Birth Defects

Overview Birth defects are the leading cause of perinatal and post- neonatal deaths, and result in substantial morbidity and disability in developed countries. There is a wide variety of mechanisms including genetic, environmental and multifactorial. Major birth defects affect 2–3% of live-borns, and minor birth defects affect 15%. Preventative strategies remain limited, but include maternal folic acid supplementation, reduction in teratogen exposure, alternative reproductive options, prenatal detection and neonatal screening.

Definition Types of structural birth defects
Malformation arise during the initial formation of the embryo and fetus as a result of genetic and/ or environmental factors during organogenesis (2–8 weeks post-conception). Malformations may include failure of formation, incomplete formation or abnormal configuration. Examples include spina bifida, cleft palate and hypospadias.
Disruption result from a destructive process that alters structures after formation. Examples include early amnion rupture causing amputation defects of digits, and vasoconstriction defects caused by cocaine.
Deformations result from moulding of a part by mechanical forces, usually acting over a prolonged period. Examples include talipes, congenital hip dislocations and plagiocephaly associated with oligohydramnios.


Mechanism Examples
Whole chromosome duplication Downsyndrome (Trisomy 21)
Whole chromosome missing Turner (monosomy XO)
Section of a chromosome duplicated Cat eye syndrome (Duplication 22q)
Section of a chromosome missing Cri du chat syndrome (Deletion 5p)
Mutation of single gene Smith-Lemli-Opitz syndrome (7-Dehydrocholesterol reductase)
Multifactorial/polygenic (Genes and envinroment) Congenital Heart defect, Neural tube defect and facial cleft
Uterine environment Hip dysplasia, talipes (Oligohyrdomnios)
Wider environment Fetal rubella syndrome (Rubella infection in pregnancy)
Fetal Alcohol syndrome (maternal alcohol ingestion)
Microcephaly (high dose irradiation)
Limb deficiency (thalidomide)
Noonan Syndrome is an autosomal dominany disorder with mutation of chromosome 11. Clinical features include characterisic facies (down slatning, palpebral fissures, widespread eyes, low set ears +/- ptosis), Short stature, pulmonary valve stenosis, webbed neck, failure to thrive, abnormalities of cardiac conduction and rhythm.
Common Birth Defects Descrption
Congenital Heart defect
Development hip dysplasia
Talipes equinovarus
Hypertrophic pyloric stenosis
Down syndrome
Cleft lip/palate
Spina bifida
Tracheo-eosphageal fistula
Abdominal wall defect (Exomphalos and gastroschisis)


  • History
    • Antenatal History
    • Perinatal History
    • Postnatal History
    • Social History - smoking, alcohol
    • Family History - miscarriage, stillbirths, genetic diseases
  • Examination
    • Head to Toe
    • Mesurements
  • Investigaitons
Remember Features of Down syndrome Hypotonia, Protruding tongue, Intellectual delay, Brachycephaly, Inner epicanthal folds, Hearing loss, Short neck, Single palmar crease, 40% have cardiac anomaly

Prenatal Diagnosis aims at detection of birth defects prior to birth to allow options for parents. Tests fall into two main categories:

  • Screening tests
    • Ultrasound
    • Nuchal translucency screening
  • Diagnostic tests.
    • Aminocentesis
    • Chorionic villus sampling
    • Fetal blood samples
    • Organ biopsies
    • MRI
    • Ultrasound


Overview Teratogens is an environmental agent that can cause abnormalities of form or function in an exposed embryo or fetus (examples: sodium valproate and alcohol). Estimated ~ 1% and 3% of birth defects may be related to teratogenic exposure.

  • <2weeks after contraception - exposure of teratogen is likely to cause embronynic death rather than malformation (all or nothing effect)
  • 2-8 weeks after contraception - During organogenesis exposure to teratogens may cause malformation
  • >8 weeks after contraception - slowly forming organs such as brain and kidney can be effected by teratogen exposure resulting in cognitive impairment, or behavioral effects
Indications for genetic couselling
Parents with genetic disorders
Couples who have had a still birth
Couples who have had a child with birth defect or intellectual disability
Family history of known genetic disorders
Recurrent miscarriage
Advanced maternal age
Exposure to radiation or drugs during pregnancy