Our study found that the prevalence of CDH was 1.82 per 10,000 births and showed an increasing trend over time. Higher prevalence rates were observed among male fetuses, older mothers, and mothers residing in urban areas, particularly in the eastern and central regions. Additionally, infants with associated CDH had a higher risk of premature birth and perinatal death compared to those with isolated CDH.

The prevalence rate of overall CDH is lower than rates reported in studies from the United States [7], France [22], Australia [9], Finland [23], Croatia [24], Sweden [25], and other European countries [1]. One possible explanation for the difference between our study and others is that our surveillance is hospital-based, while others are population-based. However, when compared to other hospital-based surveillance programs in Argentina, Cuba, Japan, and Saudi Arabia, our prevalence is still lower [21, 26]. Our study also revealed a lower prevalence in both isolated (1.13/10,000 births) and associated cases (0.69/10,000 births) [1, 6]. Factors such as birth definition, racial characteristics, and time range may contribute to these differences in prevalence rates.

An increasing trend in the prevalence of CDH was observed during the study period. However, trends in CDH prevalence varied across different countries and regions. For example, no change was seen in California from 1989 to 1997 [6] or in the United States from 1995 to 2002 [7]. In contrast, our analysis showed an upward trend in CDH prevalence over time, consistent with the studies conducted in the Middle East, Europe, North America, Central America, and South America [1, 21]. Our upward trend was even more significant, with an average annual percent change of 7.32%, compared to 0.47% in the aforementioned regions [21]. The rising trend of CDH prevalence in China may be attributed to improvements in prenatal diagnosis, including better and more accessible ultrasonography. Changes in maternal environmental exposures and other factors associated with CDH may also contribute to the increasing trend.

Our study showed a higher risk of CDH among older mothers, consistent with previous studies [6, 7, 27, 28], which was also comparable to studies that found no association or observed a slight, non-significant increase in prevalence among older maternal age groups [1, 6, 29]. Furthermore, our finding that males are at an approximately 20% higher risk than females for developing CDH is in general agreement with previous studies [6, 7, 13, 30]. In our study, higher prevalence rates were found in the eastern and central regions and in urban areas, suggesting a possible role for environmental factors in the pathogenesis of CDH.

CDH can be diagnosed prenatally or postnatally. The percentage of patients with CDHs diagnosed prenatally by ultrasound has significantly increased over the last 20 years, from 15% to 50%–75% [31]. In our study, 87.4% of the overall CDH cases were diagnosed prenatally, close to the 84.1% reported in other findings [32]. This is likely due to advances in ultrasonic diagnosis technology. Consistent with previous studies [1, 22, 33, 34], we found that the prenatal detection rate was higher for the non-isolated CDH cases than for the isolated cases. This may be because non-isolated CDH can be detected earlier by prenatal ultrasound [22, 33]. Our study and others confirm that there is large national variation in the prenatal detection rate of CDH due to differences in policies regarding antenatal routine ultrasound screening [1]. Associated anomalies may also contribute to the prenatal detection of CDH fetuses.

CDH is known to be associated with other structural anomalies and chromosome abnormalities, with the proportion of associated anomalies ranging from 28.2% to 85.3% [1, 6, 9, 13]. The large range of changes may be due to the differences in the CDH case confirmation and data sources. In our analysis, approximately one-third of CDH patients had associated anomalies, consistent with other studies [3, 13, 21, 31, 35]. Specifically, we observed the highest frequency of co-occurring cardiovascular anomalies, followed by musculoskeletal anomalies and nervous system malformations, which are the same as those of previous investigations [6]. Accompanying the high incidence of congenital heart disease in CDH is increasing evidence of fetal ventricular hypoplasia, characterized by a narrowing and elongation of the left ventricle [36,37,38,39]. The development of fetal left ventricle hypoplasia is likely multifactorial, secondary to direct mechanical compression of the left ventricle by the herniated abdominal viscera and flow-related mechanisms [40]. Left ventricle hypoplasia could be a risk factor for early postnatal ventricular dysfunction, increasingly recognized as a contributor to CDH pathophysiology and outcome [41].

Mortality rates for CDH patients vary considerably in the literature. Our study found an overall perinatal mortality rate of 70.3%, higher than the mortality of 42%–68% reported in other studies [9, 42, 43]. Differences in measuring mortality among CDH patients make it difficult to accurately evaluate variations between studies, which may be due to the presence of “hidden mortality” [42, 44]. “Hidden mortality” refers to the exclusion of intrauterine deaths and induced terminations from institution-based studies. Therefore, recently reported increases in survival rates should be interpreted with caution. Our study found that the mortality rate of stillbirths and terminations was 62.2%, which partially accounted for the “hidden mortality”. Despite accounting for “hidden deaths” in our mortality calculations, our study still reported a higher perinatal mortality rate compared to the literature [22, 42, 45]. This variation may be attributed to differences in the type of registry (national hospital-based vs. regional population-based) [22], the time period considered (perinatal vs. neonatal) [42], and the populations studied (all births vs. postmortems) [45]. Because 29.8% of CDH cases survived the perinatal period, we were unable to obtain information on subsequent treatment. However, other studies have confirmed that live births with CDH almost always receive treatment [24].

The rate of preterm delivery in our study appeared to be higher than that reported by another registry [7, 46]. CDH cases with a gestational age of less than 37 weeks were classified as premature, regardless of whether they resulted in live births, stillbirths, or terminations in our study. After excluding cases of pregnancy termination, the rate in our study was slightly lower than that reported in other studies [7, 46], although the difference was not statistically significant. As such, we hypothesized that the high rate of preterm birth observed in our study may be partly attributable to the high rate of pregnancy termination. In agreement with the findings of Shanmugam et al. [46], our study found that CDH cases with associated anomalies were more likely to result in premature delivery than isolated CDH cases. Similarly, when terminations were excluded from our analysis, a higher proportion of CDH cases with associated anomalies were born prematurely compared to isolated cases.

Infants with associated CDH were at a higher risk of perinatal death (80.1%) compared with those affected by isolated CDH (63.2%), consistent with previous reports [1, 22, 43]. In addition to cardiovascular system defects, there were more musculoskeletal diseases and neurological diseases among deceased patients, indicating that multiple malformations, especially circulatory, musculoskeletal, and central nervous system anomalies, are important factors in perinatal mortality.

Using 13 years of surveillance data and covering 24 million births, this study represents the most extensive investigation to date on the birth prevalence and time trend of CDH in the Chinese population. The wide geographical coverage, consistent case ascertainment methods, and adjustment for several characteristics ensure reliable estimates of the prevalence of CDH and the potential relationship between the maternal and infant characteristics and risk for CDH.

This study has several limitations. Firstly, the observed CDH prevalence may be underestimated due to hospital-based samples with a short monitoring period and incomplete population coverage. Secondly, information on chromosomal anomalies and syndromes for some CDH was unavailable due to limited chromosomal testing and syndromic case ascertainment in some member hospitals. Finally, CDH cases could not be classified based on the anatomical position of the defect, as the hernia types were not included in the routine data collection.

In conclusion, our study found that the Chinese population has a relatively low risk for CDH, but challenges remain. Cardiovascular anomalies are most commonly associated with CDH. The increasing trend in prevalence, demographic risk factors, and high perinatal mortality rate highlight the need for further research on the etiology, epidemiology, and clinical management of CDH in the contemporary Chinese population.