Obstetric Topic 51. Main forms of congenital malformations

I. Basic Concepts

Definition and Causes

• Congenital malformation: structural or functional abnormality present at birth due to abnormal intrauterine development.
• Causes: chromosomal/genetic disease, multifactorial inheritance, teratogen, infection, maternal disease or unknown.
• Main prenatal logic: anomaly scan → search associated anomalies → genetic counseling/testing when major or multiple anomalies are present → plan delivery/neonatal care.

II. Cardiovascular Malformations

Clinical Classification

• Left-to-right shunts: not cyanotic at birth; chronic pulmonary hypertension may later convert to right-to-left shunt → Eisenmenger syndrome.
• Right-to-left shunts: early cyanosis.

Left-to-Right / Acyanotic

• ASD: failure/defect of atrial septum development.
• VSD: most common congenital heart defect; membranous part most common; small defects may close spontaneously.
• PDA: failure of ductus arteriosus closure → oxygenated blood returns to pulmonary circulation.
• Coarctation of aorta: narrowing of aortic outflow; infantile/preductal form may be duct-dependent.

Right-to-Left / Cyanotic

• Tetralogy of Fallot: VSD + pulmonary stenosis + overriding aorta + right ventricular hypertrophy.
• Transposition of great arteries: aorta from RV and pulmonary artery from LV; survival requires mixing by PDA/ASD/VSD until surgery.

III. CNS Malformations

• Anencephaly: failure of anterior neural tube closure → absent major brain/skull vault; lethal.
• Spina bifida: incomplete spinal neural tube closure; severe form = myelomeningocele with meninges + spinal cord protrusion.
• Hydrocephalus: excess CSF from obstruction or poor absorption → ventriculomegaly/enlarged head.
• Microcephaly: abnormally small brain/head; causes include genetic disease, rubella/other congenital infections and teratogens.
• Neural tube defect risk decreases with periconceptional folic acid.

IV. GI, Abdominal Wall and Craniofacial Defects

GI and Abdominal Wall

• Esophageal atresia: blind-ended esophagus; feeding difficulty/choking and polyhydramnios.
• Omphalocele: midline herniation into umbilical cord, membrane-covered; high association with chromosomal/cardiac anomalies.
• Gastroschisis: paraumbilical abdominal wall defect, no covering membrane; usually fewer chromosomal associations but bowel injury risk.
• Anal atresia: absent/malpositioned anus or no meconium → urgent neonatal surgical assessment.

Cleft Lip and Palate

• Cleft lip/palate: failed fusion of maxillary and medial nasal processes/palatal shelves.
• Problems: feeding difficulty, speech issues, recurrent otitis/hearing problems.

V. Renal, Genitourinary and Musculoskeletal Defects

Renal and Genitourinary

• Bilateral renal agenesis: absent kidneys → anuria → severe oligohydramnios → Potter sequence and lethal pulmonary hypoplasia.
• Potter sequence: oligohydramnios → fetal compression + poor lung development → flat face, limb deformities, pulmonary hypoplasia.
• Mullerian agenesis / Mayer-Rokitansky-Kuster-Hauser syndrome: absent uterus/upper vagina.
• Unicornuate uterus: development of only one Mullerian duct.
• Bicornuate uterus: partial fusion failure → heart-shaped uterus.
• Septate uterus: failure of septal resorption after Mullerian duct fusion.
• Vaginal septum: longitudinal = failure of lateral fusion; transverse = failure of vertical fusion between Mullerian system and urogenital sinus.

Musculoskeletal

• Clubfoot: foot rotated inward/downward; may be isolated or syndromic.
• Polydactyly: extra fingers/toes; isolated familial or part of chromosomal/syndromic disease.
• Achondroplasia: genetic cartilage-growth disorder → short limbs, normal trunk, usually normal intelligence.

VI. Chromosomal Disorders

• Down syndrome: trisomy 21 → flat face, epicanthic folds, hypotonia/intellectual disability, congenital heart defects.
• Edwards syndrome: trisomy 18 → clenched hands with overlapping fingers, rocker-bottom feet/clubfoot, cardiac/renal malformations, severe intellectual disability.
• Patau syndrome: trisomy 13 → microcephaly/holoprosencephaly, cleft lip/palate, polydactyly, cardiac/renal malformations, severe intellectual disability.