Along with considering the "critical periods" of development, think also about the organ systems that continue to develop either into the late fetal period (respiratory, genitalia), change at birth (respiratory, cardiovascular) or continue developing postnatally (neural, respiratory).
Image Source: http://www.people.virginia.edu/~rjh9u/hdevsum.html
A generalized overview of periods when development of organ systems are most sensitive to disruption causing major congenital anomalies (dark blue bars) and periods which may cause minor anomalies (light blue bars).
Note that the embryonic stage (first trimester) is more vulnerable than the fetal period (second and third trimesters).
This graph should help you think about the effects of maternal lifestyle and/or teratogens on Embryonic/Fetal development.
Which systems are the most sensitive to disruption, when and why?
Abnormal development (covered in detail UNSW Embryo- Abnormal Dev) is generally divided into either Congenital (inherited or genetic) or Maternal derived abnormalities. There can also be an interaction between the 2 types, with teratogen impact dependent on the genetic background of mother/fetus.
Embryos with major genetic abnormalities, that impact on developmental processes, in general fail to develop and are spontaneously aborted. In other embryos, there are several known genetic abnormalities (on the basis of maternal age or family history) that can now be screened for with prenatal testing (More? Genetic Abnormalities).
Many genetic developmental abnormalities involve only small DNA mutations affecting individual or a few genes, exceptions to tthis are those that involve abnormal segregation of chromosomes giving an abnormal chromosome complement to the developing embryo. is Down syndrome (or trisomy 21) and then Edwards syndrome (trisomy 18, there is also less commonly trisomy 9, 13, 15). Note that the occurance of chromosomal abnormalities also increases with increasing maternal age.
There are several pamphlets providing information about prenatal diagnosis (NSW State Health Publication Checking your baby's health before birth).
Environmental abnormalities (often called maternal derived abnormalities) relate to lifestyle, infection, maternal health and nutrition.
Infections, collectively grouped under the acronym TORCH for Toxoplasmosis, Other organisms (parvovirus, HIV, Epstein-Barr, herpes 6 and 8, varicella, syphilis, enterovirus) , Rubella, Cytomegalovirus and Hepatitis. (See also a page on bacterial infections and viral infections) The developmental outcome is not always clear as effects can depend on the genetic background of the fetus, time (critical period) and severity of infection and other variables. For example, some viruses cross the placenta and can directly infect the fetus (reliant on passive immunity from the mother) with impact of different systems. The viral infection can also cause fever in the mother, with increased temperature (hyperthermia) having indirect effects on embryonic/fetal development.
Maternal drugs effects either alcohol (fetal alcohol syndrome), smoking, prescription drugs (therapeutic chemicals/agents, thalidomide limb development), non-prescription drugs (smoking), and illegal drugs (Cannabis/Marijuana, Methamphetamine/Amphetamine, Cocaine, Heroin, Lysergic Acid Diethylamide)
Environment, for example smoking, chemical, heavy metals and even maternal endocrine function (maternal diabetes, thyroid development).
In addition to these obvious environmentally derived abnormalities, there is growing evidence that the interuterine environment has a strong influence on later postnatal health and neurological development. This theory is based on the early statistical analysis of disease/longevity in babies with low birth weights in England by Barker, and was initially called the "Barker Hypothesis" and now called the Fetal Origins Hypothesis.
Maternal Nutrition, for example directly as shown by inadequate dietry folate intake (neural tube defects) or indirectly by the effects of maternal lifestyle on quality of nutrition (see above).
Maternal Health, for example the increasing incidence of type 2 Diabetes in the population, which can also impact on fetal development (maternal diabetes).
A Teratogen are any agent that causes a structural abnormality following fetal exposure during pregnancy. The overall effect depends on dosage and time of exposure (see above graph).
Absolute risk - the rate of occurrence of an abnormal phenotype among individuals exposed to the agent. (e.g. fetal alcohol syndrome)
Relative risk - the ratio of the rate of the condition among the exposed and the nonexposed. (e.g. smokers risk of having a low birth weight baby compared to non-smokers)
A high relative risk may indicate a low absolute risk if the condition is rare.
University of South Dakota - Teratogens
Oxford University - List of Known and Suspected Teratogens (Source primarily Dangerous Properties of Industrial Materials, 7th Ed., by N. Irving Sax and Richard J. Lewis)
Genetic Drift Online (1995) - Teratogen Update
Yale University - Environmental Causes of Birth Defects (by Sherree L. Kassuba)
Merck Manual Online -
Section 18. Gynecology and Obstetrics |
Section 18, Ch.250, High-Risk Pregnancy
The following questions are designed to make you think about clinical issues associated with this early stage of embryonic development. The answers will not be provided in the Lab and but will be available on the web. You will need internet access to use some of the links in this exercise.
Please note that questions are not directly examinable.
(UNSW Embryology Links are from the Embryology CD also available on the Web)
1. What is chorionic villus sampling (CVS)?
2. What does CVS show and what alternative tests are available?
3. What are the effects of high levels of maternal alcohol on the developing embryo?
4. What other maternal conditions can affect development of the embryo?
5. How are birth defects monitored in Australia?
6. What is OMIM?
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S |T | U | V | W | X | Y | Z
Movie of Human Embryo Growth (this shows a human embryo growing, all images are to scale)
Movie of Limb Growth(this shows development of the human arm from bud to paddle, to hand with arm)
Movie of Mouse Embryo Growth (this shows a mouse embryo growing)
Movie of Rotating Embryo(this shows an early embryo from all angles)
All Moviesthis shows many different ways of looking in at changes in different embryos.
Home Page
Embryo stages
Fetal Dev
Dev Notes 1
Dev Notes 2
System Notes
Acknowledgements
Practical 11
Introduction
Stage 16
Stage 17
Stage 18
Stage 19
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Stage 21
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Stage 23
Fetus Week 10
Fetus
Clinical Considerations
Abnormal
BGDA FAQ
Practical 3
Practical 4
Lecture 5
Lecture 6
Movies
News
Class Notes
Serial Images
K12 Students
Abnormal
Histology
Site Map
School of Med Sci
UNSW Medicine
University of NSW
UNSW Cell Biology
NCBI Books
Dev Biol (Gilbert)
Use the graph on this page and the linked resources to now compare what you have learned about embryonic and fetal development and the impact of teratogens on development.
This is also an opportunity to consider the organ systems that develop either late in the fetal period (respiratory, genitalia) or continue developing postnatally (neural).
Don't forget the now added BGDA Frequently Asked Questions page.
Pregnancy is also a biological interaction between mother and fetus, effects on the mother of pregnancy (ectopic pregnancy, gestational diabetes, pre-eclampsia) will not be covered in this current lab.
Please email Dr Mark Hill if you wish to make a comment about this current project.
Beginnings, Growth and Development