Cleft lip is one of the most common birth defects worldwide. In the United States, about 1 in every 1,031 babies is born with a cleft lip, with or without an accompanying cleft palate. That translates to roughly 4,000 affected births per year in the U.S. alone. The rate varies significantly depending on ethnicity, sex, and certain prenatal exposures.
Prevalence by Ethnicity
Not all populations face the same risk. A large U.S. study published in the Journal of Clinical Medicine found that Native American, Native Hawaiian, Alaskan Native, and Pacific Islander populations had the highest rate of oral clefts: about 33 per 10,000 live births. Asian Americans were close behind at roughly 27.5 per 10,000. White Americans had a rate of about 24.4 per 10,000, while Black Americans had the lowest rate at approximately 13 per 10,000.
These differences have been consistent across decades of research and are thought to reflect a combination of genetic factors that vary between populations, though the specific genes involved are still being mapped.
Sex Differences
Cleft lip (with or without cleft palate) is roughly twice as common in males as in females. This 2:1 ratio holds in most studied populations. Interestingly, the male excess becomes more pronounced with more severe clefts. If the cleft is relatively mild, the gap between boys and girls narrows.
Cleft palate alone, without any lip involvement, shows the opposite pattern: it’s more common in girls. Researchers don’t fully understand why sex influences the type of cleft, but it likely relates to differences in the timing of facial development between male and female embryos.
Risk Factors That Increase the Odds
Most cleft lips result from a combination of genetic susceptibility and environmental exposures during early pregnancy, when the face is forming (roughly weeks 6 through 10). No single cause explains the majority of cases, but several factors are well established.
Smoking during pregnancy is one of the strongest modifiable risk factors. Mothers who smoke are about 1.6 times more likely to have a baby with cleft lip (with or without cleft palate) and twice as likely to have a baby with cleft palate alone, compared to nonsmokers. Maternal diabetes, certain anti-seizure medications, and folic acid deficiency have also been linked to higher risk, though the exact increase varies by study.
Alcohol use during the first trimester and obesity before pregnancy have both appeared as contributing factors in large population studies, though their individual effect sizes are smaller than smoking.
Genetic and Family Recurrence Risk
Cleft lip does run in families, but the inheritance pattern is complex. It’s not a single-gene condition like cystic fibrosis. Instead, multiple genes interact with environmental triggers.
If two parents without clefts have one baby born with a cleft, the chance of a second child also having a cleft ranges from 2 to 8 percent. If one parent has a cleft but none of their children do, the risk for any future child is about 4 to 6 percent. When both a parent and a child are affected, the risk for subsequent children climbs higher still. For context, the baseline risk in the general population is about 0.1 percent, so even a 2 percent risk represents a roughly 20-fold increase over average.
Prenatal Detection
Cleft lip can sometimes be spotted on a routine ultrasound, typically the anatomy scan performed around 18 to 20 weeks of pregnancy. However, detection rates are lower than many parents expect. Older data suggested that only 20 to 30 percent of all oral clefts were caught before birth. More recent studies using higher-resolution imaging have pushed that figure closer to 40 percent, though results vary widely between hospitals and technicians.
Cleft lip is easier to detect on ultrasound than cleft palate alone, because the lip is visible on the baby’s face in profile or frontal views. Isolated cleft palate, hidden inside the mouth, is frequently missed until after delivery. When a cleft lip is detected prenatally, about half are identified before 20 weeks, a third between 21 and 24 weeks, and the remainder later in pregnancy.
What Happens After Birth
Cleft lip is typically repaired surgically between 3 and 6 months of age. The surgery closes the gap in the upper lip and reshapes the nose if needed. If a cleft palate is also present, that repair usually follows later, often between 9 and 14 months. Most children with cleft lip go through a series of follow-up visits with a team that may include a surgeon, speech therapist, orthodontist, and audiologist, because clefts can affect feeding, speech development, ear drainage, and tooth alignment.
Outcomes have improved dramatically over the past several decades. With modern surgical techniques, most children who undergo cleft lip repair in infancy have minimal visible scarring by the time they reach school age. Some need additional procedures as they grow, particularly if the cleft extended into the gum line or palate, but the majority reach adulthood with normal speech and appearance.