Prevalence:

• 1 in 25,000 births.

Ultrasound diagnosis:

• Short limbs, short hands and fingers, large head with frontal bossing and depressed nasal bridge, and lumbar scoliosis.
• Limb shortening and typical facial features become apparent >22 weeks’ gestation.

Investigations:

• Detailed ultrasound examination.
• Achondroplasia is due to a mutation in the FGFR3 gene and has autosomal dominant inheritance pattern. The diagnosis can be made by invasive testing or cfDNA analysis of maternal blood.

Follow up:

• Follow-up scans every 4 weeks to monitor growth of the fetal head.

Delivery:

• Standard obstetric care and delivery.
• Cesarean section if the fetal head circumference is >40 cm.

Prognosis:

• Homozygotic type: lethal due to severe pulmonary hypoplasia.
• Heterozygotic type: intelligence and life expectancy are normal. Respiratory limitations due to small thorax and development of stenotic vertebral canal (peripheral neurologic deficits) may decrease the quality of life.

Recurrence:

• One affected parent: 50%.
• If both parents are affected: 50% risk of heterozygous achondroplasia, 25% risk of homozygous achondroplasia and 25% chance of unaffected child.
• De novo mutation: low recurrence risk.