Biomedical subjects

H McCallum

Publications and source records attributed to H McCallum.

10 recordsLinked to original sources

PubMed2006

Effect of B vitamins and genetics on success of in-vitro fertilisation: prospective cohort study.

BACKGROUND: There is a need to understand what affects the success of in-vitro fertilisation (IVF) and the rate of resulting twin births so that pregnancy rates can be improved and multiple gestations avoided. Our aim was to assess the role of B vitamins and genetics. METHODS: We did a prospective cohort study of 602 women undergoing fertility treatment. We assessed intake of folate and vitamin B12 with a questionnaire and measured their plasma and red-blood-cell concentrations by radioimmunoassay. We measured five B-vitamin-related gene variants in women who received treatment and in 932 women who conceived naturally. FINDINGS: The likelihood of a twin birth after IVF rose with increased concentrations of plasma folate (1.52, 1.01-2.28; p=0.032) and red-cell folate (1.28, 1.00-1.65; p=0.039). There was no association between folate and vitamin B12 levels and likelihood of a successful pregnancy. Women homozygous for the 1298 CC variant of methylenetetrahydro-folate reductase (MTHFR), rather than the AA variant, were less likely to produce a livebirth after IVF (0.24, 0.08-0.71; p=0.003) or to have had a previous pregnancy (0.42, 0.21-0.81; p=0.008). INTERPRETATION: Our findings suggest that MTHFR genotype is linked to a woman's potential to produce healthy embryos (possibly through interaction with genes related to DNA methylation). In women likely to have a successful IVF pregnancy, high folate status increases the likelihood of twin birth after multiple embryo transfer. Proposals to fortify the UK diet with folic acid could lead to an increase in the number of twins born after IVF.

Chorionic Gonadotropin↗

PubMed2001

How should pathogen transmission be modelled?

Host-pathogen models are essential for designing strategies for managing disease threats to humans, wild animals and domestic animals. The behaviour of these models is greatly affected by the way in which transmission between infected and susceptible hosts is modelled. Since host-pathogen models were first developed at the beginning of the 20th century, the 'mass action' assumption has almost always been used for transmission. Recently, however, it has been suggested that mass action has often been modelled wrongly. Alternative models of transmission are beginning to appear, as are empirical tests of transmission dynamics.

Journal Article↗

PubMed2001

Paediatric pelvic imaging: improvement in gonad shield placement by multidisciplinary audit.

BACKGROUND: In 1996, there were local reports of poor gonad protection for paediatric pelvic radiographs. OBJECTIVES: To investigate the nature of the problem and make necessary improvements. MATERIALS AND METHODS: A retrospective audit of 218 paediatric pelvic radiographs was undertaken in 1997. Each radiograph was assessed for the presence of a gonad shield, appropriateness of the device and its position. A multidisciplinary team was formed with representation from radiology, radiography, orthopaedics and medical physics to investigate ways of improving technique and reducing patient dose. These included radiographer training and the introduction of digital fluoroscopy as an alternative imaging technique in follow-up patients. There were further rounds of data collection in 1998 and 1999. RESULTS: In round 1, a gonad shield was present in 77.9 % of boys' films and 76 % of girls' films where one should have been, increasing to 85.2 % and 85.4 % respectively by round 3 of the audit (P < 0.05). Only 31.6 % of boys' devices and 21.9 % of girls' devices were correctly positioned in round 1, increasing to 78.3 % and 94.3 %, respectively, by round 3 of the audit (P < 0.05). After round 1, no inappropriate devices were used. CONCLUSION: Audit was an effective tool in gaining the resources needed to improve technique and reduce radiation exposure in children. The multidisciplinary approach was vital in the success of this project.

Child, Preschool↗

PubMed1997

The impact of cardiology on the collective effective dose in the North of England.

Two cardiology X-ray rooms were monitored with dose-area product meters as part of a Regional Patient Dosimetry Programme. Dose-area product measurements on over 2000 patients undergoing examinations in the cardiology rooms are presented. The data have been corrected according to patient size where possible. In room A mean dose-area product values for coronary angiography, coronary angioplasty, radiofrequency ablation and mitral valvuloplasty were found to be 47.7, 72.2, 91.1 and 161.9 Gy cm2 respectively. In room B mean dose-area product values for coronary angiography and coronary angioplasty were found to be 23.4 and 51.6 Gy cm2 respectively. Observational studies were used to deduce the typical projections and technique factors. This typical examination was used to simulate an angiogram from which it was possible to derive factors to convert measured dose-area product values into estimates of effective dose. In room A, the effective doses were estimated to be 9.4, 14.2, 17.3 and 29.3 mSv for coronary angiography, coronary angioplasty, radiofrequency ablation and mitral valvuloplasty, respectively. The effective doses during coronary angiography and coronary angioplasty, performed in room B, were found to be 4.6 and 10.2 mSv, respectively. A regional survey of the frequency of these cardiac procedures was performed. It was deduced that the annual collective effective dose from these cardiac procedures in the North of England, the former Northern Region, was 45.7 manSv.

Angioplasty↗

PubMed1975