Declines in Pregnancies among U.S. Adolescents from 2007 to 2017: Behavioral Contributors to the Trend.

STUDY OBJECTIVES: Adolescent pregnancies and births in the United States have undergone dramatic declines in recent decades. We aimed to estimate the contribution of changes in 3 proximal behaviors to these declines among 14- to 18-year-olds for 2007-2017: 1) delays in age at first sexual intercourse, 2) declines in number of sexual partners, and 3) changes in contraceptive use, particularly uptake of long-acting reversible contraception (LARC). DESIGN: We adapted an existing iterative dynamic population model and parameterized it using 6 waves of the Centers for Disease Control and Prevention's Youth Risk Behavior Survey. We compared pregnancies from observed behavioral trends with counterfactual scenarios that assumed constant behaviors over the decade. We calculated outcomes by cause, year, and age. RESULTS: We found that changes in these behaviors could explain pregnancy reductions of 496,200, 78,500, and 40,700 over the decade, respectively, with total medical and societal cost savings of $9.71 billion, $1.54 billion, and $796 million. LARC adoption, particularly among 18-year-olds, could explain much of the improvement from contraception use. The 3 factors together did not fully explain observed birth declines; adding a 50% decline in sex acts per partner did. CONCLUSIONS: Delays in first sexual intercourse contributed the most to declining births over this decade, although all behaviors considered had major effects. Differences from earlier models could result from differences in years and ages covered. Evidence-based teen pregnancy prevention programs, including comprehensive sex education, youth-friendly reproductive health services, and parental and community support, can continue to address these drivers and reduce teen pregnancy.

Functional characterization of the water-soluble organic carbon of size-fractionated aerosol in the southern Mississippi Valley.

The chemical content of water-soluble organic carbon (WSOC) as a function of particle size was characterized in Little Rock, Arkansas in winter and spring 2013. The objectives of this study were to (i) compare the functional characteristics of coarse, fine and ultrafine WSOC and (ii) reconcile the sources of WSOC for periods when carbonaceous aerosol was the most abundant particulate component. The WSOC accounted for 5 % of particle mass for particles with δp > 0.96 µm and 10 % of particle mass for particles with δp < 0.96 µm. Non-exchangeable aliphatic (H-C), unsaturated aliphatic (H-C-C=), oxygenated saturated aliphatic (H-C-O), acetalic (O-CH-O) and aromatic (Ar-H) protons were determined by proton nuclear magnetic resonance (1H-NMR). The total non-exchangeable organic hydrogen concentrations varied from 4.1 ± 0.1 nmol m-3 for particles with 1.5 < δp < 3.0 µm to 73.9 ± 12.3 nmol m-3 for particles with δp < 0.49 µm. The molar H/C ratios varied from 0.48 ± 0.05 to 0.92 ± 0.09, which were comparable to those observed for combustion-related organic aerosol. The R-H was the most abundant group, representing about 45 % of measured total non-exchangeable organic hydrogen concentrations, followed by H-C-O (27 %) and H-C-C= (26 %). Levoglucosan, amines, ammonium and methanesulfonate were identified in NMR fingerprints of fine particles. Sucrose, fructose, glucose, formate and acetate were associated with coarse particles. These qualitative differences of 1H-NMR profiles for different particle sizes indicated the possible contribution of biological aerosols and a mixture of aliphatic and oxygenated compounds from biomass burning and traffic exhausts. The concurrent presence of ammonium and amines also suggested the presence of ammonium/aminium nitrate and sulfate secondary aerosol. The size-dependent origin of WSOC was further corroborated by the increasing δ13C abundance from -26.81 ± 0.18 ‰ for the smallest particles to -25.93 ± 0.31 ‰ for the largest particles and the relative distribution of the functional groups as compared to those previously observed for marine, biomass burning and secondary organic aerosol. The latter also allowed for the differentiation of urban combustion-related aerosol and biological particles. The five types of organic hydrogen accounted for the majority of WSOC for particles with δp > 3.0 µm and δp < 0.96 µm.