Notes: To compare newborn outcomes and costs of hospital stays for twins born to mothers receiving care in a specialized twin clinic with a research-based care protocol and one consistent caregiver versus twins ?whose mothers received standard prenatal care.Design and Setting: A retrospective, historical cohort study conducted in a high-risk obstetric clinic in central Texas.〈section xml:id="abs1-2"〉〈title type="main"〉Patients: Thirty women pregnant with twins received Specialized care. The comparison group consisted of 41 women pregnant with twins who received standard care.〈section xml:id="abs1-3"〉〈title type="main"〉Interventions: An advanced practice nurse provided prenatal care, which included weekly clinic visits, home visits, and 24-hour availability for phone support.〈section xml:id="abs1-4"〉〈title type="main"〉Outcome Measures: Gestational age at birth, birth weight, length of stay in the neonatal intensive-care unit (NICU), and hospital charges for the new-borns.〈section xml:id="abs1-5"〉〈title type="main"〉Results: No newborns of less than 30 weeks gestation were born to women in the specialized care group, the mean birth weight was 249 g (SD ± 77) higher, days in the NICU were reduced from a mean of 17 to 7, and hospital charges were $30,000 less per infant.〈section xml:id="abs1-6"〉〈title type="main"〉Conclusions: Newborn outcomes were improved and length of stlay and hospital charges were significantly reduced for newborns whose mothers had received care in the specialized twin clinic.

Notes: Abstract Previous stable isotope studies at Lizzies Basin revealed that metasedimentary rocks are 18O-depleted relative to protolith values, particularly in the lower parts of the section (Lower Zone) where the rocks are also isotopically homogeneous on a scale of hundreds of meters (quartz δ18O=+9.0 to +9.6 per mil). In contrast, metasedimentary rocks at higher levels at Lizzies Basin (Upper Zone) are less 18O-depleted and more heterogeneous in δ18O. In order to understand more fully the isotopic evolution of this terrane, a series of detailed, meter-scale traverses across various metamorphic and igneous lithologies were completed at Lizzies Basin, and at the structurally higher Angel Lake locality. Traverses in the Lizzies Basin Lower Zone and in the lower parts of Angel Lake (Angel Lake Lower Sequence) across various silicate lithologies, including abundant granitoids, reveal similar degrees of homogeneity, although the average δ18O values are higher at Angel Lake. In contrast, traverses which include substantial thicknesses of marble and calc-silicate gneiss and very little granitoid have more heterogeneous quartz δ18O values (+11.9 to +13.4 per mil), and also have a higher average δ18O (+12.9 per mil), than observed elsewhere. The scale of 18O/16O homogeneity in quartz observed at Lizzies Basin and Angel Lake (meters to hundreds of meters) requires fluid-mediated isotope exchange, which accompanied Tertiary metamorphism. There is a correlation between the degree of 18O-depletion in metasedimentary rocks, 18O/16O homogenization between lithologies, and the proportion of granitoids (leucogranites in particular) within any part of the section, and a corresponding anticor-relation with the proportion of marble. This points to a causal relationship, whereby the leucogranites (as well as the Tertiary hornblende diorite and biotite monzogranite) acted as both a relatively low-18O reservoir and a source of fluids to enhance exchange, while the marbles hindered isotope deplction and homogenization by acting as relatively high-18O reservoirs and impermeable layers. Material balance calculations help delineate the plausible mechanisms of exchange between granitoids and metasediments. Single-pass infiltration of magmatic fluids from the granitoids is not capable of reproducing all of the observations. Fluidmediated exchange by convective recirculation of magmatic fluids on a scale of meters is the mechanism which explains all of the observations. The generalized model for the isotopic evolution of the East Humboldt Range core complex provides and excellent opportunity to establish the main causes and controlling factors of 18O-depletion and 18O/16O homogenization during regional metamorphism.

Notes: Abstract 18O/16O ratios vary systematically in the 1,000 m section of interlayered metasediments and granitoids at Lizzies Basin, the deepest structural level exposed in the East Humboldt Range metamorphic core complex. In the lower 300 m of the section (the Lower Zone) δ18O is homogeneous and low (+6.6 to +8.8 in silicate rocks, +8.7 to +12.1 in marbles). A detailed oxygen isotope profile across an individual marble layer within the Lower Zone has a similar range in δ18O (+9.5 to +11.9) with the highest values preserved in the middle of the layer. In the upper 700 m of the section (the Upper Zone) metasediments have been less strongly 18O depleted. The δ18O values are higher and more heterogeneous and in a profile across a marble layer of similar thickness, rise steeply from marginal values of +12 to core values of +23. Quartz from silicate metasediments throughout the Upper Zone ranges from +11 to +13 and is thus fairly homogeneous, particularly where detailed profiles have been measured adjacent to the 18O-rich marble layers. Covariation of 18O/16O and 13C/12C ratios in marbles suggests that the isotopic composition of these elements has been altered by exchange with infiltrating, water-rich, CO2−H2O fluids with mantle-like isotopic composition. In most cases, marble cores preserve protolith δ13C values and these vary systematically throughout the section according to structural level, including some exceptionally 13C-rich values up to +12. This range may reflect stratigraphic variation in δ13C of the Proterozoic sedimentary protoliths of these rocks. The Upper/Lower Zone boundary, and the contrast in isotope systematics to either side, has been previously explained either as an impermeable barrier to fluid flow, or as an infiltration front (Wickham and Peters 1990). The second alternative has been tested using a numerical model in which low-18O aqueous fluid flows vertically upward through an alternating sequence of monomineralic quartz (δ18O=+12) and calcite (δ18O=+22) layers in a regime in which the oxygen isotopic composition is controlled by advection, diffusion (in the fluid), and fluid/solid exchange. Solutions to the relevant transport equations indicate that the abrupt change in the average δ18O value of the layers at the Upper/Lower Zone boundary can be reproduced by the model with a uniform porosity throughout the system, but the observed contrast in the shapes of the marble layer profiles in the Upper and Lower Zones cannot be reproduced under these conditions. However, if the calcite layers have two orders of magnitude lower porosity in comparison with the quartz layers and exchange within them is diffusion-dominated (as opposed to advection-dominated in the quartz) the contrasting shapes of the marble profiles in the two zones are reproduced, as well as the Upper/Lower Zone discontinuity. The range of conditions that generates both an infiltration front (at the appropriate scale) and contrasting marble profiles (at the appropriate scale) is quite narrow but requires a volatile flux that could be generated by plausible volumes of mantle-derived magma crystallizing at depth beneath the area, providing support for this mechanism as a viable agent of 18O depletion in the deep-level rocks of this terrane.