Maternal Smoking during Pregnancy and Necrotizing Enterocolitis-associated Infant Mortality in Preterm Babies

National Trends in Preterm Infant Mortality in the United States by Race and Socioeconomic Status, 1995-2020

Importance

Inequalities in preterm infant mortality exist between population subgroups within the United States.

Objective

To characterize trends in preterm infant mortality by maternal race and socioeconomic status to assess how inequalities in preterm mortality rates have changed over time.

Design, Setting, and Participants

This was a retrospective longitudinal descriptive study using the US National Center for Health Statistics birth infant/death data set for 12 256 303 preterm infant births over 26 years, between 1995 and 2020. Data were analyzed from December 2022 to March 2023.

Exposures

Maternal characteristics including race, smoking status, educational attainment, antenatal care, and insurance status were used as reported on an infant's US birth certificate.

Main Outcomes and Measures

Preterm infant mortality rate was calculated for each year from 1995 to 2020 for all subgroups, with a trend regression coefficient calculated to describe the rate of change in preterm mortality.

Results

The average US preterm infant mortality rate (IMR) decreased from 33.71 (95% CI, 33.71 to 34.04) per 1000 preterm births per year between 1995-1997, to 23.32 (95% CI, 23.05 to 23.58) between 2018-2020. Black non-Hispanic infants were more likely to die following preterm births than White non-Hispanic infants (IMR, 31.09; 95% CI, 30.44 to 31.74, vs 21.81; 95% CI, 21.43 to 22.18, in 2018-2020); however, once born, extremely prematurely Black and Hispanic infants had a narrow survival advantage (IMR rate ratio, 0.87; 95% CI, 0.84 to 0.91, in 2018-2020). The rate of decrease in preterm IMR was higher in Black infants (-0.015) than in White (-0.013) and Hispanic infants (-0.010); however, the relative risk of preterm IMR among Black infants compared with White infants remained the same between 1995-1997 vs 2018-2020 (relative risk, 1.40; 95% CI, 1.38 to 1.44, vs 1.43; 95% CI, 1.39 to 1.46). The rate of decrease in preterm IMR was higher in nonsmokers compared with smokers (-0.015 vs -0.010, respectively), in those with high levels of education compared with those with intermediate or low (-0.016 vs - 0.010 or -0.011, respectively), and in those who had received adequate antenatal care compared with those who did not (-0.014 vs -0.012 for intermediate and -0.013 for inadequate antenatal care). Over time, the relative risk of preterm mortality widened within each of these subgroups.

Conclusions and Relevance

This study found that between 1995 and 2020, US preterm infant mortality improved among all categories of prematurity. Inequalities in preterm infant mortality based on maternal race and ethnicity have remained constant while socioeconomic disparities have widened over time.

Impact of maternal factors, environmental factors, and race on necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a complex disease with a multifactorial etiology. As the leading cause of intestinal morbidity and mortality among premature infants, many resources are being dedicated to neonatal care and molecular targets in the newborn intestine. However, NEC is heavily influenced by maternal and perinatal factors as well. Given its nature, preventive approaches to NEC are more likely to improve outcomes than new treatment strategies. Therefore, this review focuses on maternal, environmental, and racial factors associated with the development of NEC, with an emphasis on those that may be modifiable to decrease the incidence of the disease.

Developmental 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure of either parent enhances the risk of necrotizing enterocolitis in neonatal mice

BACKGROUND

Necrotizing enterocolitis (NEC) is a rare, but potentially fatal intestinal inflammatory condition most often arising in premature infants. Infants provided formula are also at greater risk of developing this disease. Although the majority of formula-fed, preterm infants do not develop NEC, up to 30% of infants with the disease do not survive. Thus, identifying additional, currently unrecognized factors, which may predispose a specific infant to NEC development would be a significant clinical advancement. In this regard, we have previously reported that offspring of female or male mice with a history of developmental exposure to the environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exhibit altered sensitivity to inflammatory challenges and are frequently born premature. Herein, we examined the possibility that, compared to unexposed mice (F1_NONE ), developmental TCDD exposure of either parent (maternal, F1M_TCDD , or paternal, F1P_TCDD ) would enhance the risk of NEC in offspring (F2_TCDD mice) in association with supplemental formula feeding.

METHODS

Beginning on postnatal day 7, all neonates were randomized to maternal milk only or maternal milk with up to 20 supplemental formula feedings. All pups remained with the Dams and were additionally allowed to nurse ad libitum.

RESULTS

Formula-fed F2_NONE pups rarely developed NEC while this disease was common in formula-fed F2M_TCDD and F2P_TCDD mice. Unexpectedly, 50% of F2M_TCDD pups that were not provided supplemental formula also developed NEC.

CONCLUSIONS

Our studies provide evidence that a history of parental TCDD exposure enhances the risk of NEC in offspring and suggest exposure to environmental immunotoxicants such as TCDD may also contribute to this inflammatory disease in humans.

Altered Cortical Brain Structure and Increased Risk for Disease Seen Decades After Perinatal Exposure to Maternal Smoking: A Study of 9000 Adults in the UK Biobank

Secondhand smoke exposure is a major public health risk that is especially harmful to the developing brain, but it is unclear if early exposure affects brain structure during middle age and older adulthood. Here we analyzed brain MRI data from the UK Biobank in a population-based sample of individuals (ages 44-80) who were exposed (n = 2510) or unexposed (n = 6079) to smoking around birth. We used robust statistical models, including quantile regressions, to test the effect of perinatal smoke exposure (PSE) on cortical surface area (SA), thickness, and subcortical volumes. We hypothesized that PSE would be associated with cortical disruption in primary sensory areas compared to unexposed (PSE-) adults. After adjusting for multiple comparisons, SA was significantly lower in the pericalcarine (PCAL), inferior parietal (IPL), and regions of the temporal and frontal cortex of PSE+ adults; these abnormalities were associated with increased risk for several diseases, including circulatory and endocrine conditions. Sensitivity analyses conducted in a hold-out group of healthy participants (exposed, n = 109, unexposed, n = 315) replicated the effect of PSE on SA in the PCAL and IPL. Collectively our results show a negative, long term effect of PSE on sensory cortices that may increase risk for disease later in life.

Intestinal IMINO transporter SIT1 is not expressed in human newborns

The expression of amino acid transporters in small intestine epithelia of human newborns has not been studied yet. It is further not known whether the maturation of imino acid (proline) transport is delayed as in the kidney proximal tubule. The possibility to obtain small intestinal tissue from patients undergoing surgery for jejunal or ileal atresia during their first days after birth was used to address these questions. As control, adult terminal ileum tissue was sampled during routine endoscopies. Gene expression of luminal imino and amino acid transporter SIT1 (SLC6A20) was approximately threefold lower in newborns versus adults. mRNA levels of all other luminal and basolateral amino acid transporters and accessory proteins tested were similar in newborn mucosa compared with adults. At the protein level, the major luminal neutral amino acid transporter B⁰AT1 (SLC6A19) and its accessory protein angiotensin-converting enzyme 2 were shown by immunofluorescence to be expressed similarly in newborns and in adults. SIT1 protein was not detectable in the small intestine of human newborns, in contrast to adults. The morphology of newborn intestinal mucosa proximal and distal to the obstruction was generally normal, but a decreased proliferation rate was visualized distally of the atresia by lower levels of the mitosis marker K_i-67. The mRNA level of the 13 tested amino acid transporters and accessory proteins was nonetheless similar, suggesting that the intestinal obstruction and interruption of amniotic fluid passage through the small intestinal lumen did not affect amino acid transporter expression. NEW & NOTEWORTHY System IMINO transporter SIT1 is not expressed in the small intestine of human newborns. This new finding resembles the situation in the proximal kidney tubule leading to iminoglycinuria. Lack of amniotic fluid passage in small intestinal atresia does not affect amino acid transporter expression distal to intestinal occlusion.