The effectiveness of risk score-based selective screening under IADPSG

A risk score-based selective screening approach for GDM was developed and assessed under new IADPSG criteria in China. A risk scoring algorithm for identifying high risk pregnant women was established, using existing and novel risk factors identified from the nested case-control study. By using a cut-off score of 0.37, the risk score-based selective screening approach yielded a sensitivity of 80% and a specificity of 45%. . Using this approach, on one hand, 45% of the non-GDM, which is 41% of the whole pregnant population were correctly identified as low-risk women and thereby spared from the unnecessary OGTT screening test. While this indicates potential for significant monetary savings for the country and prevention of unnecessary burden for pregnant women, this approach carries possible risks. The advantages were available at the cost of missing 20% of the GDM women, which percentage represented 2% of the pregnant population, thereby highlighting concerns when making a decision as to the adoption of the optimal screening approach.

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6.2.1 Universal versus selective screening for GDM

Two systematic reviews (Hieronimus & Le Meaux, 2010; Tieu et al., 2010) and two health technology assessment (HTA) reports (Scott et al., 2002; Waugh et al., 2010) have been conducted previously, involving a comparison of universal versus selective screening. They were limited due to either the databases searched (Hieronimus & Le Meaux, 2010), the types of study included (Tieu et al., 2010), or the focus and number of the effectiveness studies included (Scott et al., 2002; Waugh et al., 2010).

Hieronimus and Le Meaux (2010) used efficacy outcome measures of sensitivity and specificity for effectiveness studies. However, they searched only two databases of Medline and Cochrane database from 1990 to 2010, and did not assess the quality of the included studies. A total of 14 effectiveness studies were included in the review, which concluded that the benefit of GDM screening and treatment were only proven in women presenting GDM risk factors, while the relevance of screening for women with no risk factors remained controversial. Tieu et al. (2010) evaluated the screening, diagnosis and treatment of GDM, and included only randomised and quasi-randomised trials. Only one quasi-experimental study (Griffin et al., 2000) was identified comparing the clinical outcome measures of the two screening approaches, which in itself reflects bias and limitations. Tieu et al. (2010) did not make a definite conclusion about which screening approach should be recommended. Scott et al., (2002) and Waugh et al. (2010) evaluated the treatment and screening for GDM. Each of these reviews involved a short sub-section discussing risk factor screening compared to universal screening. Only nine effectiveness studies were described in the review by Scott et al., indicating that selective screening on the basis of risk factors would miss about half of the women with GDM. Waugh et al. (2010)

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included an additional study by Cosson et al. (2006) with regards to the effectiveness of selective screening versus universal screening to the review by Scott et al.

The current systematic review extended and updated the previous reviews by using broader types of study designs, including the recent studies published after 2010 as well as fully analysing the efficacy outcome measures of sensitivity and specificity of selective screening in comparison with universal screening. This is the most comprehensive and up-to-date systematic review on universal versus selective screening up till this point, and a number of informative conclusions as to the two approaches have been drawn in comparison with those of the four preceding reviews.

6.2.2 Pregnant women’s perspectives of GDM screening

In line with the participant views expressed in the single study done by Griffiths et al. (1993) in Australia which explored the attitudes of pregnant women toward universal one-step GDM screening with modified OGTT, the participants of this current study also generally felt it was important and necessary to conduct a screening test for all pregnant women. However, unlike positive attitudes towards the convenience of the screening method used in Australia, non-GDM pregnant women in China tended to feel that the OGTT test was not convenient at all, and that it was potentially burdensome. This may be attributable to the difference in the GDM screening tests administered in the Australian study and those administered in the current study in China. In the Australian study, a 75g OGTT involved one blood sample taken in a fasting state either at home or in a collection center, followed by a further blood sample taken after 2 hours. Whereas in China, a 75g OGTT involved one blood sample taken in a fasting state at the hospital, followed by two blood samples taken after 1 hour and 2 hours. The 75g OGTT was more complicated in the current study in China. Apart from the differences in OGTT itself, there might be

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other contributors to their attitudes including cultural issues and knowledge about OGTT before undergoing the test. The Q methodology study showed that 63.6% of factor 2 participants and 92.3% of factor 1 participants received GDM information before undergoing OGTT. Health education about GDM and OGTT before the test would make the OGTT process more acceptable.

6.2.3 The effectiveness of risk score-based selective screening under IADPSG

Four previous studies developed and used their own developed selection criteria for identifying high risk women for GDM screening (Caliskan et al., 2014; Naylor et al., 1997; Van Leeuwen et al., 2010; Pintaudi et al., 2014). Two of these used a risk scoring algorithm and were conducted in Canada (Naylor et al., 1997) and the Netherlands (Van Leeuwen et al., 2010) respectively. Naylor et al. (1997) found that risk score-based selective screening achieved a sensitive of 90.6% and specificity of 34.7%, while Van Leeuwen et al. (2010)’s risk scoring algorithm reached a sensitivity of 75.0% and a specificity of 57.0%. Both studies recommended selective screening over universal screening as a conclusion.

The findings of the current risk scoring study in China were consistent with and supported the two previous risk scoring studies. It found that the risk scoring algorithm yielded a sensitive of 80% and a specificity of 45%. It may be noticed that there were differences in setting among the three studies. The Canadian study used two-step GDM tests and had a GDM prevalence of 2.1% in 1997 (Naylor et al., 1997). The Netherlands study used two-step GDM tests and had a GDM prevalence of 4.6% in 2010 (Van Leeuwen et al., 2010). For the current study in China, the one- step GDM test using IADPSG criteria was used and the incidence of GDM was 9.4%.

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Despite the differences in settings, selective screening using a risk scoring algorithm nonetheless seemed to be effective.

6.3 STUDY STRENGTHS AND LIMITATIONS