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.
|AETIOLOY OF BIRTH DEFECTS|
|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|
|Hypertrophic pyloric stenosis|
|Abdominal wall defect (Exomphalos and gastroschisis)|
- Antenatal History
- Perinatal History
- Postnatal History
- Social History – smoking, alcohol
- Family History – miscarriage, stillbirths, genetic diseases
- Head to Toe
|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
- Nuchal translucency screening
- Diagnostic tests.
- Chorionic villus sampling
- Fetal blood samples
- Organ biopsies
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|
|Advanced maternal age|
|Exposure to radiation or drugs during pregnancy|