Abstract
Objectives
To determine the incidence of overt diabetes in pregnancy (ODIP) among women with 50-g GCT results ≥ 200 mg/dL and compare characteristics and pregnancy outcomes between women with and without gestational diabetes (GDM).
Methods
A retrospective cohort study was conducted in 212 pregnant women whose 50-g GCT results ≥ 200 mg/dL. ODIP was diagnosed from 75-g OGTT if fasting plasma glucose ≥ 126 and/or 2-h plasma glucose ≥ 200 mg/dL. Various characteristics and pregnancy outcomes were compared between ODIP and those with and without GDM.
Results
Incidence of ODIP was 1.9% of all pregnant women and 23.6% of women with 50-g GCT ≥ 200 mg/dL. Women with ODIP and GDM were more likely to be overweight or obese than those without GDM (52%, 39.6%, and 18.2%, p < 0.001). Women with ODIP had significantly higher 50-g GCT results, lower gestational weight gain, and were less likely to deliver vaginally. Insulin therapy was significantly more common in women with ODIP compared to GDM (70.2% vs. 15.4%, p < 0.001). Rates of LGA, macrosomia, and other neonatal outcomes were comparable. BMI ≥ 25 kg/m2 and 50-g GCT ≥ 240 mg/dL independently increased the risk of any abnormal glucose tolerance [adjusted OR 3.22 (95% CI 1.55–6.70) and 2.28 (95% CI 1.14–4.58)] and ODIP [adjusted OR 9.43 (95% CI 2.15–41.38) and 6.36 (95% CI 2.85–14.18)], respectively.
Conclusion
Incidence of ODIP was 23.6% of women with 50-g GCT ≥ 200 mg/dL. BMI ≥ 25 kg/m2 and 50-g GCT ≥ 240 mg/dL independently increased the risk of GDM and ODIP. Neonatal complications were comparable between ODIP and those with and without GDM.
Keywords: Overt diabetes in pregnancy, 50-g glucose challenge test, 75-g OGTT, Pregnancy outcomes
Introduction
Gestational diabetes (GDM) is defined as any degree of glucose intolerance that was first recognized during pregnancy. [1–4] However, the diagnosis is made regardless of the degree of hyperglycemia so women with a more severe degree of hyperglycemia or even those with undiagnosed diabetes might also be included. Several organizations have raised the importance of classifying these women with a more severe form of hyperglycemia separately from GDM since the condition could be associated with worse pregnancy outcomes and warrants an aggressive management and follow-up approach. [1–5]
When the level of hyperglycemia first detected during pregnancy meets the standard diagnostic criteria for diabetes in nonpregnant women, the condition can be called “overt diabetes in pregnancy”, “diabetes in pregnancy”, or “diabetes complicating pregnancy”. [1–3, 5, 6] Those criteria are fasting plasma glucose (FPG) ≥ 126 mg/dL, and/or a 2-h 75-g oral glucose tolerance test (OGTT) value ≥ 200 mg/dL. [2–4, 6]
Women with overt diabetes in pregnancy (ODIP), as well as undiagnosed diabetes, have been reported to have comparable adverse outcomes as those with pre-gestational diabetes, including an increase in preterm birth, large for gestational age (LGA), and perinatal morbidity and mortality. [7–10] In addition, previous studies have reported that women with ODIP were at increased risk for various adverse pregnancy outcomes compared to women with GDM, including preterm birth, cesarean section (CS), preeclampsia, the need for insulin therapy, LGA, and perinatal mortality. [10–14] A previous study also reported that the adverse pregnancy outcomes of women with ODIP were comparable to those with GDM when they received aggressive glycemic management. [15]
According to institutional practice guideline in Siriraj Hospital, a 50-g glucose challenge test (GCT) and a 100-g oral glucose tolerance test (OGTT) are used for GDM screening, and those with a high 50-gGCT of ≥ 200 mg/dL are diagnosed with GDM, and treatment is immediately initiated. However, these women have been shown to have an increase risk of insulin therapy and are usually at higher risk of diabetes-related adverse pregnancy outcomes. [16, 17] It is, therefore, possible that some of these women could actually have pre-gestational diabetes, or ODIP. However, the use of 100-g OGTT would not be able to diagnose the condition. Therefore, a 75-g OGTT has been adopted for further testing among this group of women in order to correctly classify the women into 3 distinct groups, i.e., no GDM, GDM, and ODIP, which could help in better care and management to minimize maternal and fetal risks.
The primary objective of this study was to determine the incidence of ODIP among women with a high 50-g GCT of ≥ 200 mg/dL. In addition, characteristics and pregnancy outcomes were compared between women with and without GDM and ODIP. In addition, possible associated factors for abnormal glucose tolerance (GDM or ODIP) and For ODIP were investigated. The results could help improve the care of these high-risk pregnant women and minimize diabetes-related pregnancy complications in the future.
Methods
After the approval of the Siriraj Institutional Review Board (SIRB), a retrospective cohort study was conducted in 212 pregnant women who received GDM screening and had a 50-g GCT of ≥ 200 mg/dL. According to the current institutional guideline, GDM screening is offered to all pregnant women during their first antenatal visit using a 50-g GCT and a 100-g OGTT. The tests are repeated during 24–28 weeks of gestation if the initial results are normal. [18]
However, it was observed from previous studies that GDM women whose 50-g GCT were ≥ 200 mg/dL differed significantly from those with 50-g GCT of < 200 mg/dL, including baseline characteristics, pregnancy outcomes, and rate of insulin therapy. [16, 17] This could be due to the inclusion of undiagnosed overt diabetes in pregnancy cases. Therefore, in 2022, as part of the quality improvement process, if the results of the 50-g GCT are ≥ 200 mg/dL, the women will be offered a 75-g OGTT instead of a standard 100-g OGTT in order to identify women with overt diabetes in pregnancy. The use of 75-g OGTT with plasma glucose determination at 0, 1, and 2 h would help classify the women into 3 separate groups, i.e., without GDM, GDM, and ODIP. [2–4, 6] Other women with 50-g GCT of < 200 mg/dL were managed according to the conventional guideline. If 50-g GCT was 140–199 mg/dL, a 100-g OGTT was offered to diagnose GDM using Carpenter and Coustan criteria. Women with a 50-g GCT of < 140 mg/dL or a normal 100-g OGTT were re-tested during 24–28 weeks of gestation.
Singleton pregnant women who started antenatal care before 20 weeks of gestation and received GDM screening according to institutional guideline were eligible. Those with pre-gestational diabetes, fetal anomalies, or deaths were excluded. The sample size was estimated from the 20% incidence of diabetes in pregnancy among pregnant women whose 50-g GCT result was ≥ 200 mg/dL. At least 206 pregnant women are needed, with a 6% acceptable error including a 20% loss.
Medical records of the women were retrieved, and data were extracted, including baseline and obstetric characteristics, GDM screening results and final diagnosis, antenatal care, and delivery data. Pre-pregnancy body mass index (BMI) and gestational weight gain were categorized according to the Institute of Medicine recommendations. [19] The diagnosis of overt diabetes in pregnancy (ODIP) and GDM were based on 75-g OGTT results. The criteria for diagnosis of ODIP are as follows: fasting plasma glucose (FPG) ≥ 126 mg/dL, and/or a 2-h 75-g oral glucose tolerance test (OGTT) value ≥ 200 mg/dL. [2–4, 6] GDM is diagnosed according to IADPSG criteria. [6]
Antenatal and intrapartum care were provided by attending obstetricians following institutional guideline. Women with ODIP and GDM were initially provided with individual counseling and nutritional therapy with close follow up of FPG and/or 2-h postprandial plasma glucose with glycemic targets of < 95 and < 120 mg/dL. Those with ODIP were also sent to endocrinologists for consultation. HbA1c was not routinely evaluated as per the current guideline. Insulin therapy was initiated if glycemic control with nutritional therapy was inadequate, at the discretion of obstetricians or endocrinologists.
Data on pregnancy outcomes, including the need for insulin therapy, gestational age at delivery, route of delivery, birth weight, preeclampsia, and postpartum hemorrhage. Gestational weight gain was calculated from the difference between weight at delivery and pre-pregnancy weight and categorized according to pre-pregnancy BMI categories as recommended by the Institute of Medicine. [19] Preterm birth was defined as birth before 37 complete gestational weeks. Preeclampsia was defined as the new onset of hypertension after 20 weeks of gestation, accompanied by significant proteinuria or abnormalities from other laboratory tests or clinical results of organ damage. [20] Large for gestational age (LGA) and small for gestational age (SGA) was defined as an infant’s birth weight of > 90th and < 10th percentiles for gestational age based on the WHO weight percentile calculator. [21] Low birth weight was defined as a birth weight of < 2500 g. Macrosomia was defined as an infant’s birth weight of ≥ 4 kg.
Mean, standard deviation, number, and percentage were used to described various characteristics as appropriate. Analysis of variance (ANOVA) with Tukey post-hoc comparison and chi square tests were used to compare baseline characteristics and pregnancy outcomes between women without GDM, GDM, and ODIP. Univariate and multivariate logistic regression analyses were performed to determine association between various clinical characteristics and the risk for abnormal glucose tolerance (GDM or ODIP) and ODIP. Relative risks (RR) and adjusted odds ratios (OR) were estimated with corresponding 95% confidence intervals (CI). A p value of < 0.05 was considered statistically significant.
Results
During January to October 2022, a total of 2671 pregnant women received GDM screening, and 212 women had 50-g GCT ≥ 200 (8.1%) and further received 75-g OGTT. Baseline characteristics of the women are reported in Table 1. The mean age was 32.9 years, the mean BMI was 24.3 kg/m2, and 52.4% were nulliparous. As many as 35.9% of the women were overweight or obese. Approximately half (52.8%) of the women had at least 1 risk factor for GDM, and most common risks were age ≥ 30 years (71.1%), overweight or obesity (35.8%), and DM in family (19.3%).
Table 1.
Baseline characteristics of the pregnant women (N = 212)
| Characteristics | N (%) |
|---|---|
| Mean age ± SD (years) | 32.9 ± 5.4 |
| Mean BMI ± SD (kg/m2) | 24.3 ± 5.7 |
| Nulliparous | 111 (52.4) |
| BMI category | |
| Underweight | 24 (11.3) |
| Normal | 112 (52.8) |
| Overweight | 37 (17.5) |
| Obese | 39 (18.4) |
| GDM risk | |
| Age ≥ 30 years | 152 (71.1) |
| DM in family | 41 (19.3) |
| BMI ≥ 25 kg/m2 | 76 (35.9) |
| Previous GDM | 22 (10.4) |
| Previous macrosomia | 2 (0.9) |
| Hypertension | 10 (4.7) |
| Any GDM risk | 112 (52.8) |
Characteristics of GDM screening and diagnosis are displayed in Table 2. The mean GA at screening was 11.9 weeks of gestation. The mean 50-g GCT was 224.6 mg/dL. After 75-g OGTT, 50 women (23.6%) were diagnosed as having ODIP, 96 (45.3%) had GDM, and 66 (31.1%) had normal results. ODIP accounted for 1.9% of all pregnant women (50 of 2671 women). Among 50 women with ODIP, 10 (20%) had FPG ≥ 126 mg/dL only, 28 (56%) had 2-h plasma glucose ≥ 200 mg/dL only, and 12 (24%) had both abnormal results. Data on HbA1c was available in 15 women with a mean value of 5.8%. Of them, 2 (13.3%) had HbA1c ≥ 6.5%, corresponding with the diagnosis of pre-gestational DM. Of those with normal initial screening, 5 of 66 women (7.6%) were diagnosed with GDM during 24–28 weeks of gestation.
Table 2.
Characteristics of GDM screening and diagnosis
| Characteristics | N (%) |
|---|---|
| Mean GA at screening ± SD (weeks) | 11.9 ± 6.8 |
| Mean 50-g GCT ± SD (mg/dL) | 224.6 ± 27.5 |
| Diagnosis | |
| No GDM | 66 (31.1) |
| GDM | 96 (45.3) |
| Overt diabetes in pregnancy | 50 (23.6) |
| Among overt diabetes in pregnancy (N = 50) | |
| FPG ≥ 126 mg/dL only | 10 (20) |
| 2-h plasma glucose ≥ 200 mg/dL only | 28 (56) |
| FPG ≥ 126 mg/dL and 2-h plasma glucose ≥ 200 mg/dL | 12 (24) |
| HbA1c (N = 15) | |
| Mean HbA1c at diagnosis ± SD (%) | 5.8 ± 0.9 |
| HbA1c ≥ 6.5% | 2 (13.3) |
Comparisons between the 3 groups with regard to various characteristics were performed, and the results are shown in Table 3. Women without GDM had a significantly lower BMI than the other 2 groups (p < 0.001). Overweight or obesity were found in 39.6% and as many as 42% of women with GDM and ODIP, respectively (p < 0.001). No other GDM risk was associated with GDM or ODIP. However, both GDM and ODIP were significantly more likely to have at least 1 GDM risk factor (59.4% and 68%, respectively, p < 0.001). Women with ODIP had significantly higher 50-g GCT results than the other 2 groups (p < 0.001). Almost all the women without GDM had 50-g GCT of < 240 mg/dL (97%), compared to 85.4% in GDM and 60% in ODIP (p < 0.001). It can also be observed that if 50-g GCT cutoff at ≥ 240 mg/dL was used, 34 of 36 (94.4%) of the women would have GDM or ODIP and 20 of 36 (55.6%) would have ODIP.
Table 3.
Comparison of characteristics between the 3 groups
| Characteristics | No GDM N = 66 |
GDM N = 96 |
ODIP N = 50 |
P value |
|---|---|---|---|---|
| Mean age ± SD (years) | 31.7 ± 5.8 | 33.8 ± 5.2 | 32.9 ± 5.0 | 0.054 |
| Mean BMI ± SD (kg/m2) | 21.9 ± 4.7a | 24.6 ± 5.0 | 26.9 ± 6.9 | < 0.001 |
| Mean 50-g GCT ± SD (mg/dL) | 214.9 ± 11.9 | 221.1 ± 16.5 | 244.2 ± 44.8b | < 0.001 |
| 50-g GCT levels | < 0.001 | |||
| < 240 mg/dL | 64 (97%) | 82 (85.4%) | 30 (60%) | |
| ≥ 240 mg/dL | 2 (3%) | 14 (14.6%) | 20 (40%) | |
| Nulliparous | 35 (53.0%) | 49 (51.0%) | 27 (54.0%) | 0.936 |
| BMI category | < 0.001 | |||
| Underweight | 17 (25.8%) | 7 (7.3%) | 0 (0%) | |
| Normal | 37 (56.1%) | 51 (53.1%) | 24 (48.0%) | |
| Overweight | 7 (10.6%) | 21 (21.9%) | 9 (18.0%) | |
| Obese | 5 (7.6%) | 17 (17.7%) | 17 (34.0%) | |
| GDM risk | ||||
| Age ≥ 30 years | 43 (65.2%) | 74 (66.1%) | 35 (70.0%) | 0.242 |
| DM in family | 10 (15.2%) | 18 (18.8%) | 13 (26.0%) | 0.335 |
| BMI ≥ 25 kg/m2 | 12 (18.2%) | 38 (39.6%) | 26 (52%) | < 0.001 |
| Previous GDM | 4 (6.1%) | 14 (14.6%) | 4 (8.0%) | 0.178 |
| Previous macrosomia | 0 (0%) | 1 (1.0%) | 1 (2.0%) | 0.539 |
| Hypertension | 1 (1.5%) | 7 (7.3%) | 2 (4.0%) | 0.226 |
| Any GDM risk | 21 (31.8%) | 57 (59.4%) | 34 (68.0%) | < 0.001 |
aSignificantly lower than GDM (p < 0.001) and ODIP (p = 0.007)
bSignificantly higher than women with and without GDM (p < 0.001)
Pregnancy outcomes were available in 166 women (11 had early fetal losses, and 35 were lost to follow up or delivery at other hospitals). Comparisons between the 3 groups are shown in Table 4. Women with ODIP had significantly lower gestational weight gain than the other 2 groups (p < 0.001), and 22 (61.1%) gained weight less than the recommendation. However, it should be noted that 27.8% still had excessive gestational weight gain. Insulin therapy was also significantly more common in women with ODIP compared to those with GDM (70.2% vs. 15.4%, p < 0.001). Those with ODIP were less likely to deliver vaginally than others (p = 0.041). Preterm birth and preeclampsia were slightly more common in GDM and diabetes in pregnancy without statistical significance. Rates of SGA, low birth weight, LGA, macrosomia, neonatal hypoglycemia, and NICU admission were comparable between groups. No congenital anomalies were observed.
Table 4.
Comparison of Pregnancy outcomes between the 3 groups
| Characteristics | No GDM N = 53 |
GDM N = 77 |
ODIP N = 36 |
P value |
|---|---|---|---|---|
| Mean GA at delivery ± SD (weeks) | 38.0 ± 1.5 | 37.6 ± 1.4 | 37.3 ± 1.5 | 0.079 |
| Mean GWG ± SD (kg) | 12.7 ± 5.1 | 10.5 ± 5.5 | 6.5 ± 6.5a | < 0.001 |
| Mean birth weight ± SD (kg) | 3.06 ± 0.44 | 3.04 ± 0.55 | 2.97 ± 0.55 | 0.702 |
| GWG category | 0.004 | |||
| Lower than recommendation | 15 (28.3%) | 32 (41.6%) | 22 (61.1%) | |
| Normal | 25 (47.2%) | 31 (40.3%) | 4 (11.0%) | |
| Excessive | 13 (24.5%) | 14 (18.2%) | 10 (27.8%) | |
| Insulin therapyb | - | 14/91 (15.4%) | 33/47 (70.2%) | < 0.001 |
| Preterm birth | 6 (11.3%) | 11 (14.3%) | 7 (19.4%) | 0.563 |
| Route of delivery | 0.041 | |||
| Vaginal delivery | 28 (52.8%) | 33 (42.9%) | 10 (27.8%) | |
| Primary CS | 14 (26.4%) | 24 (31.2%) | 20 (55.6%) | |
| Repeat CS | 11 (20.8%) | 20 (26.0%) | 6 (16.7%) | |
| Low birth weight (< 2500 g) | 3 (5.5%) | 8 (10.7%) | 5 (13.9%) | 0.378 |
| SGA | 6 (10.9%) | 7 (9.3%) | 3 (8.3%) | 0.914 |
| LGA | 17 (32.1%) | 27 (35.1%) | 12 (33.3%) | 0.986 |
| Macrosomia | 2 (3.8%) | 1 (1.3%) | 1 (2.8%) | 0.656 |
| Preeclampsia | 2 (3.8%) | 8 (10.4%) | 4 (11.1%) | 0.332 |
| Postpartum hemorrhage | 4 (7.5%) | 4 (5.2%) | 4 (11.1%) | 0.542 |
| Neonatal hypoglycemia | 1 (1.9%) | 3 (3.9%) | 3 (8.3%) | 0.326 |
| NICU admission | 1 (1.9%) | 2 (2.6%) | 2 (5.6%) | 0.585 |
asignificantly lower than no GDM (p < 0.001) and GDM (p = 0.002)
b3 and 5 women in GDM and ODIP had fetal loss before any treatment and were excluded
Table 5 shows the results of univariate and multivariate analyses to determine possible associated risk factors for any abnormal glucose tolerance (GDM or ODIP) and ODIP. Both BMI ≥ 25 kg/m2 and 50-g GCT ≥ 240 mg/dL were found to be significantly and independently associated with the diagnosis of GDM or ODIP. After adjusting for potential confounders, BMI ≥ 25 kg/m2 independently increased the risk of any abnormal glucose tolerance and ODIP with adjusted OR 3.22 (95% CI 1.55–6.70) and 9.43 (95% CI 2.15–41.38), respectively. High 50-g GCT ≥ 240 mg/dL also independently increased the risk of any abnormal glucose tolerance and ODIP with adjusted OR 2.28 (95% CI 1.14–4.58) and 6.36 (95% CI 2.85–14.18), respectively.
Table 5.
Evaluation of associated risk factors for GDM and/or ODIP by univariate and multivariate analyses
| Risk factors | Univariate analysis | Multivariate analysis | |||
|---|---|---|---|---|---|
| RR (95%CI) | P value | Adjusted OR (95%CI) | P value | ||
| GDM or ODIP | |||||
| BMI ≥ 25 kg/m2 | 1.40 (1.18–1.65) | < 0.001 | 3.22 (1.55–6.70) | 0.002 | |
| 50-g GCT ≥ 240 mg/dL | 1.48 (1.29–1.70) | < 0.001 | 9.43 (2.15–41.38) | 0.003 | |
| ODIP | |||||
| BMI ≥ 25 kg/m2 | 1.94 (1.20–3.13) | 0.003 | 2.28 (1.14–4.58) | 0.020 | |
| 50-g GCT ≥ 240 mg/dL | 3.26 (2.10–5.05) | < 0.001 | 6.36 (2.85–14.18) | < 0.001 | |
Adjusted for parity, age ≥ 30 years, DM in family, and previous GDM
Discussion
As diabetes screening is not widely performed among non-pregnant women of reproductive age or routinely included in pre-marital or pre-pregnancy counseling and evaluation, some women become pregnant with undiagnosed diabetes. If these women were not diagnosed appropriately, the risks of adverse maternal and neonatal outcomes could significantly increase. Correct identification of pregnant women with a greater degree of hyperglycemia will lead to timely and appropriate management to minimize maternal and fetal risks.
The results of this study showed that the incidence of ODIP among women with a 50-g GCT ≥ 200 mg/dL was 23.6%, corresponding to 1.9% of all pregnant women. The estimated incidence could probably be underestimated since those whose 50-g GCT was < 200 mg/dL did not receive 75-g OGTT, that some women with ODIP were not diagnosed. The incidence of ODIP reported in other previous studies varied from 1.4% to 4% of all pregnant women, depending on the population included and definitions. [13, 15] Previous studies reported that ODIP contributed to 13–21.5% of all GDM cases, which was lower than in the current study. [10, 13, 14] This could be due to the inclusion of women with a higher risk of ODIP in this study, i.e., those with a 50-g GCT ≥ 200 mg/dL. Another study reported that ODIP was found in 33% of women with overt and pre-gestational diabetes. [7] Although it cannot be differentiated between ODIP and pre-gestational diabetes, with the early gestational age at diagnosis in this study, these women could possibly have undiagnosed pre-gestational diabetes.
A greater severity of hyperglycemia was observed among women with ODIP than GDM, as demonstrated by a higher 50-g GCT level and a higher rate of insulin therapy. Previous studies also reported similar findings that women with ODIP were more likely to require insulin therapy at a higher dose compared to those with GDM. [10, 12, 14] The findings also support that this group of women could have had undiagnosed diabetes before pregnancy. The relationship between the greater severity of abnormal 50-g GCT results and the risk of ODIP has also been observed. The results showed that when 50-g GCT was ≥ 240 mg/dL, 94.4% of the women had either GDM or ODIP and 55.6% had ODIP. In multivariate analysis, 50-g GCT ≥ 240 mg/dL independently increased the risk of having any abnormal glucose tolerance (GDM or ODIP) and ODIP by 9.43 and 6.36 times, respectively.
Although the use of 100-g OGTT for GDM diagnosis can potentially identify some women with ODIP (i.e., FPG ≥ 126 mg/dL), other cases would still go undiagnosed. As demonstrated in this study, 56% of ODIP would have been missed if only FPG of 100-g OGTT was used for diagnosis. Moreover, if 75-g OGTT was not used, 31.1% of the women would have been diagnosed and unnecessarily treated as having GDM according to the previous guideline. These support the value of the use of 75-g OGTT among these high-risk women to correctly classify them and provide more appropriate management in a timely fashion.
As expected, overweight and obesity were shown to be associated with an increased risk of both GDM and ODIP, and as many as 39.6% and 52% of women with GDM and ODIP were overweight or obese, respectively. In multivariate analysis, pre-pregnancy overweight or obesity (BMI ≥ 25 kg/m2) independently increased the risk of having any abnormal glucose tolerance (GDM or ODIP) and ODIP by 3.22 and 2.28 times, respectively. Similar results have been reported in previous studies. [10, 14] Being overweight or obese has been well recognized as one of the important risks for GDM and diabetes in the general population. [1–3] The risks could be lowered by appropriate pre-pregnancy evaluation and counseling regarding BMI status and weight control interventions.
Women with ODIP had a significant lower GWG than the other 2 groups, which could be the result of more intensive care and counseling by both obstetricians and endocrinologists following the same guideline. Moreover, information on GWG was routinely provided to every pregnant woman early in pregnancy and was monitored closely in every visit for GDM and ODIP cases. The differences in the rates of insulin therapy could be due to the different degrees of hyperglycemia between ODIP and GDM. However, it also depended on the different judgements of caring physicians, i.e., obstetricians in GDM cases and endocrinologists in ODIP cases.
It was demonstrated in previous studies that women with ODIP were at increased risk for various adverse pregnancy outcomes similar to those with pre-gestational diabetes, including preterm birth, LGA, and perinatal morbidity and mortality. [7–9] Moreover, most previous studies also showed that adverse pregnancy outcomes were also increased among women with ODIP compared to those with GDM, including preterm birth, cesarean section, preeclampsia, the need for insulin therapy, LGA, and perinatal mortality. [10–13]
However, the results of this study showed that pregnancy outcomes were comparable between women with ODIP and those with and without GDM regarding preterm birth, preeclampsia, LGA, macrosomia, neonatal hypoglycemia, and NICU admission. The insignificant differences might partly be due to the limited number of cases with ODIP in this study. In terms of fetal overgrowth, the results could be partly explained by the significantly lower gestational weight gain observed among ODIP group, which could be due to intensive glycemic control with nutritional and insulin therapy provided. This is also consistent with the results of a previous study, which reported that the adverse pregnancy outcomes of women with ODIP were comparable to those with GDM when they received aggressive glycemic management. [15]
The strength of this study might include that it was the first in Thailand to apply the use of 75-g OGTT to diagnose ODIP in high-risk women in settings where a 2-step 50-g GCT and 100-g OGTT are used. A similar strategy can be applied to other settings with a similar GDM screening approach, and the cutoff value of 50-g GCT could be adjusted to fit the local context. Some limitations included that HbA1c was available in only 30% of ODIP cases (15 of 50) and that the proportion of pre-gestational DM could not be accurately determined. Data on postpartum DM screening was also not available. The incidence of ODIP could be underestimated, as not all women received 75-g OGTT. Although the relationship between abnormal 50-g GCT levels and ODIP has been observed, there was no information on the results of 75-g OGTT in those with 50-g GCT < 200 mg/dL, with and without 100-g OGTT results. This could deviate the observed relationship in either direction and need to be further explored in detail. The relatively small samples in each subgroup could make comparisons less reliable, so interpretation should be made cautiously. However, the results still demonstrated similar trends with regard to various characteristics and pregnancy outcomes to those of other previous studies. In addition, generalization of the results could be limited to other settings with different GDM risks and strategies for screening and diagnosis.
The clinical benefits of adopting 75-g OGTT among women with high 50-g GCT of ≥ 200 mg/dL in this study might include the early identification of ODIP so that appropriate management could be initiated in a timely manner to reduce the risk of adverse outcomes. The use of this strategy would be more cost-effective in identifying ODIP when performed on women at high risk than their lower-risk counterparts. Moreover, this can be easily adapted and applied to other settings where a similar 2-step approach is used. Understanding the associated risk factors would also help in further developing or modifying screening and diagnostic strategies that are suitable for each setting.
Further, larger studies are still needed to explore the appropriate means for diagnosis of ODIP as well as evaluate management interventions to minimize adverse perinatal outcomes. Moreover, the cost-effectiveness of these interventions is yet to be evaluated. However, it is strongly suggested that diabetes screening should be included as part of pre-marital and pre-pregnancy counseling and evaluation in order to early diagnose the condition and provide appropriate management.
In conclusion, ODIP was prevalent among women with 50-g GCT ≥ 200 mg/dL and associated with an increase in insulin therapy. Many adverse pregnancy outcomes were only slightly increased. Women with abnormally high 50-g GCT results should be screened for ODIP for appropriate and timely management to reduce the risk of adverse pregnancy outcomes. Further studies on various related issues are still needed to explore the condition in more detail. Modifications of existing guideline should be considered, especially where a standard 2-step approach is used.
Author contributions
All authors contributed to the study conception and design. AR and DG were responsible for data collection under supervision of DB. DB analyzed the data and all the authors interpreted the results together. AR and DG drafted the manuscript and DB critically revised the manuscript. All the authors approved and agreed with this final version of the manuscript. All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and/or with the Helsinki Declaration of 1964 and later versions. Informed consent or substitute for it was obtained from all patients for being included in the study.
Data availability
The data that support the findings of this study are available on request from the corresponding author.
Declarations
Conflict of interest
None.
Research involving human participants and/or animals
The study was approved by Siriraj Institutional Review Board (COA no. Si 632/2022; approval date August, 31 2022).
Informed consent
Informed consent was not obtained from the participants due to retrospective nature of data collection.
Footnotes
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data that support the findings of this study are available on request from the corresponding author.