Características de las conductas y estímulos implicados en la experiencia del individuo

The two electronic databases, MEDLINE and EMBASE were used to search the literature on prevalence of GDM from January 1996 through July 2013. All reference lists from the main reports and relevant reviews were hand-searched. In addition, the following subject headings and text words, and their combinations were included in electronic database search strategy (incidence or epidemiolog* and prevalence and gestation* diabet* or GDM or pregnan* and diabet* and burden), as detailed in Appendix 1.

All retrieved studies were initially screened by title and abstract, then the exclusion/ inclusion criteria were applied. If it was concluded that an article should be included for systematic review, the full text of the article was obtained. Based on the full text manuscripts, studies were selected according to whether they matched predefined criteria.

5.2.2 Eligibility criteria

The newly published, Preferred Reporting Items for Systematic reviews and Meta-Analysed (PRISMA), provides guidelines for conducting systematic reviews, and suggests framing questions with five components to help facilitate the systematic review and meta-analysis process. Inclusion criteria are presented as five PICOS components namely, the patient population or the disease being addressed (P), the intervention or exposure (I), the comparator group (C), the outcome or endpoint (O), and the study design chosen (S) (Liberati et al., 2009). Predefined criteria were applied to choose the final list of papers to be included in the review based on the inclusion criteria presented as five PICOS components, as shown in Table 5.1.

Table 5.1 Eligibility criteria in PICOS components PICOS components Inclusion criteria

Populations(P) Participants of any age of pregnancy. GDM was described as carbohydrate intolerance of varying degrees of severity, with onset or first recognition during pregnancy.

Intervention(I) All screening test techniques and procedure

Comparative (C) -

Outcome (O) Papers which attempted to identity the prevalence of GDM as their primary objective were included, a subject has been identified for GDM papers provided a prevalent number (usually shown as a percentage) and 95%

confident interval for the whole population or sub-populations of gestational diabetes mellitus were included

Study design chosen (S) Cross-sectional study design or cohort studies.

Exclusion criteria included papers not in the English language, case studies based on a single case and prevalence numbers where patients were already known to have diabetes mellitus before pregnancy. Studies that report only prevalence trends for GDM over a number of years were also omitted. Additionally, papers consisting of abstracts only were omitted. However the potential for selection bias is recognised particularly with regard to English language and abstract exclusion.

5.2.3 Data collection process

All information about the methodology and results from each study were extracted using a data extraction collection form. Abstracted information included study characteristics and study results as well as other items; the study’s location and population, PICOS, study’s design, screening test criteria and threshold, and prevalence.

5.2.4 Methodological quality assessment

No generally accepted criteria for the quality assessment of prevalence studies were available. This systematic review applied and adopted the quality assessment list of previous systematic reviews of prevalence (Bishop et al., 2010) (Prins et al., 2002).

Regarding the methodological quality of those studies, two aspects of validity are important: external validity and internal validity. External validity relates to the applicability of study results to other populations, whereas internal validity implies accurate measurement apart from random error. This quality assessment covers all aspects of the prevalence article including items deemed essential for the transparent reporting of a systematic review of prevalence studies. A checklist was designed that consists of 15 items: six items on internal validity; six items on external validity and; three items on informativity, as shown in Appendix 3. The quality assessments were scored for each item as positive (Yes) or Negative (No) and were not weighted for importance. If an item was

yes, its score equals one, whereas if an item was no, its score equals zero. The scores of the 15 items were summed up and presented as a total score for each study.

5.2.5 Statistical analysis methods

Descriptive statistics were used to summarise the quality of papers and the characteristics of the studies in accordance with the guidelines in the PRISMA statement (Liberati et al., 2009). The prevalence and its confidence interval (CI) were plotted for each study in a forest plot-type chart. Prevalence’s were then grouped according to the characteristics of the respective screening tests and population, as detailed in Table 5.2; screening test procedures, risk factor (ethnic group) and screening test guidelines.

The screening procedures groups were broken down into two groups, universal and selective screening. Selective screening initially screens all pregnant women with risk factors. The studies were then grouped according to the main risk factors detailed in the work by National Institute for Clinical Excellence (NICE) and The Fourth International Workshop-Conference on Gestational Diabetes Mellitus (National Health Service, 2008b) (Metzger and Coustan, 1998). The risk factors are obesity, age greater than 25 years, family history of diabetes, history of previous GDM and ethnic group. Ethnic background was divided into two groups related to a high and low risk for GDM, based on the guidelines. The difference in screening test guidelines used may play a major part in the different incidences of GDM as well as screening procedures. However, if appropriate results were obtained from individual studies it was planned to estimate the overall prevalence of GDM using analysis. Many systematic reviews contain meta-analyses, but not all.

Table 5.2 The characteristics of screening tests for GDM Characteristics Details

Screening procedure Universal screening: screen all pregnant women by measurement of plasma glucose between 24 and 28 weeks using different test techniques

Selective screening: screen initially all pregnant women with risk factors. In the next stage, women who show positive risk factors undergo further screening

Ethnicity group High risk groups of GDM: South Asian, Back Caribbean, Middle Eastern, South-East Asian, Aborigine, Hispanic, African and Pacific Islands.

Low risk groups of GDM: Other nationalities Screening test guideline Based on the guidelines used in the study