Foundations Practical - Critical Periods

Human critical periods of development

We have now had a very quick trip through more than 9 months of development in nearly 2 hours. Before we finish it is worth thinking about times in development when things may go wrong.

Environment Effects

These are developmental times (stages) sensitive to insult, be aware of these times, the causes and the potential effects.

Critical periods of development refer to times when genetic or materal effects can impact upon the developmental process. The timing of these effects will impact on different systems at different times.

Conceptus		Embryonic development (weeks)											Fetal period (weeks)
1	2	3		4			5	6		7		8	9	16	20-36	38

		Neural
			Heart
				Upper limbs
					Lower limbs
					Ear
						Eye
									Palate
									Teeth
											External genitalia
Loss		Major abnormalities										Functional and Minor abnormalities

Links: Embryonic Development | Timeline human development | Movie - Human Development annotated cartoon | Human - critical periods | Human Abnormal Development

Systems with long periods of development or complex developmental origins are more susceptible to developmental abnormalities.

Which systems will take a long time to develop?
Which systems are complex in origin?

Australian Statistics

Australian Congenital Anomalies Monitoring System (ACAMS) contains data based on notifications of major congenital anomalies to birth defects registers in New South Wales, Victoria, Western Australia and South Australia and on data collected on congenital anomalies in Queensland, Tasmania and the Australian Capital Territory. Information is included on live births and stillbirths of 20 weeks gestational age or more or 400 grams birthweight or more (including induced abortions) with a congenital anomaly. Congenital anomalies are coded using the British Paediatric Association Classification of Diseases (ICD-9-BPA), which is based on the International Classification of Diseases, 9th Revision (ICD-9). ACAMS

USA Statistics

USA Selected Abnormalities (CDC National estimates for 21 selected major birth defects 2004–2006)
Birth Defects	Cases per Births (1 in ...)	Estimated Annual Number of Cases
anencephaly	4,859	859
spina bifida without anencephaly	2,858	1,460
encephalocele	12,235	341
Anophthalmia/microphthalmia	5,349	780
patent ductus arteriosus‎/common truncus	13,876	301
transposition of the great vessels	3,333	1,252
Tetralogy of Fallot	2,518	1,657
atrial septal defects/ventricular septal defects	2,122	1,966
hypoplastic left heart	4,344	960
cleft palate without cleft lip	1,574	2,651
cleft lip with and without cleft palate	940	4,437
Esophageal atresia/tracheoesophageal fistula	4,608	905
Rectal and large intestinal atresia/stenosis	2,138	1,952
Reduction deformity, upper limbs	2,869	1,454
Reduction deformity, lower limbs	5,949	701
gastroschisis	2,229	1,871
omphalocele	5,386	775
Diaphragmatic hernia	3,836	1,088
Trisomy 13	7,906	528
Trisomy 21 (Down syndrome)	691	6,037
Trisomy 18	3,762	1,109
Links: Human Abnormal Development \| CDC Birth Defects - Data & Statistics \| USA Statistics \| Victoria 2004 \| USA 2006 \| Europe 2010

Genetic

Links: Genetics

Fetal Origins Hypothesis

The Fetal period is also potentially sensitive to maternal effects that impact upon interuterine growth. Along these lines there is growing evidence that low birth weight, and therefore inhibited fetal growth, has postnatal effects on lifelong health outcomes.

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Cite this page: Hill, M.A. (2024, April 19) Embryology Foundations Practical - Critical Periods. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Foundations_Practical_-_Critical_Periods

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