Micrognathia fetal ultrasound

Prevalence:

• 1 in 1,500 births.

Ultrasound diagnosis:

• Subjective finding of prominent upper lip and receding chin in the mid-sagittal view of the face. These findings may be due to micrognathia (short mandible) or retrognathia (backward displacement of the mandible).
• Severe micrognathia is associated with polyhydramnios (>25 weeks’ gestation), due to glossoptosis (normal tongue obstructing small oral cavity).

Associated abnormalities:

• Chromosomal abnormalities, mainly trisomy 18 and triploidy, are found in about 30% of cases.
• Associated with >50 genetic syndromes, including:
  • Pierre–Robin anomalad: micrognathia or retrognathia, cleft palate and glossoptosis. In half of cases this a sporadic isolated finding and in the other half it is associated with other anomalies or with recognized genetic and non-genetic syndromes).
  • Treacher Collins syndrome: autosomal recessive or autosomal dominant with 60% de novo mutations; hypoplasia of the maxilla and zygomatic bone, micrognathia, cleft palate and malformed or absent ears.
  • Otocephaly: sporadic: severe micrognathia or agnathia, and mid-line defects, including holoprosencephaly, anterior encephalocele, cyclopia, aglossia, and mid-facial location of the ears.

Investigations:

• Detailed ultrasound examination.
• Invasive testing for karyotyping and array.

Follow up:

• Ultrasound scans every 4 weeks to monitor growth and amniotic fluid.

Delivery:

• Place: hospital with facilities for neonatal intensive care.
• Time: 38 weeks.
• Method: induction of labor aiming for vaginal delivery. A pediatrician should be present in the delivery room and be prepared to intubate the neonate.

Prognosis:

• Neonatal mortality: >80% due to associated abnormalities.
• In Pierre–Robin anomalad survival is good.

Recurrence:

• Isolated: no increased risk of recurrence.
• Part of trisomies: 1%.
• Part of genetic syndromes: 25% to 50%.