Clefts are openings or splits in the upper lip, the roof of the mouth (palate), or both that form when facial tissues don’t fully fuse during early pregnancy. They are one of the most common birth differences worldwide, affecting roughly 1 in 700 live births. A cleft can range from a small notch in the lip to a gap that runs through the entire palate, and the severity depends on exactly when the normal fusion process was interrupted.
How Clefts Form
During the fourth through twelfth weeks of pregnancy, separate pieces of tissue on either side of a baby’s face grow toward the midline and join together. The lip structures fuse first, followed by the palate, which closes from front to back and finishes with the small tissue at the very back of the mouth (the uvula). If something disrupts this process at any point, the tissues don’t meet, leaving a gap. The earlier the disruption occurs, the more extensive the cleft tends to be.
Several signaling molecules guide this fusion. When any of these molecular signals fail, the palate shelves may not grow wide enough, may not lift into position above the tongue, or may not stick together at the midline. The process is tightly choreographed, which is part of why clefts are so common compared to other structural birth differences.
Types of Clefts
Clefts are classified by location and extent:
- Cleft lip, unilateral: a split on one side of the upper lip. It can be incomplete (stopping below the nostril) or complete (extending up into the nostril).
- Cleft lip, bilateral: splits on both sides of the upper lip, which can also be complete or incomplete.
- Cleft palate, incomplete: an opening in part of the roof of the mouth, usually toward the back.
- Cleft palate, complete: a gap that runs from behind the upper teeth all the way to the back of the palate.
A baby can have a cleft lip alone, a cleft palate alone, or both together. Cleft lip with or without cleft palate and isolated cleft palate are actually considered distinct conditions with somewhat different genetic profiles. About 50% of isolated cleft palate cases occur as part of a broader syndrome involving other features, compared to around 30% of cleft lip cases. The remaining cases are called nonsyndromic, meaning the cleft is the only structural difference.
Causes and Risk Factors
Most clefts result from a combination of inherited genetic tendencies and environmental exposures during pregnancy. No single gene causes the majority of cases. Instead, variations across many genes each nudge the risk slightly higher, and environmental factors can tip the balance.
Smoking during pregnancy is one of the clearest modifiable risk factors. In one large study, about 21% of mothers of babies with clefts smoked during pregnancy, compared to 16% of mothers whose babies did not have clefts. Pre-existing diabetes (the type present before pregnancy, not gestational diabetes) has also been linked to a roughly doubled risk of cleft lip. Maternal obesity may play a role as well, potentially through pollutants stored in fat tissue or through metabolic changes that affect fetal development.
Certain genetic syndromes carry a high likelihood of clefting. Van der Woude syndrome, caused by mutations in specific genes involved in skin and tissue development, is one of the most well-known. Conditions like Pierre Robin sequence, Stickler syndrome, and Treacher Collins syndrome can also lead to cleft palate because they affect jaw growth, which in turn crowds the tongue upward and physically blocks the palate shelves from closing.
Feeding Challenges
Babies with cleft palates often struggle to feed because the gap in the roof of the mouth makes it difficult to create the suction needed for breastfeeding or standard bottle feeding. Milk can flow into the nasal cavity, and the baby may tire quickly from the extra effort. This doesn’t mean breastfeeding is impossible, but most families need guidance and adapted equipment.
Specialty bottles with squeezable reservoirs or one-way valves help deliver milk without requiring the baby to generate strong suction. Palatal obturators, which are small custom plates that temporarily cover the gap, are sometimes used but haven’t been shown to significantly improve growth compared to specialty bottles alone. What does consistently help is early education and coaching from feeding specialists, which gives parents practical techniques for positioning, pacing, and burping.
How Clefts Affect Hearing
Children with cleft palates have a much higher rate of fluid buildup in the middle ear, and the reason is mechanical. The Eustachian tube connects the middle ear to the back of the throat, and it opens briefly every time you swallow or chew to equalize air pressure. A muscle called the tensor veli palatini is responsible for opening this tube. In a child with a cleft palate, that muscle attaches in the wrong place along the cleft edges instead of the midline, so it can’t pull the tube open effectively.
When the tube stays closed, gases in the middle ear get absorbed by the lining tissue and aren’t replaced. This creates negative pressure that pulls the eardrum inward and eventually draws fluid into the space. The result is a form of temporary hearing loss that, if persistent, can delay speech and language development. On top of that, food and liquid that reflux into the nasal cavity through the cleft can cause chronic irritation around the tube openings, making the problem worse. Ear, nose, and throat specialists monitor these children closely, and many need small tubes placed in the eardrums to keep the middle ear ventilated.
Speech Development
The palate plays a central role in speech. It separates the mouth from the nasal cavity, and during most speech sounds, the soft palate lifts to seal off the nose so that air is directed entirely through the mouth. When the palate has a gap, or even after surgical repair if the palate is too short or doesn’t move well enough, air escapes through the nose during speech. This is called velopharyngeal insufficiency, and it gives speech a nasal quality while making certain consonants hard to produce clearly.
Speech-language specialists begin monitoring children with clefts well before they start talking, tracking babbling patterns and early sound development. Many children achieve typical speech after palate repair and targeted therapy, though some need a secondary surgery to improve the seal between the mouth and nose.
Treatment Timeline
Cleft repair follows a staged approach that aligns with a child’s growth:
- Lip repair: typically performed between 3 and 5 months of age.
- Palate repair: usually between 10 and 14 months, timed to close the gap before the child begins forming words, while also accounting for airway size and overall development.
- Bone grafting: if the cleft extended through the gum line, a bone graft fills the gap in the upper jaw, usually between ages 8 and 12 when the adult canine teeth are preparing to come in.
Beyond these primary surgeries, many children need orthodontic work to align teeth that come in crowded or rotated near the cleft site. Some will have additional procedures in adolescence to refine the appearance of the lip or nose. The full course of treatment can stretch into the late teens, which is why cleft care is managed by a coordinated team that includes surgeons, orthodontists, speech-language specialists, ear-nose-throat doctors, and others who follow the child from infancy through young adulthood.
Prevention
Folic acid, the B vitamin recommended to prevent spinal cord defects, also appears to reduce cleft risk. The standard recommendation for all women of childbearing age is 400 micrograms daily, started before conception and continued through the first 12 weeks of pregnancy. Higher doses, around 5 to 6 milligrams, have shown some ability to prevent clefts in families with a history of the condition, though there is no universally agreed-upon dose specific to cleft prevention.
Avoiding smoking during pregnancy and managing pre-existing diabetes before conceiving are two of the most actionable steps. Because most nonsyndromic clefts involve complex interactions between multiple genes and the environment, there is no way to eliminate the risk entirely, but these measures meaningfully lower it.
Global Trends
Worldwide, the number of new cleft cases dropped from roughly 244,000 in 1990 to about 183,000 in 2021. The burden, however, is not evenly distributed. Regions with fewer healthcare resources carry the heaviest impact: in 2021, the disability rate in low-resource areas was nearly four times higher than in wealthier regions, with Central Asia and the Horn of Africa identified as particular hotspots. Much of this gap comes down to access to surgical care. In well-resourced settings, cleft repair is routine and outcomes are excellent. In areas where surgical teams and follow-up care are scarce, untreated clefts lead to ongoing difficulties with eating, speaking, hearing, and social participation.