Abnormal Fetal Posture/Movement

Janice L. B. Byrne, MD

DIFFERENTIAL DIAGNOSIS

Common

Spina Bifida
Trisomy 18
Arthrogryposis, Akinesia Sequence
Fetal Constraint

Less Common

Body Stalk Anomaly
Caudal Regression Sequence
Fetal Hypoxia/Severe Hypotonia
Amniotic Bands
Fetal Neck Masses
Joint Dislocation
Vertebral Segmentation Abnormalities

Rare but Important

Iniencephaly
Multiple Pterygium Syndrome

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Postural abnormalities
- Is the abnormality fixed or does the position normalize with fetal movement?
- Is the abnormal body posture associated with an obvious anomaly?
Fetal movement abnormalities
- Is the movement abnormality progressive over time or an acute change?
- Is there evidence of arthrogryposis?
- Is there associated oligohydramnios, polyhydramnios, osteopenia or edema/hydrops?
- Is the fetus normally grown?
- Can normal movement be elicited by acoustic stimulation?
  - Normal sleep cycle vs. pathologic lack of movement

Helpful Clues for Common Diagnoses

Spina Bifida
- Lack of movement of the lower extremities associated with clubfeet ± ventriculomegaly
- Abnormal calvarium shape (“lemon” sign) with small abnormal posterior fossa (“banana” sign)
Trisomy 18
- Arthrogryposis of multiple joints may be seen
- Severe symmetrical growth restriction (IUGR) and multiple anomalies common
Arthrogryposis, Akinesia Sequence
- Fixed contractures of multiple joints, often severe
- Joint abnormalities due to fetal akinesia
  - Bilateral and symmetrical
- Upper and lower extremities may be equally affected or discordant in severity
- Associated polyhydramnios due to decreased swallowing
- Skin edema, osteopenia, frank hydrops often late findings, especially in lethal cases
Fetal Constraint
- Multiple gestation
  - Postural abnormalities due to crowding
  - True deformations may result (clubfeet, torticollis, plagiocephaly)
- Fibroids
  - Large submucosal or multiple smaller fibroids
- Uterine anomaly
  - Associated malposition common
- Severe oligohydramnios
  - Premature rupture of membranes
  - Twin-twin transfusion donor twin
  - Severe IUGR, genitourinary anomalies

Helpful Clues for Less Common Diagnoses

Body Stalk Anomaly
- Severe postural abnormalities
- Rotary scoliosis with unusual angulation of extremities from the body axis
- Lack of free floating umbilical cord
- Large schisis defects of abdomen &/or thorax seen, often with adherence of defect to the placenta
Caudal Regression Sequence
- Absent sacrum with hypoplastic lower extremities
- Legs held in a fixed, “Buddha” or “crossed-legged tailor’s” posture
- More common in poorly controlled diabetes
Fetal Hypoxia/Severe Hypotonia
- Decreased or absent fetal breathing, tone and movement
- Increased risk of fetal/neonatal birth asphyxia, neurologic injury, seizures
- Chronic hypoxia from severe uteroplacental insufficiency
  - IUGR, oligohydramnios
  - Abnormal Dopplers with absent or reversed end diastolic flow, pulsatile ductus venosus
- Causes of acute hypoxia
  - Abruptio placenta
  - Severe maternal hypoxemia (trauma, cardiopulmonary arrest, asphyxia)
- Severe hypotonia: May be acute or chronic
  - Hyperextended or hyperflexed neck
  - Usually due to underlying neurologic abnormality
Amniotic Bands
- Wide spectrum of disruptions, often associated with postural abnormalities
  - Fetus may appear tethered
- Membrane strands may be visible in amniotic cavity
Fetal Neck Masses
- Postural abnormality of neck may be progressive
- Decreased fetal swallowing → development of polyhydramnios → increased risk of airway obstruction
- Goiter
  - Neck hyperextension with large goiter
  - Sagittal view to evaluate position of head and neck; mode of delivery or airway at birth unlikely to be affected if normal neck flexion observed
- Cystic hygroma (lymphangioma)
  - Large and asymmetrical masses lead to significant postural abnormality of head and neck
Joint Dislocation
- More common in hips, knees
Vertebral Segmentation Abnormalities
- Hemivertebrae, missing vertebral segments, abnormal ribs associated with scoliosis

Helpful Clues for Rare Diagnoses

Iniencephaly
- Persistent “stargazer” posture of head, neck due to fixed cervical hyperextension, cervical neural tube defect
- Other malformations common
Multiple Pterygium Syndrome
- Fixed joint contractures associated with abnormal posture
- Pterygia may not be visualized on ultrasound
- Cystic hygroma and hydrops in lethal type

Other Essential Information

Hydrops and polyhydramnios with arthrogryposis predict high risk for lethality
If decreased or absent fetal movement, search for evidence of acute or chronic condition
- If acute, fetal hypoxia is likely and delivery may be life saving
If abnormal posture, evaluate for evidence of associated fetal or uterine abnormality to determine underlying cause

Image Gallery

Axial ultrasound shows a sac

overlying a large lumbosacral myelomeningocele

in a mid-trimester fetus.

Clinical photograph shows term newborn with lumbosacral neural tube defect. Note the bilateral clubfeet

and atrophic legs

held in an abnormal posture.

(Left) Transabdominal ultrasound shows a typical case of arthrogryposis associated with trisomy 18. The hand

was persistently held in an abnormal orientation to the wrist. The legs were held in extension, and the left foot was clubbed. (Right) Clinical photograph shows a stillborn term infant with trisomy 18. Arthrogryposis with multiple joint contractures can be seen