BIRTH DEFECTS / CONGENITAL MALFORMATIONS / CONGENITAL ANOMALIES Lecture – Anatomy Lectures – MBBS Lectures

 Define teratology & teratogenesis
 Enumerate types of birth abnormalities & define
each of them with at least one example
 Summarize principles of teratology
 Classify teratogens with associated human
malformations in tabulated form

Birth defects may be:
• Structural
• Functional
• Metabolic

 TERATOLOGY:
 is the branch of science that studies the
causes, mechanisms & patterns of
abnormal development
 TERATOGENESIS
 The processes of production of birth
defects in the embryo/fetus

Causes of birth defects:

Minor anomalies serve as clues for diagnosing more serious underlying defects

TYPES OF ABNORMALITIES

For prevention of birth defects, initiate prevention strategies
prior to conception

Malformation

Disruptions & Deformations

Syndrome

Malformation , Disruption & Deformation

 Syndrome:
 is a group of anomalies occurring together that
have a specific common cause. A diagnosis has
been made & the risk of recurrence is known.
 Sequence:
 is a pattern of multiple anomalies derived from a
single known or presumed structural defect or
mechanical factor. In the case of a sequence, the
primary initiating factor and cascade of secondary
developmental complications are known. For
example, the Potter sequence, attributed to
oligohydramnios, results from either renal agenesis
or leakage of amniotic fluid.

 Association:
 is the nonrandom appearance of two or more
anomalies that occur together more frequently
than by chance alone, but whose cause has not
been determined.
 An association, in contrast to sequence, refers to
statistically, not pathogenetically or causally, related
defects.
 One or more sequences, syndromes, or field defects
may very well constitute an association

Association

 CHARGE
o Colobomas,
o Heart defects,
o Atresia of the choanae,
o Retarded growth,
o Genital anomalies, and
o Ear abnormalities

 VACTERL
o Vertebral,
o Anal,
o Cardiac,
o Tracheo Esophageal,
o Renal &
o Limb anomalies

Although they do not constitute a diagnosis, associations are important
because recognition of one or more of the components promotes the
search for others in group.

A teratogen is any agent that can produce a
congenital anomaly or increase the incidence of
an anomaly in the population

ENVIRONMENTAL FACTORS – TERATOGENS

 Teratogens do not appear to be effective in causing
anomalies until cellular differentiation has begun;
however, their early actions (e.g., during the first 2
weeks) may cause the death of the embryo.
o Environmental disturbances during the first 2 weeks
after fertilization may interfere with cleavage of the
zygote and implantation of the blastocyst and/or cause
early death and spontaneous abortion of the embryo;
however, they are not known to cause congenital
anomalies in human embryos
o Teratogens acting during the first 2 weeks either kill the
embryo or their disruptive effects are compensated for
by powerful regulatory properties of the early embryo.
Most development during the first 2 weeks is concerned
with the formation of extraembryonic structures such as
the amnion, umbilical vesicle (yolk sac), and chorionic sac

 Each tissue, organ, and system of an embryo
has a critical period during which its
development may be disrupted
 The type of congenital anomaly produced
depends on which parts, tissues, and organs
are most susceptible at the time that the
teratogen is active.

PRINCIPLES OF TERATOLOGY

Factor determining the capacity of an agent to
produce birth defects have been defined and
set forth as the principles of teratology

1. Genotype of conceptus
   o Maternal genome
2. Developmental stage at time of exposure
3. Dose & duration of exposure to a teratogen
4. Teratogens act in specific ways (Mechanisms)
5. Manifestations of abnormal development

Development of the embryo is most easily
disrupted when the tissues and organs are
forming.
During this Organogenetic Period teratogens
may induce major congenital anomalies.

Causes of birth defects

TERATOGENS ASSOCIATED WITH HUMAN MALFORMATIONS

• INFECTIOUS AGENTS
• PHYSICAL AGENTS
• CHEMICAL AGENTS
• HORMONES

INFECTIOUS AGENTS

VIRUSES:

1.Rubella virus

2. Cytomegalovirus
3. Heroes Simplex Virus
4. Vaicella Virus

BACTERIAL INFECTIONS:

Toxoplasmosis

Herpes simpex virus

Varicella virus

Human immunodeficiency virus

Other viral infections & hypothermia

•Measles, mumps, hepatitis, poliomyelitis, echovirus,
coxsackie virus, & influenza
•Hepatitis B, A, C & E