Nulliparous teenagers and preterm birth in California.

BACKGROUND: Young maternal age is one of the numerous risk factors for delivery before 37 weeks of gestation, yet the mechanisms are unclear. The purpose of the current study was to investigate the association between teenagers and the risk of preterm birth (PTB) in a large and recent cohort study. METHODS: We conducted a population-based retrospective cohort study using 2007-2011 California birth certificate records linked with hospital discharge indices and United States census data for nulliparous 13-20 year olds who gave birth to singletons. Maternal age was examined categorically at 1 year intervals. PTB was defined as delivery at <37 weeks of gestation with further distinction between <32 and 32-36 weeks, and between spontaneous and medically indicated deliveries. Adjusted multivariable logistic regression was used to estimate odds ratios (OR) for PTB. RESULTS: The prevalence of PTB was highest among the youngest (13 year olds, 14.5%) and lowest among the oldest (20 year olds, 6.7%). After adjusting for maternal and paternal race/ethnicity, paternal age, initiation of prenatal care, source of payment, pre-pregnancy body-mass-index (BMI), height, smoking, and poverty; young mothers of ages 13, 14, 15, and 16 years had increased odds for spontaneous PTB at <32 weeks [OR (CI): 3.76 (1.83-7.75), 1.65 (1.10-2.48), 1.55 (1.24-1.93), 1.19 (1.00-1.42), respectively] compared to 20 year olds. All teenagers, excluding 19 year olds, had elevated odds of spontaneous PTB at 32-36 weeks. CONCLUSIONS: Nulliparous teenagers were at increased risk for spontaneous PTB, especially those 16 years or younger. Medically indicated PTB was not associated with young age.

Effects of race/ethnicity and BMI on the association between height and risk for spontaneous preterm birth.

OBJECTIVE: Short height and obesity have each been associated with increased risk for preterm birth (PTB). However, the effect of short height on PTB risk, across different race/ethnicities and body mass index (BMI) categories, has not been studied. Our objective was to determine the influence of maternal height on the risk for PTB within race/ethnic groups, BMI groups, or adjusted for weight. STUDY DESIGN: All California singleton live births from 2007 through 2010 were included from birth certificate data (vital statistics) linked to hospital discharge data. Prepregnancy BMI (kg/m(2)) was categorized as underweight (<18.5), normal (18.5-24.9), overweight (25.0-29.9), or obese (≥30.0). Maternal race/ethnicity was categorized as: non-Hispanic white, non-Hispanic black, Hispanic, and Asian. Maternal height was classified into 5 categories (shortest, short, middle, tall, tallest) based on racial/ethnic-specific height distributions, with the middle category serving as reference. Poisson regression models were used to estimate relative risks for the association between maternal height and risk of spontaneous PTB (<37 weeks and <32 weeks). Models were stratified on race/ethnicity and BMI. Generalized additive regression models were used to detect nonlinearity of the association. Covariates considered were: maternal age, weight, parity, prenatal care, education, medical payment, previous PTB, gestational and pregestational diabetes, pregestational hypertension, preeclampsia/eclampsia, and smoking. RESULTS: Among 1,655,385 California singleton live births, 5.2% were spontaneous PTB <37 weeks. Short stature (first height category) was associated with increased risk for PTB for non-Hispanic whites and Hispanics across all BMI categories. Among obese women, tall stature (fifth category) was associated with reduced risk for spontaneous PTB for non-Hispanic whites, Asians, and Hispanics. The same pattern of association was seen for height and risk for spontaneous PTB <32 weeks. In the generalized additive regression model plots, short stature was associated with increased risk for spontaneous PTB of <32 and <37 weeks of gestation among whites and Asians. However, this association was not observed for blacks and Hispanics. CONCLUSION: Maternal shorter height is associated with a modest increased risk for spontaneous PTB regardless of BMI. Our results suggest that PTB risk assessment should consider race/ethnicity-specific height with respect to the norm in addition to BMI assessment.

Maternal prepregnancy body mass index and risk of spontaneous preterm birth.

BACKGROUND: Findings from studies examining risk of preterm birth associated with elevated prepregnancy body mass index (BMI) have been inconsistent. METHODS: Within a large population-based cohort, we explored associations between prepregnancy BMI and spontaneous preterm birth across a spectrum of BMI, gestational age, and racial/ethnic categories. We analysed data for 989,687 singleton births in California, 2007-09. Preterm birth was grouped as 20-23, 24-27, 28-31, or 32-36 weeks gestation (compared with 37-41 weeks). BMI was categorised as <18.5 (underweight); 18.5-24.9 (normal); 25.0-29.9 (overweight); 30.0-34.9 (obese I); 35.0-39.9 (obese II); and ≥ 40.0 (obese III). We assessed associations between BMI and spontaneous preterm birth of varying severity among non-Hispanic White, Hispanic, and non-Hispanic Black women. RESULTS: Analyses of mothers without hypertension and diabetes, adjusted for age, education, height, and prenatal care initiation, showed obesity categories I-III to be associated with increased risk of spontaneous preterm birth at 20-23 and 24-27 weeks among those of parity 1 in each race/ethnic group. Relative risks for obese III and preterm birth at 20-23 weeks were 6.29 [95% confidence interval (CI) 3.06, 12.9], 4.34 [95% CI 2.30, 8.16], and 4.45 [95% CI 2.53, 7.82] for non-Hispanic Whites, non-Hispanic Blacks, and Hispanics, respectively. A similar, but lower risk, pattern was observed for women of parity ≥ 2 and preterm birth at 20-23 weeks. Underweight was associated with modest risks for preterm birth at ≥ 24 weeks among women in each racial/ethnic group regardless of parity. CONCLUSIONS: The association between women's prepregnancy BMI and risk of spontaneous preterm birth is complex and is influenced by race/ethnicity, gestational age, and parity.

Risk for spontaneous preterm birth among inter-racial/ethnic couples.

OBJECTIVE: Approximately 10% of US couples are inter-racial/ethnic. Substantial variation in preterm birth (PTB) rates is seen when stratified by race/ethnicity, although most studies focused solely on maternal racial/ethnic demographics. Our aims were to analyze the contribution of paternal in addition to maternal race/ethnicity, and to evaluate risk of spontaneous PTB for previously understudied inter-racial/ethnic couples. METHODS: California singleton live births from 2007 to 2010 were included. Race/ethnicity was determined based on self-report, obtained from birth certificates and defined as African American (AA), Hispanic, Asian, and White. Logistic regression was used to estimate odds ratios of spontaneous PTB at 20-23, 24-31, 32-36 and <37 weeks of gestation, with White-White couples as reference. Results were stratified by previous PTB, pre-gestational and gestational diabetes and hypertension. To investigate the paternal contribution to the risk for any given maternal race/ethnicity we assessed the rates of PTB among inter-racial/ethnic couples compared to the respective same-race couple. Odds ratios were adjusted for maternal age, parity, BMI, prenatal care, payor status, education and smoking. RESULTS: Among 1,664,939 live births, 13% (n = 216,417) were born to inter-racial/ethnic couples. Compared to White-White couples, risk for spontaneous PTB was increased across all inter-racial/ethnic couples with a non-White mother, except when the father was Asian. Patterns of association were similar after stratification by previous PTB, hypertension and diabetes. Paternal race/ethnicity was also a significant risk factor for PTB. CONCLUSIONS: Increased risks for spontaneous PTB were seen in most inter-racial/ethnic couple groupings. In addition to maternal race/ethnicity, paternal race/ethnicity was a significant risk factor in many inter-racial/ethnic couplings. Identifying such different risk profiles based on both maternal and paternal race/ethnicity may offer new lines of research inquiry for the underlying etiologies of PTB.

Could genetic polymorphisms related to oxidative stress modulate effects of heavy metals for risk of human preterm birth?

Human preterm birth (PTB) is a complex medical outcome influenced by a combination of genetic and environmental factors. Research on the causative factors of PTB has mostly focused on demographic, socio-behavioral and environmental risk factors. Recent studies turn the spotlight on the effects of heavy metals exposure on adverse pregnancy outcomes. Here we present and evaluate the hypothesis that heavy metals may cause PTB through oxidative stress, and that this effect may be modified by polymorphisms in genes related to oxidative stress. Indeed, accumulating data suggest that the risk of PTB is correlated with polymorphisms in genes involved in detoxification, oxidative stress and lipid metabolism. These and other polymorphisms have independently been associated with susceptibility to the adverse effects of heavy metals.

Interpregnancy interval and obstetrical complications.

Obstetricians are often presented with questions regarding the optimal interpregnancy interval (IPI). Short IPI has been associated with adverse perinatal and maternal outcomes, ranging from preterm birth and low birth weight to neonatal and maternal morbidity and mortality. Long IPI has in turn been associated with increased risk for preeclampsia and labor dystocia. In this review, we discuss the data regarding these associations along with recent studies revealing associations of short IPI with birth defects, schizophrenia, and autism. The optimal IPI may vary for different subgroups. We discuss the consequences of short IPI in women with a prior cesarean section, in particular the increased risk for uterine rupture and the considerations regarding a trial of labor in this subgroup. We review studies examining the interaction between short IPI and advanced maternal age and discuss the risk-benefit assessment for these women. Finally, we turn our attention to women after a stillbirth or an abortion, who often desire to conceive again with minimal delay. We discuss studies speaking in favor of a shorter IPI in this group. The accumulated data allow for the reevaluation of current IPI recommendations and management guidelines for women in general and among subpopulations with special circumstances. In particular, we suggest lowering the current minimal IPI recommendation to only 18 months (vs 24 months according to the latest World Health Organization recommendations), with even shorter recommended minimal IPI for women of advanced age and those who conceive after a spontaneous or induced abortion.