In a randomised controlled trial of vitamin D during pregnancy, we demonstrated that women with lower self-efficacy were more likely to experience practical problems with taking the trial medication and that this was associated with lower compliance and achieved 25(OH)-vitamin D concentrations.
The relationship between self-efficacy (the belief that one can carry out a behaviour), compliance with study protocol and outcome was explored within a randomised, double-blind, placebo-controlled trial of vitamin D supplementation in pregnancy.
In the Maternal Vitamin D Osteoporosis Study (MAVIDOS) trial, women with circulating plasma 25(OH)-vitamin D of 25–100 nmol/l in early pregnancy were randomised to either 1000 IU cholecalciferol/day or matched placebo from 14 weeks until delivery. Circulating 25(OH)-vitamin D concentrations were assessed at 14 and 34 weeks’ gestation. A sequential sub-sample completed Schwarzer’s General Self-Efficacy Scale at 14 and 34 weeks and the Problematic Experiences of Therapy Scale at 34 weeks. Women were interviewed about their experiences of the trial and interview transcripts analysed thematically.
In 203 women, those with higher self-efficacy were less likely to experience practical problems taking the study medication (odds ratio (OR) 0.81 (95 % confidence interval (CI) 0.69–0.95), p = 0.01). Over half reported practical problems associated with poorer compliance with the protocol requiring women to take the medication daily. Compliance in women who experienced practical problems was 94 % compared with 98 % for those with no problems (p < 0.001). Poorer compliance was also associated with lower concentrations of 25(OH)-D in late pregnancy in the treatment group (β = 0.54 nmol/l (95 % CI 0.18–0.89), p = 0.003). Thematic analysis suggested common difficulties were remembering to take the medication every day and swallowing the large capsules.
These findings suggest that differences in self-efficacy influence trial outcomes. Such information may help clinicians anticipate responses to routine vitamin D supplementation in pregnancy and identify those who may need more support to comply.
ISRCTN82927713, registered 11/04/2008.
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We thank all our funders for supporting this work (Arthritis Research UK, Medical Research Council, Bupa Foundation, National Institute for Health Research (NIHR) Southampton Biomedical Research Centre, University of Southampton and University Hospital Southampton NHS Foundation Trust, and NIHR Musculoskeletal Biomedical Research Unit, University of Oxford) and the women who so kindly gave us their time and took part in this study. MAVIDOS Trial Group: Nicholas J Bishop, Stephen Kennedy, Aris T Papageorghiou, Inez Schoenmakers, Robert Fraser, Saurabh V Gandhi, Andrew Carr, Sarah R Crozier, Rebecca J Moon, Nigel K Arden, Elaine M Dennison, Keith M Godfrey, Ann Prentice, M. Zulf Mughal, Richard Eastell, David M Reid, M Kassim Javaid.
Conflicts of interest
CC reports personal fees, consultancy, lecture fees and honoraria from Alliance for Better Bone Health, Amgen, Eli Lilly, GlaxoSmithKline, Medtronic, Merck, Novartis, Pfizer, Roche, Servier and Takeda, outside the submitted work. NCH reports personal fees, consultancy, lecture fees and honoraria from Alliance for Better Bone Health, AMGen, MSD, Eli Lilly, Servier, Shire, Consilient Healthcare and Internis Pharma, outside the submitted work. HMI reports grants from the Medical Research Council (MRC), Arthritis Research UK and European Union’s Seventh Framework Programme, during the conduct of the study; and while not directly receiving funding from other bodies, members of her team have received funding from the following companies for other work: Danone, Nestec and Abbott Nutrition. MB, JB and WL report funding from Danone Nutricia Early Life Nutrition for other work than that reported here. All other authors declare no competing interests.
This work was supported by grants from the Arthritis Research UK (17702), Medical Research Council (4050502589), Bupa Foundation, National Institute for Health Research (NIHR) Southampton Biomedical Research Centre, University of Southampton and University Hospital Southampton NHS Foundation Trust, and NIHR Musculoskeletal Biomedical Research Unit, University of Oxford. The work leading to these results was supported by the European Union’s Seventh Framework Programme (FP7/2007-2013), projects EarlyNutrition and ODIN under grant agreements numbers 289346 and 613977. We are extremely grateful to Merck GmbH for the kind provision of the Vigantoletten supplement. Merck GmbH had no role in the trial execution, data collection, analysis or manuscript preparation. The authors had full access to all study data.
Cyrus Cooper and Nicholas C. Harvey are joint senior authors.
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Barker, M., D’Angelo, S., Ntani, G. et al. The relationship between maternal self-efficacy, compliance and outcome in a trial of vitamin D supplementation in pregnancy. Osteoporos Int 28, 77–84 (2017). https://doi.org/10.1007/s00198-016-3721-5
- Randomised controlled trial
- Vitamin D