The palm normally has three flexion creases. Sometimes, the two horizontal creases fuse to form a single crease, called a single palmar crease or a simian crease.
Many structures develop in the fetus in the first few months of gestation .
Palmar creases develop early, by the 11th to 12th week of gestation. Abnormalities in palmar creases may indicate problems with the early development of the fetus and other associated abnormalities. A single palmar crease or simian crease appears in approximately 1 out of 30 normal people. Of normal people with simian creases, males are twice as likely as females to exhibit this trait. What to expect at your health care provider's office An infant with a simian crease generally has other symptoms and signs that, when taken together, define a specific syndrome or condition.