Gestational diabetes in Saudi women identified by the International Association of Diabetes and Pregnancy Study Group versus the former American Diabetes Association criteria: a prospective cohort study

Introduction

In March 2010, the International Association of Diabetes and Pregnancy Study Groups (IADPSG) proposed new criteria for the diagnosis of gestational diabetes mellitus (GDM), aiming to standardize the criteria worldwide.¹ These recommendations are based on the results of the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study, which showed a continuous linear association between maternal glycemia and adverse fetal outcomes.² The prevalence of GDM increased after adoption of the IADPSG criteria. ^3–12 This increase in prevalence was mainly due to a single abnormal value in the oral glucose tolerance test (OGTT) that is required to diagnose GDM. The cutoff values for fasting, 1- and 2-h glucose are slightly lower than in most of the other criteria. For this reason, there is still controversy on the adoption of IADPSG worldwide. In January 2011, the American Diabetes Association (ADA) endorsed the IADPSG recommendations. ¹³ Recently, the Endocrine Society and the WHO endorsed the IADPSG recommendations.^{14, 15} However, the American College of Obstetricians and Gynecologists¹⁶ and the National Institutes of Health¹⁷ have not endorsed the IADPSG recommendations and still recommend the traditional “two-step approach” of screening with a 1-h 50-g glucose load test followed by a 3-h 100-g OGTT for those with a positive screening. In the 2014 Standards of Care, ADA readdressed the NIH consensus along with the IADPSG guidelines because there were insufficient data to strongly demonstrate the superiority of one strategy over the other.¹⁸

The prevalence of GDM in Saudi women was previously reported as 12.5%.^19,20 Recently, Al-Rubeaan et al²¹ reported a higher prevalence of GDM among Saudi women (36.6%) by applying partial IADPSG criteria for screening for GDM with fasting glucose levels only, without performing OGTT.²¹

There are contradictions between the studies on the impact of the IADPSG recommendations on pregnancy outcome.^10,11,22 In some studies, GDM identified by IADPSG criteria have the same adverse pregnancy outcomes as GDM identified by the older criteria both of which differ from non-GDM cases.^10,22 However, another study did not find differences.¹¹ We performed this study to compare the IADPSG criteria with the former ADA criteria before adopting the IADPSG recommendations. We intended to compare the frequency, clinical characteristics and pregnancy outcomes identified by each criterion among Saudi women.

PATIENTS AND METHODS

Consecutive pregnant women treated in the antenatal service at the Maternity and Children Hospital in Medina, Saudi Arabia, from October 2011 to August 2012 were recruited for this prospective cohort study. Women were eligible if they were of Saudi nationality, with a singleton pregnancy, planned to give birth at the study hospital, and were able to give written consent to participate. The exclusion criteria included pre-existing diabetes, non-Saudi nationality, unwillingness to deliver at the study hospital, multiple pregnancies, and chronic diseases and drugs that might affect pregnancy outcomes. The study was approved by the ethical committees of King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia, and the Maternity and Children Hospital, Medina, Saudi Arabia. All of the participants provided written informed consent.

Demographic data were obtained from all participants at the first antenatal visit. Each participant was assessed for risk factors for GDM including age, parity, family history of diabetes, and history of GDM, macrosomic infant (birth weight ≥4000 g), stillbirth, and unexplained neonatal death. Anthropometric measurements, including weight, height and body mass index (BMI) and blood pressure were taken and urine analysis was performed on all participants.

All participants performed a 75-g OGTT for 2 hours between 24–28 weeks of gestation. Gestational diabetes was diagnosed according to the IADPSG and the former ADA criteria, respectively. The cut-off values in the IADPSG criteria include fasting plasma glucose (FPG) ≥92 mg/dL (5.1 mmol/L), 1-h postprandial glucose (PPG) ≥180 mg/dL (10 mmol/L) or 2-h PPG ≥153 mg/dL (8.5 mmol/L) with a single abnormal value needed for GDM diagnosis. The cut-off values in the former ADA criteria included: FPG ≥95 mg/dL (5.3 mmol/L), 1-h PPG ≥180 mg/dL (10 mmol/L) or 2-h PPG ≥155 mg/dL (8.6 mmol/L) with at least two abnormal values needed for diagnosis.²³ All women diagnosed with GDM by any criteria were treated by diet and exercise. Insulin was added if the glycemic targets were not achieved. The glycemic targets were as follow: FG ≤90 mg/dL (5.0 mmol/L), 1-h post-meal: ≤140 mg/dL (7.8 mmol/L) or 2-h post-meal: ≤120 mg/dL (6.7 mmol/L).²³ All of the women were followed up until delivery by obstetricians. Additionally, a specialist team, consisting of an internal medicine physician, a diabetic educator, and a dietician, followed up the GDM patients.

After delivery, the medical records of all of the mothers and neonates were checked for pregnancy and neonatal outcomes. The fetal variables collected were weight, Apgar score at 5 min (>7 considered acceptable), congenital malformations, shoulder dystocia, fetal distress, hypoglycemia, hyperbilirubinemia, stillbirths, and admission to the neonatal intensive care unit and neonatal death. Macrosomia was defined as a birth weight of 4000 g or more. Neonatal hypoglycemia was defined as blood glucose levels below 2.2 mmol/L (40 mg/dL). For the detection of hypoglycemia, blood glucose monitoring was done to the newborns of GDM mothers and to those with macrosomia at half an hour after delivery, every 2 hours for 2 readings and then every 3 hours before the following 3 feedings.

Maternal outcomes were noted for polyhydramnios (diagnosed clinically or by ultrasound if the amniotic fluid index exceeded 24 cm or a single deepest pocket of fluid of at least 8 cm), preterm delivery (defined as <37 weeks of gestation), premature rupture of membranes (PROM), type of delivery, induction of labor, lacerations, admission to the intensive care unit, and days of hospitalization.

The women were divided into three groups: GDM diagnosed by both criteria (group 1), additional GDM identified by the IADPSG criteria only (group 2), and normal by both criteria (group 3). Comparisons between the three groups were made in terms of clinical and metabolic characteristics and pregnancy outcomes. Measurements of serum glucose were performed by the glucose oxidase method. Measurements of HbA1C were performed at the time of entry into the study, by standardized HPLC. We included all women who attended the clinical and had an OGTT during the period between October 2011 and August 2012.

Statistical analyses were performed using SPSS software (v 16.0; SPSS Inc, Chicago, IL). Data are expressed as mean (standard deviation, SD), median (minimum and maximum), or percentages. Groups were compared using ANOVA followed by a post-hoc analysis (for continuous data), and the χ²-test (for frequency data), otherwise the Mann-Whitney U test was used for comparison of medians. A divided χ² analysis was used when the null hypothesis was rejected to explore which category contributed to the difference. Whether the distributions of continuous variables were normal or not was determined by the Shapiro–Wilk test. A P value of <.05 (two-tailed) was considered significant.

RESULTS

The mean (SD) age of the 277 women included in the study was 30.8 (6.2) years, weight 70.3 (1.5) kg, and BMI 29.5 (6.3). Multiparity, previous GDM and family history of DM were present in 56.5%, 13.8% and 59.1%, respectively (Table 1). The number of women diagnosed with GDM using the former ADA criteria was 47 (16.9%) and by the IADPSG criteria 115 (41.5%). The IADPSG criteria identified all women with GDM by the former ADA criteria and categorized an additional 68 cases of GDM. Thus, there were 47 women in the group identified by both criteria; 68 women in the group identified only by the IADPSG criteria; and 162 women in the normal glucose tolerance (NGT) group (NGT by both criteria). Most (89.7%) of the additional cases of GDM identified by the IADPSG criteria as a result of a single abnormal glucose value during the OGTT.

The additional GDM group identified by the IADPSG criteria had the same clinical and metabolic characteristics as the GDM group identified by both criteria except for lower systolic blood pressure (P=.001), lower diastolic blood pressure (P=.02), and less frequent glycosuria (P=.01). The clinical and metabolic characteristics of the additional GDM group identified by the IADPSG criteria differed from the NGT group in age, weight, previous diagnosis of GDM, history of recurrent abortions, and glucose levels during OGTT and HbA1c (Table 1).

DISCUSSION

This is the first study that has prospectively compared clinical characteristics and pregnancy outcomes of treated GDM cases as identified by the IADPSG criteria versus those identified by the former ADA criteria. Studies from Italy,¹⁰ Canada,¹¹ and Belgium,²² compared clinical characteristics and pregnancy outcomes in additional cases of GDM identified by the IADPSG criteria that were considered normal by the former criteria. However, all of these studies were retrospective and therefore the reclassified GDM group had not been treated. In addition, the Italian and the Belgian studies used 100-g OGTT instead of the 75 g as recommended by the IADPSG, and therefore the new GDM group in the latter two studies might include women without GDM by the IADPSG criteria if a 75-g OGTT had been used.

In the current study, the frequency of GDM among Saudi women was 41.5% by the IADPSG criteria and 16.9% by the former ADA criteria, indicating a 2.44- fold (144.6%) increase in the GDM frequency when applying the IADPSG criteria. This is consistent with the findings from recent studies, which showed significant increases in the GDM prevalence worldwide, by 1.24 to three-fold (P=.001), when applying the IADPSG criteria^3–10,12 (Table 3). The combined prevalence of GDM in the HAPO study based on the IADPSG criteria was 17.8%, but it varied substantially among different centers, with the lowest prevalence in Israel (9.3%), and the highest prevalence in the US (Bellflower, CA) (25.5%). This increment in the GDM prevalence increases the load on the health care system and may increase the likelihood of interventions. On the other hand, there are expected benefits to these pregnancies and the increase in cases identified might provide an opportunity to help more pregnant women avoid diabetes in the future. The additional cases of GDM identified by the IADPSG criteria mainly resulted from a single abnormal glucose value during OGTT (in 89.7% of patients), which was the case in the Italian¹⁰ and Belgian²² studies.

In the current study, the additional IADPSG-GDM group did have the same clinical characteristics and GDM risks as the GDM identified by both criteria, except for having lower blood pressure and less frequent glycosuria. On the contrary, in the Belgian²² and the Italian studies,¹⁰ the additional IADPSG-GDM groups were significantly younger compared with the GDM group diagnosed by the Carpenter and Coustan criteria. In addition, in the latter study, the pre-pregnancy BMI in this group was lower compared with the GDM group diagnosed by the older criteria.

In our study, the individuals in the additional IADPSG-GDM group were older and heavier and had a higher frequency of previous GDM and recurrent abortions than women with NGT. In a Canadian study, the authors reported higher rates of advanced maternal age, obesity, and previous GDM in women classified as GDM by the IADPSG criteria who did not fulfill the Canadian Diabetes Association criteria (CDA) for GDM or gestational glucose intolerance.¹¹ This finding is consistent with our results.

The additional IADPSG-GDM group in our study had the same pregnancy outcomes as women considered to have GDM by both criteria, and they differed significantly, in some outcomes, from the NGT group. This is in agreement with the Italian¹⁰ and the Belgian²² findings, but opposite to the results of the Canadian study,¹¹ which did not find significant differences in pregnancy outcomes between women with NGT and women classified as GDM by the IADPSG criteria but considered normal by the CDA. The CDA defines a single abnormal glucose value in the OGTT as gestational glucose intolerance and treats this group of patients in the same way as patients with GDM. This could explain the findings of no differences in the pregnancy outcomes between the additional IADPSG-GDM group and women with NGT in the Canadian study.¹¹ Jensen et al found that pregnant women with mild glucose intolerance, but not classified as GDM, had worse perinatal outcomes, more cesarean sections, more spontaneous preterm deliveries and more macrosomia than women with NGT.²⁴ This is consistent with the worse perinatal outcomes among the women in the additional IADPSG-GDM group in our study. Furthermore, treatment of mild GDM has been shown to improve perinatal outcomes.^25,26

However, we did not find statistically significant differences among the three groups in other clinically important outcomes such as stillbirth, neonatal death and absolute birth weight (too few observations were available to evaluate macrosomia). This could be attributed to effective treatment of GDM patients in the current study. The small sample size could be another factor explaining the lack of differences in these variables. The Belgian²² and Italian studies¹⁰ reported same findings of no differences in the birth weight and the rate of macrosomia between the three groups. However, when the latter study calculated the ponderal index for newborns, they found the reclassified GDM group by the IADPSG criteria had a higher newborn ponderal index than both the NGT and the treated GDM group.¹⁰ The ponderal index of the newborn is the ratio of weight/length cubed, and may be a more accurate measurement of fetal overgrowth than birth weight; however, this value was not calculated in our study. A recent retrospective study from Japan found the number of infants with a birthweight ≥3600 g was significantly higher among women reclassified as GDM by the IADPSG criteria, but who were formerly classified as normal by the Japan Society of Obstetrics and Gynecology criteria than among women with normal glucose.⁶ Of note, the latter two studies did not treat the additional IADPSG-GDM cases as we did, and this could explain the differences between their results and ours.

The strengths of our study include being prospective and population-based with an analysis of large amounts of data on maternal characteristics and pregnancy outcomes separately. Another important strength in the current study is that all women diagnosed with GDM were treated, unlike other studies, thus removing confounding by treatment. A limitation of the study is the relatively small numbers of subjects, which could limit the power of statistical findings.

In conclusion, the new criteria proposed by the IADPSG for diagnosing gestational diabetes identify more cases of GDM with a lesser degree of hyperglycemia than those identified by the former ADA criteria and hence increase the GDM frequency. The additional GDM cases identified by the IADPSG have clinical and metabolic characteristics resembling those women who would have GDM according to the former ADA criteria. Those women have an increased risk for adverse pregnancy outcomes compared with women with NGT. Treatment and medical follow up are warranted in this group and further studies are needed to look at the efficacy of treating this category. Larger prospective studies are needed to confirm our results. Studies on the cost effectiveness of applying the IADPSG recommendations on the screening and diagnosis of GDM are also needed.