- Approximately 2% of live births have major congenital abnormality
- Incidence is increased in pre-term and small for gestational age infants
- Malformation = disturbance of growth during embryogenesis
- Deformation = late change in previously normal structure due to intrauterine factors
Causes of deformations
- Primigravidity
- Oligohydramnios
- Abnormal presentation
- Multiple pregnancy
- Uterine abnormality
Causes of malformations
| Cause |
Percentage |
| Mendelian genetic aberration |
20 |
| Chromosomal |
10 |
| Teratogens |
10 |
| Multiple factors |
30 |
| Unknown |
30 |
Anatomical systems involved
| Malformation |
Rate per 10,000 birth |
| All |
165 |
| Heart |
35 |
| Genital organs |
25 |
| Urinary system |
20 |
| Central nervous system |
15 |
| Limbs |
15 |
Teratogenesis
- Teratogen = drug, chemical or virus that can cause fetal malformation
- Act during critical period of fetal development
- Critical period varies between organs
- Brain 15-25 days
- Eye 25-40 days
- Heart 20-40 days
- Limb 24-36 days
Drugs as teratogens
- Hormones – progestogens, diethyl stilbeostrol, male sex hormones
- Antipsychotics – lithium, haloperidol, thalidomide
- Anticonvulsants – sodium valproate, carbamazepine, phenobarbitone
- Antimicrobials – tetracycline, chloramphenicol, amphotericin B
- Antineoplastics – alkylating agents, folic acid antagonists
- Anticoagulants – warfarin
- Antithyroid agents – carbimazole, propylthiouracil
- Others – toluene, alcohol, marijuana, narcotics
Microbial agents as teratogens
- Rubella
- Toxoplasmosis
- Syphilis
- Cytomegalovirus
- Coxsackie B virus
Bibliography
Roizen N J, Patterson D. Down's syndrome. Lancet 2003; 361: 1281-1289. |