Comparative analysis of necrotizing enterocolitis in preterm infants born in Japan and born to mothers of Japanese ethnicity in California

Infants born in Japan are reported to have a low incidence of necrotizing enterocolitis (NEC) among countries, and these differences remained significant after adjusting for common clinical factors. To investigate the impact of ethnic background, we compared the incidence of NEC between infants born in Japan and those born to mothers of Japanese ethnicity in California. Preterm infants born between 2008 and 2019 at 22-29 weeks of gestational age were analyzed retrospectively. Four groups were analyzed: infants born in Japan (JP), infants born in California to mothers born in Japan (JP-J), infants born in California to mothers with Japanese ethnicity but born in the United States or another country (JP-CA), and a comparison group of infants born in California to non-Hispanic White mothers (NHW-CA). Each cohort consisted of 52,049, 115, 226, and 12,275 infants, respectively. Unadjusted NEC incidences were significantly lower in JP compared to the other three cohorts (1.7% JP, 4.5% JP-J, 4.6% JP-CA, and 3.3% NHW-CA, respectively; p < 0.01). After adjusting for confounding factors, odds ratios for NEC in JP vs. JP-J, JP-CA, and NHW-CA were 3.04 (1.18-7.80), 2.89 (1.45-5.75), and 1.96 (1.56-2.47), respectively. This study suggests that differences in NEC incidence in Japan are not explained by ethnicity.Clinical trial regstration number: Registration numbers is UMIN000006961 ( https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000008217 ) for the Neonatal Research Network of Japan. However, the the California Perinatal Quality Care Collaborative (CPQCC) aims only to assess neonatal outcomes for the purpose of quality assessment and improvement. So, no clinical trial number is available. Please refer to the web site https://www.cpqcc.org/ .