ABSTRACT
OBJECTIVE: Teenagers are susceptible to delivering small-for-gestational-age (SGA) infants. Previous studies suggest that maternal growth may contribute, as a result of preferential nutrient partitioning to the mother. We investigated the impact of maternal growth on birthweight in pregnant teenagers in the UK, and examined endocrine mediators of nutrient partitioning. DESIGN: A prospective observational multicentre study, About Teenage Eating, conducted between 2004 and 2007. SETTING: Four hospitals in socially-deprived areas of Manchester and London. POPULATION: A total of 500 pregnant adolescents (14-18 years of age) with a singleton pregnancy were recruited at 10-21 weeks of gestation, with follow-up studies on 368 subjects. A cohort of 80 pregnant adults (25-40 years of age) provided a control group for determining growth. METHODS: Skeletal growth, weight gain and skinfold thickness were measured from first to third trimester, together with maternal levels of micronutrients and metabolic hormones: insulin-like growth factor (IGF) system and leptin. Dietary analyses were performed. MAIN OUTCOME MEASURE: SGA birth. RESULTS: Maternal growth was not associated with SGA birth: growing mothers delivered more large-for-gestational-age infants (OR 2.51; P < 0.05). Growers had greater weight gain (P < 0.001), fat accrual (P < 0.001) and red cell folate concentrations (P < 0.01) than non-growers. Maternal IGF-I (P < 0.01) and leptin (P < 0.001) were positively associated with maternal and fetal growth, whereas IGF-I (P < 0.001) was negatively associated. Teenagers that were underweight at booking or with low weight gain were at greater risk of SGA birth. CONCLUSIONS: Maternal growth was not detrimental to fetal growth in this UK population of teenagers. Greater weight gain and higher concentrations of IGF-I in growing teenagers may provide anabolic drive for maternal and fetal growth.
Subject(s)
Fetal Development/physiology , Infant, Low Birth Weight , Infant, Small for Gestational Age , Pregnancy in Adolescence/physiology , Prenatal Nutritional Physiological Phenomena/physiology , Adolescent , Adult , England/epidemiology , Enzyme-Linked Immunosorbent Assay , Female , Folic Acid/blood , Humans , Infant, Newborn , Insulin-Like Growth Factor Binding Protein 3/metabolism , Insulin-Like Growth Factor I/metabolism , Knee/anatomy & histology , Leptin/metabolism , Micronutrients/blood , Pregnancy , Pregnancy in Adolescence/metabolism , Pregnancy in Adolescence/statistics & numerical data , Prospective Studies , Weight Gain/physiologyABSTRACT
The surface and bulk optical absorption of germanium as a function of resistivity and surface condition has been measured at 10.6 microm using adiabatic laser calorimetry. It was found that with conventional optical polishing {Linde, Al(2)O(3)), up to ~50% of the total absorption in a 1-cm thick sample could be attributed to the surfaces. Subsequent polishing with colloidal silica (Syton) reduced this surface contribution to <10% of the total. The remaining surface absorption was not due to volatile impurities which could be removed by evacuation. The optimum resistivity range for germanium having the lowest bulk absorption coefficients at room temperature was found to be 10-40 ?-cm. It was also found that surface absorptions from germanium samples prepared by single-point diamond machining could be lower than those obtained after polishing with colloidal silica, although in many cases they were considerably higher.
