Racial disparity in fetal growth inhibition among singletons and multiples

Understanding Racial Disparities of Preterm Birth Through the Placenta

The racial disparity associated with preterm birth is a public health concern in the United States. The placenta is the principal metabolic, respiratory, and endocrine organ of the fetus and a key route by which environmental exposures are transmitted from mother to offspring. Available at every delivery, it may serve as a marker of differences in prenatal exposures that manifest differently by race. Recently, we described differences in placental pathology between African-American and White preterm births: the prevalence of chronic inflammation was higher among African-American women's placentas compared with those of White women. Similarly, racial differences have been shown in placental malperfusion and placental weight. Social determinants such as poverty and stress from discrimination have been implicated in racial disparities in preterm birth. To date, however, the underlying biological mechanisms, whether through inflammatory, oxidative stress, or other pathways involving epigenetic programming, remain largely unknown. The placenta, complemented by maternal and umbilical cord blood biomarkers, may provide important information on the perinatal environment that explains the origins of racial disparities in preterm birth rates and subsequent health outcomes. This article reviews existing literature and current research gaps. Opportunities are discussed for future placental research that may reveal novel mechanisms leading to the development of new approaches in the prevention and management of preterm birth and its outcomes.

Cross sectional study in China: fetal gender has adverse perinatal outcomes in mainland China

Background

The association between fetal gender and pregnancy outcomes has been thoroughly demonstrated in western populations. However, this association has not been thoroughly documented in China. The primary objective of the present study is to determine whether the association of adverse pregnancy and labour outcomes with male fetuses applies to the Chinese population.

Methods

This cross-sectional hospital-based retrospective survey collected data from thirty-nine hospitals in 2011 in mainland China. A total of 109,722 women with singleton pregnancy who delivered after 28 weeks of gestation were included.

Results

Of these pregnancies, the male-to-female sex ratio was 1.2. The rates of preterm birth (7.3% for males, 6.5% for females) and fetal macrosomia (8.3% for males, 5.1% for females) were higher for male newborns, whereas fetal growth restriction (8.0% for females, 5.4% for males) and malpresentation (4.3% for females, 3.6% for males) were more frequent among female-bearing mothers. A male fetus was associated with an increased incidence of operative vaginal delivery (1.3% for males, 1.1% for females), caesarean delivery (55.0% for males, 52.9% for females), and cephalopelvic disproportion/failure to progress (10.0% for males, 9.2% for female). Male gender was also significantly associated with lower Apgar scores (<7 at 5 min, adjusted odds ratio 1.3, 95% CI 1.0-1.6), as well as a neonatal intensive care unit admission and neonatal death, even after adjustments for confounders (adjusted odds ratio 1.3, 95% CI 1.1-1.5, adjusted odds ratio 1.4, 95% CI 1.1-1.8).

Conclusion

We confirm the existence of obvious neonatal gender bias and adverse outcomes for male fetuses during pregnancy and labour in our population. Further research is required to understand the mechanisms and clinical implications of this phenomenon.

Electronic supplementary material

The online version of this article (doi:10.1186/s12884-014-0372-4) contains supplementary material, which is available to authorized users.

Fetal sex and race modify the predictors of fetal growth

The objective of this study is unknown if fetal sex and race modify the impact of maternal pre-pregnancy body mass index (BMI), and smoking on fetal growth. The authors studied markers of fetal growth in singleton offspring of 8,801 primiparous, normotensive women, enrolled in the Collaborative Perinatal Project. The authors tested for departures from additivity between sex/race and each predictor. The head-to-chest circumference ratio (HCC) decreased more, while birthweight and ponderal index (PI) increased more for each 1 kg/m(2) increase in pre-pregnancy BMI among term females versus males (P = 0.07, P < 0.01 and P = 0.08, interaction respectively). For term offspring of White compared with Black women, smoking independent of "dose" was associated with larger reductions in growth (165 g vs. 68 g reduction in birthweight, P < 0.01, interaction), greater reduction in fetal placental ratio (P < 0.01, interaction), PI (P < 0.01, interaction), and greater increase in HCC (P = 0.02), respectively. The association of BMI and smoking with fetal size appeared to be reversed in term versus preterm infants. Our study provides evidence that the associations of pre-pregnancy BMI and smoking are not constant across sex and race. This finding may be relevant to sex and race differences in neonatal and long term health outcomes.

Population-based reference for birth weight for gestational age in northern China

BACKGROUND

Localized birth weight references for gestational age serve as an essential tool in accurate evaluation of atypical birth outcomes (e.g. small for gestational age) in clinical diagnosis and region-specific epidemiological studies. Such standards are currently not available in Mainland China.

AIMS

To construct up-to-date, sex- and parity-specific birth weight references based on 231,937 births in Taiyuan, China during years 2005-2011.

STUDY DESIGN

Population-based, cross-sectional.

SUBJECTS

Hospital-registered, healthy infants with births dated between 11/01/2005 and 12/31/2011 within Taiyuan area.

OUTCOME MEASURES

Birth weight in grams, and gestational age in complete weeks were calculated using a combination of last-menstrual-date-based estimation and ultrasound examination.

RESULTS

Separate birth weight references are constructed for male and female infants born from primiparous and multiparous mothers. Male infants are found to weigh more than female infants in later gestational ages (appr. weeks 33-42), and infants born to multiparous mother are found to weigh more than infants born to primiparous mothers in later gestational ages (appr. weeks 36-42).

CONCLUSIONS

The Taiyuan birth weight reference curves display similar trends of growth as reference curves from other countries worldwide (Netherlands, Scotland, Australia, Canada, Hong Kong, Korea and Kuwait). However, growth of birth weight for Taiyuan infants tends to be slower compared to European and North American infants regardless of gender, but similar to infants from other Asian countries.

Exploring the health consequences of majority-minority neighborhoods: minority diversity and birthweight among native-born and foreign-born blacks

We examined the association between neighborhood minority diversity and infant birthweight among non-Hispanic US-born black women and foreign-born black women from Sub-Saharan Africa and the non-Spanish speaking Caribbean using 2002-2006 vital statistics birth record data from the state of New Jersey (n = 73,907). We used a standardized entropy score to measure the degree of minority diversity (i.e., non-white multiethnic racial heterogeneity) for each census tract where women lived. We distinguished between four levels of minority diversity, with the highest level representing majority-minority neighborhoods. We estimated mean birthweight for singleton births over this 5-year period using linear regression with robust standard errors to correct for clustering of mothers within census tracts. We found significant differences in mean birthweight by mother's country of origin such that infants of US-born black mothers weighed significantly less than the infants of African and Caribbean immigrants (3130 g vs. 3299 g and 3212 g; p < 0.001). Adjustments for neighborhood deprivation, residential instability, individual-level sociodemographics, maternal health behaviors and conditions, and gestational age did not reduce these origin differences. Minority diversity had a protective effect on black infant health. Women living in low and moderately diverse tracts as well as those in majority-minority neighborhoods had heavier babies (β = 26.5, 29.8 and 61.2, respectively, p < 0.001) on average than women in the least diverse tracts. The results for majority-minority neighborhoods were robust when we controlled for neighborhood- and individual-level covariates.

Small size for gestational age and the risk for infant mortality in the subsequent pregnancy

PURPOSE

To examine the association between small for gestational age (SGA) in the first pregnancy and risk for infant mortality in the second pregnancy.

METHODS

This is a population-based, retrospective cohort study in which we used the Missouri maternally linked cohort dataset for 1978-2005. Analyses were restricted to women who had two singleton pregnancies during the study period. The exposure was SGA in the first pregnancy, whereas the primary outcome was infant mortality in the second pregnancy. Kaplan-Meier Estimate and Cox proportional hazard regression were conducted.

RESULTS

Infant mortality was significantly greater among mothers with previous SGA (P < .01). A persistent association of previous SGA with subsequent infant mortality was observed (adjusted hazard ratio [AHR] 1.35, 95% confidence interval [95% CI] 1.24-1.48). Race-specific data illustrated that black women with a previous SGA birth were 40% more likely to experience infant mortality (AHR 1.40, 95% CI 1.21-1.63) than their counterparts without a history of SGA, but white women with a previous SGA had an increased risk of 31% (AHR 1.31, 95% CI 1.17-1.46).

CONCLUSIONS

Women with previous SGA bear increased risks for subsequent infant mortality, which was greater among black mothers. Hence, SGA plays an important role in the black-white disparity in infant mortality. Women's previous childbearing experiences could serve as important criterion in determining appropriate interconception strategies to improve infant health and survival.

Neighbourhood deprivation and small-for-gestational-age term births in the United States

Residential context has received increased attention as a possible contributing factor to race/ethnic and socio-economic disparities in birth outcomes in the United States. Utilising vital statistics birth record data, this study examined the association between neighbourhood deprivation and the risk of a term small-for-gestational-age (SGA) birth among non-Hispanic whites and non-Hispanic blacks in eight geographical areas. An SGA birth was defined as a newborn weighing <10th percentile of the sex- and parity-specific birthweight distribution for a given gestational week. Multi-level random intercept logistic regression models were employed and statistical tests were performed to examine whether the association between neighbourhood deprivation and SGA varied by race/ethnicity and study site. The risk of term SGA was higher among non-Hispanic blacks (range 10.8-17.5%) than non-Hispanic whites (range 5.1-9.2%) in all areas and it was higher in cities than in suburban locations. In all areas, non-Hispanic blacks lived in more deprived neighbourhoods than non-Hispanic whites. However, the adjusted associations between neighbourhood deprivation and term SGA did not vary significantly by race/ethnicity or study site. The summary fully adjusted pooled odds ratios, indicating the effect of one standard deviation increase in the deprivation score, were 1.15 [95% CI 1.08, 1.22] for non-Hispanic whites and 1.09 [95% CI 1.05, 1.14] for non-Hispanic blacks. Thus, neighbourhood deprivation was weakly associated with term SGA among both non-Hispanic whites and non-Hispanic blacks.

Healthy start program and feto-infant morbidity outcomes: evaluation of program effectiveness

OBJECTIVE

We evaluate the impact of the Healthy Start intervention program on feto-infant morbidity within a community setting.

METHODS

Prospective data from 2002 to 2007 within the ongoing Federally funded Healthy Start intervention project in Central Hillsborough County were merged with corresponding birth outcomes data from the Florida Department of Health. The impact of the project on the following feto-infant morbidity indices was assessed among service recipients: low birth weight (LBW), very low birth weight (VLBW), preterm, very preterm, small for gestational age (SGA) and a composite feto-infant morbidity outcome. Program effectiveness and impact were measured using odds ratios from logistic regression models and number needed to treat (NNT).

RESULTS

The risk for low birth weight (OR = 0.7; 95% CI = 0.5-1.0), preterm (OR = 0.7; 95% CI = 0.5-0.9) and the composite feto-infant morbidity outcome (OR = 0.8; 95% CI = 0.6-0.9) was reduced among service recipients (N = 536) as compared to non-recipients (N = 2,815). A clinically important level of risk reduction was also noted for very low birth weight (OR = 0.5; 95% CI = 0.2-1.1) and very preterm (OR = 0.6; 95% CI = 0.3-1.2) although these did not reach statistical significance. The adjusted NNT was lowest for the composite feto-infant morbidity outcome (18), preterm birth (21) and low birth weight (24), and highest for very preterm (86) and very low birth weight (74) events.

CONCLUSIONS

In a disadvantaged community setting, the Healthy Start intervention program was found to reduce the risk for very low birth weight and preterm births by about one-third.

Obesity subtypes and risk of spontaneous versus medically indicated preterm births in singletons and twins

Using data from the Missouri maternally linked files (1989-1997), the authors examined the association among maternal obesity, obesity subtypes, and spontaneous and medically indicated preterm (<37 weeks) and very preterm (<33 weeks) births in singletons and twins. Adjusted odds ratios were obtained with correction for intracluster correlation. The prevalence of obesity increased by 77% over the study period (p(trend) < 0.001). Obese mothers had a lower risk for spontaneous preterm birth, and this was more pronounced among twins (odds ratio = 0.68, 95% confidence interval: 0.62, 0.75) than singletons (odds ratio = 0.84, 95% confidence interval: 0.82, 0.87). However, this association was present only among obese women who gained less than 0.69 kg/week for singletons and between 0.23 and 0.69 kg/week for twins. By contrast, obese mothers with singleton gestation had about 50% greater odds of medically indicated preterm (odds ratio = 1.46, 95% confidence interval: 1.39, 1.54) and very preterm (odds ratio = 1.49, 95% confidence interval: 1.34, 1.65) births, and the risk increases with ascending severity of obesity (p(trend) < 0.01). For extreme obesity, the risk of medically indicated preterm and very preterm births was almost double that for nonobese women. Similar findings were observed in twins. These data suggest that obesity increases the risk for medically indicated but not spontaneous preterm birth in both singletons and twins.

Ethnic differences in the association of birth weight and blood pressure: the Georgia cardiovascular twin study

BACKGROUND

African Americans (AAs) not only have higher blood-pressure levels, but also an increased risk of low weight at birth, compared with European Americans (EAs). In light of fetal programming theories, it has been suggested that ethnic differences in blood pressure originate in utero. However, most previous studies in biethnic samples have not found a significant inverse association between birth weight and blood pressure in AAs.

METHODS

In 562 EA and 465 AA adolescent twins of the Georgia Cardiovascular Twin Study, we investigated the potential ethnic difference in the association of blood pressure and birth weight, with the ability to control for potential confounding by familial factors.

RESULTS

Blood-pressure levels were significantly higher in AAs compared to EAs, independent of birth weight (P < .01). After adjustment for parental factors and body mass index, the difference in systolic blood pressure per kg birth weight was -1.1 mm Hg (95% confidence interval, -2.7 to 0.48, P = .17) in EAs, and -2.5 mm Hg (95% confidence interval, -4.7 to -0.40, P = .02) in AAs. A significant ethnic interaction was revealed in paired analysis, where the inverse association remained in AAs, but not in EAs. Associations with diastolic blood pressure were generally weaker and nonsignificant.

CONCLUSIONS

We showed that low birth weight was associated with an elevated systolic blood pressure in AAs, independent of familial factors. The results also suggest that the association between birth weight and blood pressure may be more pronounced in AAs in adolescence.

Fetal growth and neonatal mortality in Korea

The fetal growth curve and neonatal mortality rate, based on gestational age and birthweight, are important for identifying groups of high-risk neonates and developing appropriate medical services and health-care programmes. The purpose of this study was to develop a national fetal growth curve for neonates in Korea, and examine the Korean national references for fetal growth and death according to their characteristics. Data of Korean vital statistics linked National Infant Mortality Survey conducted on births in 1999 were used in this study. The total livebirths were 621,764 in 1999, which were grouped into singletons (n = 609,643) and twins (n = 9805) for analysis. Birthweight/gestational age-specific fetal growth curves and neonatal mortality rates were based on 250 g of birthweight and weekly gestational age intervals for each characteristic of the birth. The features of high-risk neonates such as small-for-gestational-age and the limit of viability in Korea were different from those of Western countries. Difference in fetal growth and death was also detected in other characteristics of the fetus (gender and plurality of birth) besides race. The fetal growth curve of males was higher than that of females, and was higher in singleton than in twins. The neonatal mortality rate was higher in males (singleton, 2.6; twin, 23.5) than females (singleton, 2.1; twin, 15.9), and higher in twins (19.8/1000) than in singletons (2.4/1000). However, in neonates with gestational age >29 weeks and birthweight >1000 g, the neonatal mortality rate was lower in twins than in singletons. The limit of viability was gestational age 27 weeks and birthweight 1000 g, which was similar in singletons and twins regardless of gender. To improve the health of neonates in a country, it is imperative to investigate the characteristics of fetal growth and death under the particular circumstances of the country. When risk is defined for neonates account must be taken of differences in race, gender and plurality of birth, as the neonatal mortality rate varies depending on those factors.