protein levels (Alpha-Fetoprotein test), other tests rely on genetic analysis of fetal/placental cells (Amniocentesis/Chorionic Villus Sampling) and still others rely on measuring known parameters of the embryo/fetus/placenta (Ultrasound). Below can also be found a modified version of an information pamphlet "Checking Your Baby's Health Before Birth".
Ultrasound of 12 week Fetus
Note that the development of in vitro fertilization techniques now allows cells from early stage blastocysts to be removed and genetically analysed prior to implantation. This has raised some ethical issues relating to what parameters will be in future used in blastocyst selection. See also notes on Ultrasound.
There are additional prenatal diagnostic tests under development based upon new molecular techniques such as Quantitative Fluorescent Polymerase Chain Reaction (QF-PCR), Comparative Genomic Hybridization and fetal cells from maternal blood.
There is a separate page for Neonatal Screening
Page Links: Introduction | Some Recent Findings | Information Pamphlet | Ultrasound | Chorionic Villus Sampling (CVS) | Amniocentesis | Coelocentesis | Magnetic Resonance Imaging | Gene Tests | Ethics of Testing | Comparative Genomic Hybridization | NHMRC Recommendations | WWW Links
Other Page Links: Alpha-Fetoprotein (AFP) test | pregnancy-associated plasma protein-A (PAPP-A) | Genetic Abnormalities | Trisomy 21 (Down Syndrome) | Trisomy 18 (Edwards Syndrome) | Ultrasound
Genetic Testing Franssen MT, Korevaar JC, van der Veen F, Leschot NJ, Bossuyt PM, Goddijn M. Reproductive outcome after chromosome analysis in couples with two or more miscarriages: case-control study. BMJ. 2006 Apr 1;332(7544):759-63. "Couples whose carrier status was ascertained after two or more miscarriages have a low risk of viable offspring with unbalanced chromosomal abnormalities. Their chances of having a healthy child are as high as non-carrier couples, despite a higher risk of miscarriage."
Check E. Fetal genetic testing: Screen test. Nature. 2005 Dec 8;438(7069):733-4.)
Ultrasound Ruano R. Recent advances in sonographic imaging of fetal thoracic structures. Expert Rev Med Devices. 2005 Mar;2(2):217-22. "Recent ultrasonographic methods applied in the evaluation of fetal thoracic structures and anomalies are presented."
Below is a modified version of the NSW State Health Publication Checking your baby's health before birth (a similar online resource is available from South Australia). This pamphlet is an example of the information made available to the general public on the diagnostic testing using Ultrasound, Chorionic Villus Sampling (CVS), Amniocentesis, that can be carried out to check the genetic/physical status of the fetus. The original NSW State Health Publication pamphlet has been modified in layout to fit web format and has additional links to UNSW Embryology resources.
Every couple wants to have a healthy baby. For most couples, that will come true. However, there are some couples who have a greater chance than others of having a baby with a birth defect.
Special tests are available which are carried out during pregnancy to determine if the baby has a particular problem. These tests are generally referred to as prenatal diagnosis.
No. Although prenatal diagnosis is highly accurate, a normal test result cannot show up every possible problem with the baby.
There is an increasing number of tests available to detect birth defects. Ask your doctor or genetic counsellor.
The ultrasound scan is a picture of the baby in the uterus (womb). The doctor rubs a jellylike substance on the mother's abdomen before pressing an instrument like a microphone against her skin. Sound waves pass through this instrument into the uterus, through the amniotic fluid and bounce harmlessly off the baby. A computer changes these sound waves into a picture on a television screen so that the outline of the baby is clearly seen.
The ultrasound scan tells your doctor the age of the pregnancy and if you are carrying more than one baby. It can also be used to detect certain things wrong with the baby. This test is harmless to the mother and the baby.
(More? Ultrasound Movies)
This test must be done in the 10th to 12th week after the first day of the mother's last menstrual period. Thus, it is important to see your doctor as soon as you realise that you are pregnant.
The test is done by looking at cells taken from the placenta. No anaesthetic is required, and a test result is usually available in two to three weeks.
When the test is carried out by an obstetrician experienced in the technique, the risk of miscarriage related to the test is about 2 per cent (occurring in 1 in 50 pregnancies).
(More? Prenatal Diagnosis - Chorionic Villus Sampling (CVS))
This test is done in the 14th to 18th week of pregnancy. A small amount of the amniotic fluid is taken from the uterus and then sent to a laboratory to be studied. Cells from the developing baby are found in the amniotic fluid.
No anaesthetic is required, and a result is usually obtained in about three to four weeks. When the test is carried out by an obstetrician experienced in the technique, the risk of a miscarriage related to the test is about 1 per cent (occurring in 1 in 100 pregnancies).
Is a technique of sampling of extracoelomic fluid usually for an early prenatal diagnostic technique.
Magnetic Resonance Imaging (MRI) can be used in fetuses at 18 weeks gestational age or later and has been used mainly in brain and spinal diagnosis. (More? Prenatal Diagnosis - Magnetic Resonance Imaging)
References:
Griffiths PD, Paley MN, Widjaja E, Taylor C, Whitby EH. In utero magnetic resonance imaging for brain and spinal abnormalities in fetuses. BMJ. 2005 Sep 10;331(7516):562-5.
Kok RD, de Vries MM, Heerschap A, van den Berg PP. Absence of harmful effects of magnetic resonance exposure at 1.5 T in utero during the third trimester of pregnancy: a follow-up study. Magn Reson Imaging. 2004 Jul;22(6):851-4.
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.
Links: GeneTests |
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 in Huntington's disease
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."
References:
Clarke A. The genetic testing of children. Working Party of the Clinical Genetics Society (UK) J Med Genet. 1994 Oct;31(10):785-97.
No authors listed Points to consider: ethical, legal, and psychosocial implications of genetic testing in children and adolescents. American Society of Human Genetics Board of Directors, American College of Medical Genetics Board of Directors. Am J Hum Genet. 1995 Nov;57(5):1233-41.
No authors listed International Huntington Association and the World Federation of Neurology Research Group on Huntington's Chorea. Guidelines for the molecular genetics predictive test in Huntington's disease. J Med Genet. 1994 Jul;31(7):555-9.
BMJ - Prenatal genetic testing for parents who won't terminate
This section is not part of the original pamphlet.
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. (More? Prenatal Diagnosis - Comparative Genomic Hybridization)
Most often, the baby will not have the disorder for which the test was done. In those few cases where the test does show a birth defect, the parents will need to have all the necessary information to help them make a choice about continuing the pregnancy. All aspects should be fully discussed with your doctor.
Genetic counselling will provide current information about the disorder and support during this time. Ask your doctor for a referral or contact your local genetic counselling service for an appointment.
The ideal time to learn about prenatal diagnosis is before a planned pregnancy. In some cases, tests need to be done before a pregnancy to check whether the parents are "carriers" of a disorder which may affect their baby.
Further information can be obtained front the following centres. They specialise in prenatal diagnosis and related genetic counselling (these are the original pamphlet listed centres 1997 which may currently differ)
Camperdown
King George V Hospital
Fetal Medicine Unit
Camperdown NSW 2050
Tel: (02) 9515 8258
Westmead
Westmead Centre
Fetal Medicine Unit
Westmead NSW 2145
Tel: (02) 9633 6800
Randwick
Prince of Wales Children's Hospital
Department of Medical Genetics
Randwick NSW 2031
Tel: (02) 93994591
St Leonards
Royal North Shore Hospital
Fetal Medicine Unit
St Leonards NSW 2065
Tel: (02) 9438 7280
Penrith
Nepean Hospital
Fetal Medicine Unit
Penrith NSW 2750 Tel: (047) 924 2114
Newcastle
John Hunter Hospital
Prenatal Diagnosis Unit
Newcastle NSW 2310
Tel: (049) 921 4694
Genetic Education Program, Tel: (02) 438 7324 (Note: phone numbers in NSW are now 9438 7324)
Written in association with the NSW Genetic Education Program
PO. Box 317, St Leonards, NSW 2065. Tel: (02) 9438 7324.
Checking your baby's health before birth. State Health Publication Number (PA) 94-090
1988 recommendations for neonates be assessed for follow-up care under the following conditions.
(see the NHMRC WWW Page)
Each section of the notes covering early development and specific systems contain references to specific abnormalities (on Page 2 of each notes section). The best source for Australian statistical data is the Australian Institute of Health and Welfare National Perinatal Statistics Unit, UNSW which publishes "Congenital Malformations Australia" every 2 years. Be aware that some congenital abnormalities, by their nature, affect multiple systems. In the USA, the Center for Disease Control (CDC) keeps and publishes relevant statistical information. A very difficult issue in abnormal development are the many different Ethical implications.
This current page is a link to Normal and Abnormal Development and Population Data.
Look at types of Abnormal Development that can occur during development.
Alternatively, look at normal development. Development Notes
For those wanting to see dynamic processes of development (and have a reasonably quick connection) then the Movies pages are good for watching changes occur.
The study of human development has relied extensively on studying the process in other model animals. For those wanting to see the process of development in other species then the other embryos pages are a good start.
Home Page
Embryo stages
Fetal Dev
Dev Notes 1
Dev Notes 2
System Notes
Acknowledgements
Abnormal
Major System Abnormalities
Prenatal Diagnosis
Amniocentesis
Alpha- Fetoprotein
PAPP-A
Chorionic Villus Sampling
Comparative Genomic Hybridization
Magnetic Resonance Imaging
Movies
Audio
Class Notes
Serial Images
K12 Students
Abnormal
Embryology in the News
Histology
Site Map
School of Med Sci
UNSW Medicine
University of NSW
UNSW Cell Biology
NCBI Books
Dev Biol (Gilbert)
How do I find out if everything is OK with my developing baby and what are the tests that doctors carry out?
Prenatal diagnosis is based the various types of tests that can be carried out to inform parents and clinicians. With the rising age of mothers in Australia and new knowledge about family genetic history these tools are useful in helping clinicians check the developing fetus. Note that some tests, like ultrasound, are relatively non-invasive, informative, and carried out in many suburban clinics.
This page has 2 main resources:
The first is a NSW Pamphlet "Checking your baby's health before birth." There is a similar online resource available from South Australia.
The second resource covers diagnosis after birth, this is a 1988 NHMRC Recommendation and is a guide to indicators in the neonate.
Please email Dr Mark Hill if you wish to make a comment about this current project.