Hyperpolarized129 Xe NMR can detect the presence of specific lowconcentration biomolecular analytes by means of the xenon biosensor, which consists of a water-soluble, targeted cryptophane-A cage that encapsulates xenon. In this work we use the prototypical biotinylated xenon biosensor to determine the relationship between the molecular composition of the xenon biosensor and the characteristics of protein-bound resonances.The effects of diastereomer overlap, dipole-dipole coupling, chemical shift anisotropy, xenon exchange, and biosensor conformational exchange on protein-bound biosensor signal were assessed. It was found that optimal protein-bound biosensor signal can be obtained by minimizing the number of biosensor diastereomers and using a flexible linker of appropriate length.Both the linewidth and sensitivity of chemical shift to protein binding of the xenon biosensor were found to be inversely proportional to linker length.

Objective To estimate how well a convenience sample of women from the general population could self-screen for contraindications to combined oral contraceptives using a medical checklist. Methods Women 18-49 years old (N=1,271) were recruited at two shopping malls and a flea market in El Paso, Texas, and asked first whether they thought pills were medically safe for them. They then used a checklist to determine the presence of level 3 or 4 contraindications to combined oral contraceptives according to the World Health Organization Medical Eligibility Criteria. Women were then interviewed by a blinded nurse practitioner who also measured blood pressure. Results The sensitivity of the unaided self-screen to detect true contraindications was 56.2% (95% CI: 51.7%-60.6%) and specificity 57.6% (54.0%-61.1%). The sensitivity of the checklist to detect true contraindications was 83.2% (79.5%-86.3%) and specificity 88.8% (86.3%- 90.9%). Using the checklist, 6.6% (5.2%-8.0%) of women incorrectly thought they were eligible for use when, in fact, they were contraindicated, largely due to unrecognized hypertension. Seven percent (5.4%-8.2%) of women incorrectly thought they were contraindicated when they truly were not, primarily due to misclassification of migraine headaches. In regression analysis, younger women, more educated women and Spanish-speakers were significantly more likely to correctly self-screen (p<0.05). Conclusion Self-screening for contraindications to oral contraceptives using a medical checklist is relatively accurate. Unaided screening is inaccurate and reflects common misperceptions about the safety of oral contraceptives. Over-the-counter provision of this method would likely be safe, especially for younger women and if independent blood pressure screening were encouraged.

Maternal mortality among indigenous women in Guatemala is high. To reduce deaths during transport from far-away rural communities to the hospital, maternity waiting homes (MWH) were established near to hospitals where women with high-risk pregnancies await their delivery before being transferred for labour to the hospital. However, the homes are under-utilised. We conducted a qualitative study with 48 stakeholders (MWH users, family members, community leaders, MWH staff, Mayan midwives and health centre and hospital medical staff) in Huehuetenango and Cuilco to identify barriers before, during and after the women's stay in the homes. The women most in need - indigenous women from remote areas - seemed to have least access to the MWHs. Service users' lack of knowledge about the existence of the homes, limited provision of culturally appropriate care and a lack of sustainable funding were the most important problems identified. While the strategy of MWHs has the potential to contribute to the prevention of maternal (as well as newborn) deaths in rural Guatemala, they can only function effectively if they are planned and implemented with community involvement and support, through a participatory approach.