IDF Diabetes AtlasGlobal estimates of the prevalence of hyperglycaemia in pregnancy
Introduction
Until recently, any hyperglycaemia first detected during pregnancy was termed gestational diabetes [1]. However, this definition did not differentiate between different severity of hyperglycaemia. The World Health Organization recently proposed new criteria for the diagnosis and definition of hyperglycaemia first detected in pregnancy which distinguishes the more serious diabetes in pregnancy (DIP), which is more likely to persist beyond the birth, from gestational diabetes (GDM), a milder degree of hyperglycaemia [2]. The new definition calls for an understanding of the burden of hyperglycaemia in pregnancy and its relationship with the growing epidemic of type 2 diabetes and distinguishes DIP from GDM based on the degree of hyperglycaemia; a reflection that the risk of serious complications is much higher in diabetes than in the milder GDM. Where studies previously reported the prevalence of GDM, under the new definition, these figures would also include the more severe hyperglycaemia classified as diabetes in pregnancy (DIP) under the broad title of hyperglycaemia first-detected in pregnancy (HFDP). Adding to this definition pregnancy in women with known diabetes, we use the term hyperglycaemia in pregnancy (HIP) to describe the burden of any glucose intolerance in pregnancy. In previous studies, any level of glucose intolerance in pregnancy was termed GDM. A description of the terminology used in this paper and its relation to the estimates proposed is presented in Fig. 1.
HIP, including gestational diabetes mellitus (GDM) and total diabetes in pregnancy (TDP) (comprising both known diabetes in pregnant women, and previously undiagnosed diabetes in pregnancy (DIP)), is a common metabolic disorder during pregnancy and has been associated with serious perinatal complications for both mother and child. In the short-term, infants born to mothers with HFDP are at increased risk of foetal macrosomia (also known as large-for-gestational-age), hypoglycaemia and hyperinsulinemia at birth, and risks of shoulder dystocia associated with obstructed labour [3], [4]. Mothers with the condition are at increased risk of pre-eclampsia, gestational hypertension, caesarean section, and hydramnios [3], [4]. Moreover, TDP adds to these complications an increased risk of foetal malformations, foetal loss, perinatal and neonatal mortality, as well as an increased risk of maternal mortality [5], [6]. The growing numbers of younger adults with type 2 diabetes mellitus (T2DM) [7] may be contributing to rising trends in HIP.
Studies describing the risk factors and risk markers of gestational diabetes used the previous definition of the disease and there is some overlap with risk factors for T2DM. The presence of previously undiagnosed T2DM may play a role in the similarities. These risk factors and risk markers include: advancing age; obesity; excessive weight gain during pregnancy; a family history of diabetes; gestational diabetes during a previous pregnancy; a history of stillbirth or infant with congenital abnormality; and glycosuria during pregnancy [8], [9]. Similarly, certain ethnic groups found to have a higher prevalence of GDM have also been found to have a higher prevalence of T2DM [10], [11], [12]. GDM poses a long-term risk of developing T2DM for both mother [10] and possibly for the child as well [13] and may be contributing to the increasing global epidemic of T2DM. Despite this, a substantial proportion of women who develop GDM do not have a high-risk profile and some women who may be considered high-risk never develop the condition [14], [15].
Despite the serious public health implications of HIP, there has been is no universal definition and no universal standards for screening and a wide variety of methods are applied. Screening methods currently in use rely on variations of the oral glucose tolerance test whereby blood glucose is measured in the fasting state and again after an oral glucose challenge (Table 1). Depending on the criteria used the resulting prevalence can vary widely. A recent survey on GDM prevalence and practice administered among diabetologists and obstetricians in 173 countries found country-specific prevalence estimates ranging from < 1% in Germany up to 28% for a study in Nepal using a variety of criteria [16].
The lack of a uniform approach to estimate the prevalence of HIP, as well as the new definition from WHO, intensifies the need to develop a systematic means of estimating the prevalence of HIP using existing data. This paper presents the first estimates of the prevalence of HIP, including an estimated proportion of the figure which may be due to total (known and previously undiagnosed) diabetes in pregnancy (TDP), for the year 2013.
Section snippets
Methods
A detailed description of the methods used and the rationale for adjustments applied is available from Linnenkamp et al. [17]. Briefly, we conducted a systematic literature review of studies reporting the prevalence of gestational diabetes using the search terms: ‘gestational diabetes mellitus’, ‘GDM’, ‘prevalence’, ‘incidence’ and ‘screening’ and or. All studies reporting prevalence of GDM and conducted since 1980 were gathered and entered into a database for data cleaning, assessment, and
Statistical methods
Data management and analysis were done using the R statistical programme (version 2.15.2) [28] and a MySQL database to store study information and transformed estimates. Age-specific prevalence estimates of HFDP were calculated for women from 20 to 49 years in 5-year age-groups. Data from selected studies were smoothed using logistic regression models with a midpoint of each age-group as the independent variable and a weighted number of cases with and without HFDP as the dependent variable.
Estimates of hyperglycaemia in pregnancy and total diabetes in pregnancy
To align with the new WHO definition of HFDP which distinguishes DIP from GDM, we estimated the proportion of the HFDP prevalence that may be attributable to total diabetes in pregnancy (TDP) which would include DIP (previously undiagnosed diabetes in pregnancy) and estimates of the number of live births in women with known diabetes. The proportions were derived using age- and sex-specific prevalence of diabetes from the IDF Diabetes Atlas for women 20–49 for the year 2013 [7]. Using the same
Sensitivity analyses
Evidence from a single population-based study in women with type 1 diabetes in Sweden showed a standard fertility ratio (SFR) of 0.8 compared with women without diabetes [35]. We conducted a sensitivity analyses using this SFR and applying it to fertility rates when calculating the number of expected live births among women with diabetes to estimate the effect of reduced fertility in the population.
Results
We estimate that in 2013, 21.4 million out of an estimated 127.1 million live births to women aged 20–49 years (crude prevalence 16.9%; age-standardised prevalence 14.8%) were affected by hyperglycaemia in pregnancy of which 16% may be due to TDP including both previously undiagnosed diabetes in pregnancy, and live births in women with known diabetes. The South-East Asia Region had the highest crude prevalence of HIP at 23.1% of live births, followed closely by the Middle East and North Africa
Discussion
The estimates presented here indicate that with 21.4 million live births affected by hyperglycaemia in pregnancy in 2013, the condition poses a threat to global maternal health. The burden of HIP described in this paper, an estimated 170 cases per 1000 live births in 2013, puts it on par with other maternal conditions [37]. The prevalence of HIP increases sharply with age with a prevalence of 39.2% in women 40–44 and up to 47.9% in women 45–59 years, although fertility patterns have a profound
Limitations
The estimates presented in this paper must be interpreted with caution as they are based largely on extrapolation and a number of assumptions. The most substantial limitation to the estimates is the heterogeneity of methods used by the underlying studies to estimate the prevalence of HFDP. However, it is important to note that none of the screening criteria currently in use (Table 1) is lower than the values for diagnosis for the new WHO definition of HFDP (Fig. 1) and thus using these studies
Conclusion
Hyperglycaemia in pregnancy is a serious and growing global health threat to women. Integration of strategies for screening and managing women with the condition into public policy and health systems is essential. The growing numbers of women developing HIP will have implications not only for health systems, but will contribute to increases in the global diabetes epidemic.
Conflict of interest statement
The authors have no conflicts to disclose.
Acknowledgements
The authors wish to thank the IDF Diabetes Atlas Committee for reviewing and contributing to the methods used to generate these estimates. In addition, the authors wish to thank Prof. Boyd Metzger, Dr. David J. Pettitt, and Prof. Lois Jovanovič for independently reviewing the methodology. We also thank Dr. Lydia Makaroff for reading and commenting on the manuscript. The authors also wish to thank Dr. Gojka Roglic for her advice and contribution regarding the methodology and the estimates.
The
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