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Cardiovascular Block: Week 7 > Mechanisms of Structural Birth Defects > Flashcards

Mechanisms of Structural Birth Defects Flashcards

1
Q

Why do birth defects occur?

A

Birth defects occur due to abnormal development in a particular part of the embryo at a particular point in time.
- Timing = NB!

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2
Q

What are the 3 phases of normal fetal growth and development?

A
  1. Preimplantation (0-21 days)
  2. Embryonic (22-55 days)
  3. Fetal stage (56 days - birth)
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3
Q

During which phase of normal fetal growth and development does the development of the organs and major structures occur?

A

During the embryonic period

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4
Q

What is the pre-implantation phase also known as?

A

The all-or-nothing phase

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5
Q

What occurs during the fetal phase of growth and development?

A

Period of growth

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6
Q

What is Day 0?

A

Day 0 = day of conception (as defined by embryologists)

Note: obstetricians work from the last period (2 weeks before conception)

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7
Q

What is a birth defect or congenital abnormality? (Broadest definition)

A

Any abnormality of structure or function that is present, although not necessarily obvious, at the time of birth.

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8
Q

What categories of birth defects are seen?

A

May be:

  • Major (serious, potential to cause disability or death) / minor (cosmetic)
  • Single / multiple
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9
Q

What is the epidemiology of birth defects?

A

30% of all pregnancies are affected by morphological errors - most lost spontaneously
- 3-5% of all babies are born with a serious congenital abnormality (globally)

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10
Q

What are pre-conception causes of birth defects?

A
  1. Chromosomal
  2. Single gene
  3. Multifactorial
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11
Q

What are post-conception causes of birth defects?

A
  1. Teratogens

2. Abnormal fetal environment

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12
Q

An abnormality in the development of the embryo or fetus is classified according to what 4 categories?

A
  1. Malformation
  2. Deformation
  3. Disruption
  4. Dysplasia
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13
Q

What is a malformation?

A

Abnormal structure caused by complete or partial failure of development of an organ or limb (part of the primary developmental pattern, something was always going to go wrong)
= Non-progressive congenital abnormality

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14
Q

When do malformations occur?

A

Occurs in the embryonic period (early)

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15
Q

What are some of the causes of malformations?

A
  1. Chromosome abnormalities
  2. Single gene abnormalities
  3. Multifactorial
  4. Teratogens (e.g. Alcohol, Rubella, Maternal Diabetes) BUT only if exposed right from the beginning, never having the chance to develop normally
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16
Q

What is the recurrence rate of malformations?

A

Depends on cause

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17
Q

What are examples of multifactorial malformations?

A
  1. Cleft lip / palate

2. Neural tube defect

18
Q

What is an example of a chromosomal malformation?

A

Trisomy 13

19
Q

What is an example of a single gene malformation?

A

Split foot

20
Q

What are the frequencies of malformations due to the following causes?

  • Chromosomal
  • Single gene
  • Teratogens
  • Multifactorial
  • Unknown
A
  • Chromosomal = 10%
  • Single gene = 14%
  • Teratogens = 10%
  • Multifactorial = 23%
  • Unknown = 43%
21
Q

What is a deformation?

A

Normal underlying structure; but normal structure is pushed / pulled out of shape (external mechanical force)

22
Q

When do deformations occur and what tissue is usually involved?

A

Usually occurs later in pregnancy and often involves bone, cartilage and joints

23
Q

What are causes of deformations?

A
  • Abnormal uterus (large fibroids, bicornuate)
  • Multiple pregnancy
  • Oligohydramnios
24
Q

What is the recurrence risk of deformations?

A

Recurrence risk is usually low and they are often correctable after birth

25
Q

What are examples of deformation?

A
  1. Clubfoot

2. Plagiocephaly (due to pressure from twin, corrects itself spontaneously)

26
Q

What are the two types of clubfoot seen in infants?

A
  1. Malformation: due to abnormal bone formation

2. Deformation: due to mechanical force, easily correctible with physio etc. (underlying structure is normal)

27
Q

What is a disruption?

A

Normal underlying tissue; but normal structure is destroyed (limb, organ or tissue)

  • particular anatomical area is usually involved
  • different tissues in that area destroyed
28
Q

What are some causes of disruptions?

A
  1. Ischemia (amniotic bands, fetal intravascular accidents)

2. Necrosis following infection (fetal VZV)

29
Q

What is the recurrence risk of disruptions?

A

Recurrence risk usually low

30
Q

What is an example of a disruption?

A

Constriction ring due to an amniotic band

31
Q

What is dysplasia?

A

Abnormal organization and functioning of a specific tissue type throughout the body e.g. skeletal dysplasia
- Abnormality continues as long as the tissue grows and functions

32
Q

What causes dysplasia?

A

Single gene defects

33
Q

What is the recurrence risk of dysplasia?

A

Dependent on Mendelian Inheritance

34
Q

What is the most common skeletal dysplasia?

A

Achondroplasia

35
Q

What are other examples of dysplasia?

A
  1. Ostogenesis imperfecta

2. Thanatophoric dysplasia

36
Q

What is the significance of multiple abnormalities?

A

Many healthy people have 1 or even 2 minor abnormalities.

BUT >/= 3 anomalies, even if minor, are much more likely to be part of an underlying syndrome or sequence or association

37
Q

What is a syndrome?

A

Recognizable pattern of symptoms, signs and dysmorphic features with a known or strongly suspected genetic cause
e.g. Down Syndrome / Trisomy 21

38
Q

What is a sequence?

A

A sequence is the result of a “cascade” of events in which one abnormality leads to further abnormalities
e.g. Potter sequence (begins with kidneys that didn’t develop which leads to multiple other problems)

39
Q

What is an association?

A

A collection of major malformations that occur together more often than would be expected by chance and cannot be recognized as a syndrome or sequence.
e.g. VACTERL

40
Q

What is VACTERL

A 
V = Vertebral / rib anomaly 
A = Anal atresia 
C = Cardiac 
TE = Tracheoesophageal fistula 
R = Radial anomaly 
R = Renal 
L = Limb defects 
(3 or more in at least 2 or more parts of the body = association once all other known syndromes are excluded)
41
Q

What is the relevance of the mechanism of structural birth defects?

A

Plays a role in:

  • Diagnosis / further intervention
  • Prognosis
  • Management
  • Recurrence risks
  • Prevention including prenatal diagnosis

Cardiovascular Block: Week 7 (5 decks)

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