When performing a lumbar puncture on a term newborn, what is the recommended needle depth?

• A. 0.5 - 1 cm
• B. 1 - 1.5 cm
• C. 2 - 2.5 cm
• D. 3 - 4 cm

Answer: (B)

Neonatal lumbar puncture requires only a short depth to reach the subarachnoid space because the tissues are thin and the CSF space lies close beneath the skin. For a term newborn, about one to one and a half centimeters of needle advancement from the skin is typically enough to enter the intrathecal space and obtain CSF.

Going deeper than this increases the risk of hitting neural structures, as the spinal cord in newborns ends lower in the canal (around the L3 level), so a deeper needle can raise the chance of cord or nerve root injury. A depth as shallow as half a centimeter is often insufficient to reach the CSF in many term infants, while depths of two to four centimeters are unnecessarily deep and riskier.

Therefore, the recommended needle depth to reach the subarachnoid space in a term newborn during a lumbar puncture is about 1 to 1.5 cm.