Final answer:
Cleft lip more commonly occurs on the left side, but it can also be present on the right side or both sides. It results from a failure in the fusion of facial structures during embryonic development, and surgical repair is typically necessary.
Step-by-step explanation:
Cleft lip is a developmental defect where there is a partial or complete failure of the right and left portions of the upper lip to fuse together, creating a cleft or gap. It is a common condition, affecting approximately 1:1000 births, predominantly in males. When it comes to the occurrence of a cleft on one side over the other, the cleft lip is more commonly found on the left side. However, it can also occur on the right side or affect both sides.
During embryonic development, the maxilla bones and overlying muscle and skin join at the midline to form the upper lip. A similar process occurs in the formation of the hard palate. Should an error arise in these processes, a birth defect of cleft lip or cleft palate may result. Cleft palate is another, more severe, developmental defect affecting the bony structure of the hard palate and is more common in females.
Surgical repair is required to correct these defects, as they can lead to complications such as malnutrition in infants who may struggle to generate the necessary suckling for nursing due to a cleft palate.