# A 40-Year Regional Study of Cleft Lip and/or Palate Incidence in Tokai, Japan

## TL;DR

A 43-year study in Japan's Tokai region found that the incidence of cleft lip and/or palate remained stable despite demographic changes.

## Contribution

This paper provides a long-term regional epidemiological analysis of CL/P in Japan, highlighting consistent incidence rates over four decades.

## Key findings

- CL/P incidence remained stable at 10-20 cases per 10,000 live births from 1981 to 2023.
- Sex ratios for cleft types shifted after 2004, with males becoming more prevalent for isolated cleft palate.
- No significant increase in CL/P or other major congenital anomalies was observed despite rising maternal age and social changes.

## Abstract

Objective: Cleft lip and/or palate (CL/P) is among the most common congenital craniofacial anomalies worldwide, with reported incidences ranging from approximately 1 in 500 to 2,500 live births, depending on the geographic region and ethnic background. While genetic and environmental factors contribute to its etiology, long-term regional surveillance is essential to detect trends and identify risk factors. This study investigates the epidemiological characteristics of CL/P in the Tokai region of Japan over a 43-year period (1981-2023).

Methods: Since 1981, the Cleft Lip and Palate Center at Aichi Gakuin University Dental Hospital has been conducting an annual population-based monitoring survey involving all obstetric facilities in Aichi, Gifu, and Mie prefectures. Mailed questionnaires captured data on total live births, presence and types of congenital anomalies, CL/P occurrence and classification, sex, and any associated anomalies. Trends in annual incidence, cleft type distributions, sex ratios, and comorbid anomaly prevalence were analyzed.

Results: Over the 43-year period, the incidence of CL/P remained stable, ranging from 10 to 20 cases per 10,000 live births per year, with no statistically significant year-by-year variations. Cleft lip (CL) and cleft lip with palate (CLP) were more frequent in males, whereas isolated cleft palate (CP) was historically more common in females. After 2004, CP showed a reversal of the sex ratio, with more male cases than female (p < 0.001). Despite rising maternal age and social changes, no significant trend toward increasing CL/P incidence was observed. Similarly, the prevalence of other major congenital anomalies (e.g., cardiac, limb, chromosomal disorders), as reported through the annual regional survey beginning in 2009, remained stable through 2023.

Conclusion: This long-term regional surveillance study demonstrates a stable incidence of CL/P in the Tokai region in spite of demographic shifts, such as declining birth rates and rising maternal age. These findings emphasize the value of sustained, regionally based congenital anomaly monitoring systems in guiding health policy, perinatal counseling, and genetic risk assessment.