Introduction

Pregnancy complicated by type 1 diabetes mellitus requires tight glycaemic control. Clinical guidelines include HbA1c targets for affected women [1]. A growing number of type 1 diabetic women achieve the recommended HbA1c goal; however, the prevalence of macrosomia remains high [2–4]. This may be because HbA1c, a long-term glycaemic marker, does not reflect short excursions [5]. Moreover, glucose peaks are frequently missed in the conventional self-monitoring of blood glucose (SMBG) [5]. Continuous glucose monitoring systems (CGMS) are still expensive, time-consuming and invasive [6]. An association between levels of fructosamine, a short-term glycaemic marker, and birthweight has been described in pregnant women with type 1 diabetes [7]; however, it is not widely used in clinical practice.

1,5-Anhydroglucitol (1,5-AG) is a monosaccharide, which is sometimes used as a short-term marker of glycaemic excursions, particularly postprandial ones [8]. In contrast to HbA1c, it reflects changes in glycaemic control over the preceding 1 to 2 weeks [9]. Due to its competition with other monosaccharides for reabsorption in the proximal renal tubule, the 1,5-AG excretion rate depends on the renal threshold for glucose [10]. As this threshold is decreased during pregnancy, the clinical value of using 1,5-AG to evaluate glycaemic control in pregnant women with type 1 is currently not established.

We evaluated the association of serum 1,5-AG and HbA1c with CGMS indices, as well as the performance of 1,5-AG and HbA1c levels in predicting macrosomia.

Methods

Patients

Between 2008 and 2012 we contacted 98 consecutively presenting pregnant type 1 diabetic women receiving care in the Department of Metabolic Diseases, Krakow, Poland. Of the patients contacted, 92 agreed to participate and 86 completed follow-up until delivery. Since 1,5-AG levels can be altered in chronic renal and liver diseases, we excluded two patients because of hepatic dysfunction; none of the participants had stage 3 or higher chronic kidney disease. In addition, two women who miscarried were not included. Thus, the study group consisted of 82 women whose characteristics are shown in Table 1. The protocol was approved by the Bioethical Committee of the Jagiellonian University. Written informed consent was obtained from all participants.

Table 1 Maternal and neonatal characteristics of the entire study group and subgroups defined by neonatal birthweight
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Clinical measurements

In each trimester, the serum 1,5-AG concentration was measured immuno-enzymatically with a kit (1,5-AG ELISA Kit; Cusabio, Wuhan, China). The intra- and inter-assay coefficients of variation were <1.8% and 0.9% to 4.6%, respectively. HbA1c levels were also assessed in each trimester, using high-performance liquid chromatography (Bio-Rad, Strasbourg, France). In 58 women (12, 22 and 24 in the consecutive trimesters), the results of CGMS were analysed for a 7 day period before blood collection for 1,5-AG and HbA1c measurement. Mean glycaemia, its standard deviation, mean maximum glycaemia (defined as the average daily maximum over 7 days), 7 day mean AUC above 7.8 mmol/l (AUC-7.8) and 7 day mean AUC below 3.1 mmol/l (AUC-3.1) were calculated using CGMS software (Medtronic, Minneapolis, MN, USA). Eight-point SMBG profiles were performed daily to calculate mean glucose and mean maximum glucose for the analysis of birthweight and macrosomia in the 82 pregnancies.

Statistical analysis

The association of serum 1,5-AG and HbA1c with CGMS indices, as well as the performance of 1,5-AG and HbA1c levels in predicting macrosomia, were examined. The relationship between outcomes (CGMS indices or birthweight) and predictors (1,5-AG or HbA1c) was analysed with Pearson correlations and multiple regression. We controlled for possible confounding by gestational age, pre-pregnancy BMI or maternal age. Skewed data were log-transformed. Logistic regression, receiver operating characteristic (ROC) analysis and continuous net reclassification improvement (NRI) [11] were used to evaluate 1,5-AG and HbA1c as predictors of macrosomia, defined as a neonatal birthweight >90th percentile (sex-specific) in the Polish population. Statistical calculations were performed with MedCalc 9.3.8 (MedCalc Software, Ostend, Belgium) and SAS 9.3 (SAS Institute, Cary, NC, USA). Values of p < 0.05 were considered significant.

Results

Glycemic control

The group of type 1 diabetic women examined by us had excellent glycaemic control, as defined by HbA1c targets. Mean HbA1c levels were 5.8 ± 0.9%, 5.5 ± 0.7% and 5.4 ± 0.7% (40 ± 10, 37 ± 7 and 36 ± 7 mmol/mol) in first, second and third trimesters respectively. There was no difference in mean 1,5-AG levels between consecutive pregnancy trimesters (30.0 ± 11.0, 29.4 ± 12.2, 30.0 ± 11.0 μmol/l; 4.9 ± 1.8, 4.8 ± 2 and 4.9 ± 1.8 μg/ml; p = 0.4, respectively).

Association of HbA 1c and 1,5-AG with CGMS

To evaluate 1,5-AG and HbA1c as markers of glucose levels, we used CGMS measurements from 56 women at various gestational ages. Interestingly, there was no correlation between 1,5-AG and HbA1c (r = −0.07; p = 0.57). 1,5-AG correlated strongly with CGMS-based mean glucose (r = −0.54; p < 0.001), and with a metric of glucose variability (amplitude)—standard deviation (r = 0.60; p < 0.001). In addition, 1,5-AG correlated with two metrics of hyperglycaemia: average maximum glucose (r = −0.58; p < 0.001) and AUC-7.8 (r = −0.66; p < 0.001). It did not correlate (r = 0.05, p = 0.70) with hypoglycaemia (AUC-3.1). HbA1c was weakly correlated with mean glucose (r = 0.34; p = 0.01), but not with standard deviation (r = 0.17; p = 0.23), mean maximum glucose (r = 0.2; p = 0.14), AUC-7.8 (r = 0.22; p = 0.10) and AUC-3.1 (r = −0.23; p = 0.10). The pattern of correlations was not affected when the analysis was restricted to a particular trimester. In regression models, in which CGMS indices (except AUC-3.1) were used as dependent variables, 1,5-AG was always statistically independent of HbA1c (p < 0.001 in each model).

Predicting macrosomia with 1,5-AG and HbA 1c

We subsequently evaluated 1,5-AG in 82 women as a risk marker of clinical outcome, birthweight and macrosomia. In 28 (34%) pregnancies, macrosomia was diagnosed. Interestingly, in 22 mothers of macrosomic newborns (80% of macrosomia cases) third trimester HbA1c was <6.0% (42 mmol/mol). The mean second and third trimester 1,5-AG concentrations (Table 1) were significantly lower in mothers of macrosomic babies (p = 0.001 and p < 0.001 for the second and third trimester, respectively). The correlation coefficient of 1,5-AG levels with birthweight was r = −0.44 (p < 0.001) for the second and r = −0.58 (p < 0.001) for the third trimester. The corresponding coefficients for second and third trimester HbA1c levels were 0.29 (p = 0.014) and 0.32 (p = 0.005), respectively. In the multivariate linear regression model, the 1,5-AG level, either in the second or third trimester, was associated with birthweight independently (p < 0.001) of HbA1c, after adjusting for confounders.

The third trimester 1,5-AG value, the strongest predictor of birthweight, was evaluated in logistic regression as a risk marker of macrosomia. The relative odds of macrosomia per 1 μg/ml (6.1 μmol/l) decrease in 1,5-AG was 3.0 (95% CI 1.6, 5.8; p = 0.001). In ROC analysis the AUC reached 0.81 (95% CI 0.70, 0.89). The optimum sensitivity, specificity, and corresponding positive and negative predictive values were 96.3%, 56%, 55% and 96.6%, respectively at 4.76 μg/ml (29.0 μmol/l) as cut-off value for 1,5-AG (Fig. 1). Additionally, the AUC of 1,5-AG in the second trimester was 0.75 (95% CI 0.64, 0.86). In comparison, the AUC of HbA1c in the third and second trimester was 0.69 (95% CI 0.58, 0.81) and 0.71 (95% CI 0.59, 0.83), respectively. The difference between the AUC of 1,5-AG and HbA1c (0.81 vs 0.69) was not statistically significant (p = 0.15); however, another discrimination measure, NRI [11], was 0.49 (95% CI 0.05, 0.93; p = 0.028) in favour of 1,5-AG.

Fig. 1
figure 1

ROC curve analysis for third trimester maternal 1,5-AG. (a) ROC curve illustrating the accuracy of 1,5-AG in predicting neonate macrosomia. Circle, optimum value; diagonal dotted line, the null value of ROC curve. (b) Sensitivity (black) and specificity (grey) plotted against cut-off value of 1,5-AG concentration

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Since HbA1c and 1,5-AG are independently associated with birthweight, we used the third trimester markers 1,5-AG in combination with HbA1c to predict macrosomia. This model had a substantially improved AUC of 0.84 (95% CI 0.76, 0.93), which was significantly better than HbA1c alone (p = 0.009). The NRI was 0.94 (95% CI 0.56, 1.31; p < 0.001). The addition of second trimester markers, maternal age and BMI did not alter the results and did not significantly improve prediction. Using the predictive score derived from the model variables 1.2 × (HbA1c [%]) − (1,5-AG [μg/ml]) or (HbA1c [mmol/mol]) − 1.5 × (1,5-AG [μmol/l]), we obtained optimum sensitivity, specificity, and positive and negative predictive values of 85.7%, 71.4%, 63.2% and 89.7%, respectively, where score values ≥2.14 (or ≥−4.13, when molar concentrations are used) indicated risk of macrosomia with relative odds of 2.8 (95% CI 1.6, 4.8; p < 0.001).

Discussion

In our study of pregnant women with type 1 diabetes mellitus, levels of 1,5-AG, a short-term glycaemic marker that, unlike HbA1c, captures episodes of hyperglycaemia, were strongly correlated with indices derived from CGMS. The observed negative correlations between 1,5-AG levels and CGMS metrics are in agreement with earlier studies involving non-pregnant diabetic participants [8]. It has also been previously shown that HbA1c levels did not correlate well with maternal glucose profiles measured with CGMS [5]. This seems to explain the high rate of adverse pregnancy outcomes observed earlier [2–4] and in this study, despite patients achieving the recommended HbA1c values.

This finding could be of clinical importance, as we have shown for the first time that 1,5-AG provides insight into short-term glycaemic control in pregnant women with type 1 diabetes. Its use may improve the assessment of whether insulin dosage modifications are necessary, eventually helping improve pregnancy outcomes. Currently, patients with type 1 diabetes are mainly monitored by daily SMBG in combination with HbA1c. 1,5-AG, which responds rapidly to changes in glucose profile, may facilitate treatment adjustments, providing an accurate, rapid, possibly cost-effective and practical additional or even alternative tool to HbA1c, and one that probably would also be more reliable and objective than SMBG.

Another new finding was that third trimester 1,5-AG levels appeared to be a strong predictor of macrosomia and, as indicated by AUC values in ROC analysis, performed better than HbA1c. It should be noted that most mothers of macrosomic babies met HbA1c-based criteria of glycaemic control. The high risk of macrosomia in such patients may be explained by glucose excursions that were undetected with HbA1c, but were reflected in their 1,5-AG levels. Indeed, 1,5-AG was strongly associated with CGMS AUC-7.8, standard deviation and average maximum glycaemia. 1,5-AG could therefore be a particularly suitable marker in patients achieving HbA1c targets. Although 1,5-AG singly was superior to HbA1c in predicting risk of macrosomia, even better results were achieved when both markers were used jointly. Since 1,5-AG and HbA1c were uncorrelated, the best discriminative accuracy was achieved when information from both these markers was combined in the proposed risk index. A possible shortcoming of our study is that two short-term measures, 1,5-AG and CGMS, were analysed together with a long-term measure, HbA1c. In addition, the difference in the prediction power of macrosomia risk between 1,5-AG and HbA1c was rather moderate. Future clinical studies targeting HbA1c and 1,5-AG therapeutic goals in pregnant women with type 1 diabetes would be of tremendous interest.

In spite of earlier concerns [10] that the decreased renal threshold for glucose in pregnancy might lower the 1,5-AG level and potentially decrease its ability to differentiate well- and poorly controlled diabetes, 1,5-AG in our study appeared to be a very good marker of glycaemia in pregnant women with type 1 diabetes. During pregnancy, our patients achieved excellent glycaemic targets, which would have acted in the opposite direction to that of an altered renal threshold, i.e. by increasing the 1,5-AG level. Eventually, 1,5-AG remained very sensitive to hyperglycaemia. Its performance in pregnant women with other types of diabetes, who may differ not only by the degree of metabolic control but also in terms of glycaemic fluctuations, requires further evaluation.

In summary, 1,5-AG performs better than HbA1c as a tool for monitoring the glucose profile in pregnancies complicated by type 1 diabetes. Its decreased third trimester level is a very valuable predictor of macrosomia, particularly considered together with HbA1c. The determination of 1,5-AG should be considered for clinical use in type 1 diabetic pregnancies.