Circadian variation of serum glucose, C-peptide immunoreactivity and free insulin normal and insulin-treated diabetic pregnant subjects

Management of Gestational Diabetes Mellitus

Once a woman is diagnosed with gestational diabetes mellitus (GDM), two strategies are considered for management; life-style modifications and pharmacological therapy. The management of GDM aims to maintain a normoglycemic state and to prevent excessive weight gain in order to reduce maternal and fetal complications. Lifestyle modifications include nutritional therapy and exercise. Calorie restriction with a low glycemic index diet is recommended to avoid postprandial hyperglycemia and to reduce insulin resistance. Blood glucose levels, HbA1c levels, and ketonuria are monitored to analyze the efficacy of conservative management. Pharmacological treatment is initiated if conservative strategies fail to provide expected glucose levels during follow-ups.Insulin has been the first choice for the treatment of diabetes during pregnancy. Recently, metformin has been used more commonly in diabetic pregnant women in cases when insulin cannot be prescribed, after its safety has been proven. However, a high percentage of women, which may be up to 46% may require additional insulin to maintain expected blood glucose levels. The evidence on the long-term safety of other oral anti-diabetics has been lacking yet.Women with diet-controlled GDM can wait for spontaneous labor expectantly in case there are no obstetric indications for birth. However, in women with GDM under insulin therapy or with poor glycemic control, elective induction at term is recommended by authorities.The women who have GDM during pregnancy should be counseled about their increased risks of impaired glucose tolerance, type 2 diabetes mellitus, hypertensive disorders, cardiovascular diseases, and metabolic syndrome.

Glycemic targets in pregnancies affected by diabetes: historical perspective and future directions

The definition of optimal glycemic control in pregnancies affected by diabetes remains enigmatic. Diabetes phenotypes are heterogeneous. Moreover, fetal macrosomia insidiously occurs even with excellent glycemic control. Current blood glucose (BG) targets (FBG ≤95, 1-h post-prandial <140, 2 h <120 mg/dL) have improved perinatal outcomes, but arguably they have not normalized. The conventional management approach has been to replicate a pattern of glycemia in normal pregnancy. Although these patterns are lower than previously appreciated, a randomized controlled trial (RCT) has never compared current vs. lower glucose targets powered on maternal/fetal outcomes. This paper provides historical context to the current targets by reviewing evidence supporting their evolution. Using lower targets (FBG <90, 1 h <122, 2 h <110, mean BG ≤95 mg/dL) may help normalize outcomes, but phenotypic differences (type 1 vs. type 2 vs. gestational diabetes) might require different glycemic goals. There remains a critical need for well-designed RCTs to confirm optimal glycemic control that minimizes both small for and large for gestational age across pregnancies affected by diabetes.

Gestational diabetes mellitus

BACKGROUND

Gestational diabetes mellitus, defined as diabetes diagnosed during pregnancy that is not clearly overt diabetes, is becoming more common as the epidemic of obesity and type 2 diabetes continues. Newly proposed diagnostic criteria will, if adopted universally, further increase the prevalence of this condition. Much controversy surrounds the diagnosis and management of gestational diabetes.

CONTENT

This review provides information regarding various approaches to the diagnosis of gestational diabetes and the recommendations of a number of professional organizations. The implications of gestational diabetes for both the mother and the offspring are described. Approaches to self-monitoring of blood glucose concentrations and treatment with diet, oral medications, and insulin injections are covered. Management of glucose metabolism during labor and the postpartum period are discussed, and an approach to determining the timing of delivery and the mode of delivery is outlined.

SUMMARY

This review provides an overview of current controversies as well as current recommendations for gestational diabetes care.

Pregnancy in Type 1 Diabetes Mellitus: How Special are Special Issues?

India leads the world with largest number of diabetics earning the dubious distinction of "the diabetes capital of the world." Diabetes is associated with maternal and perinatal morbidity and mortality. The number of pregnant women with pre-existing diabetes is increasing, mainly from an increase in type 2 diabetes, but also an increase in type 1 diabetes. Overall, type 1 diabetes accounts for approximately 5% to 10% of all diabetes outside of pregnancy, and in pregnancy put together with type 2 account for 10% of diabetic pregnancies. Management of the pregnant diabetic woman is a complex task that ideally begins before conception. Specific attention is required for diabetic pregnancies in different trimesters of pregnancy. Diabetes, especially type 1 diabetes, can be a challenge in pregnancy, but with education, close monitoring, and latest therapeutic modalities, these women can have healthy newborns. Close attention to diet, glycemic control, metabolic stresses, and early diagnosis and monitoring of complications can make pregnancy a successful experience for women with diabetes. A MedLine search was done to review relevant articles in English literature on diabetes and pregnancy, and specific issues related to pregnancy in type 1 diabetes were reviewed.

Distinctions between islet neogenesis and β-cell replication: implications for reversal of Type 1 and 2 diabetes

The terms "islet" and "β-cell" are often used interchangeably, yet islets are highly complex multicellular organelles that contain the insulin-producing β-cells and four other cells types, all of which play a role in maintaining glucose homeostasis within a very narrow range. Although the formation of new islets in adults is rare, occurring primarily in response to pancreatic injury and major stress to the pancreas, β-cell replication from existing cells occurs throughout adulthood. An understanding of the regulatory factors controlling pancreatic development has more clearly defined the differences between new islet formation from progenitor cells located throughout the adult pancreas and β-cell replication occurring within existing islets. The present review sets forth to more clearly distinguish the differences between the postnatal pathways of islet neogenesis and β-cell replication with a discussion of the potential implications for reversal of Type 1 and 2 diabetic patients using islet neogenesis agents that are now in development. For Type 1 diabetic patients, an immune tolerance agent in conjunction with an islet neogenesis agent may allow achievement of adequate islet mass, perhaps with subsequent potential to withdraw medications. For Type 2 diabetic patients, lifestyle changes and/or medications may sustain the production of new islets and limit the accelerated β-cell apoptosis characteristic of the condition.

Problems and practical solutions in the external quality control of point of care devices with respect to the measurement of blood glucose

Point of care testing (POCT) is evolving at an ever increasing rate. This article deals mainly with the aspect of POCT for blood glucose and the problems of external quality assessment (EQA) of point of care devices (POCD). At the present time it is only possible to control precision with EQA, independent of the matrix of the test materials (synthetic polymer-base, plasma/serum, or processed whole blood). The German Federal Medical Council guidelines for laboratory performance allow an interlaboratory imprecision of +/-16%. The majority of POCD fulfill these requirements. The long-term stability of results--tested by repeated distribution of the same materials over a 12-month period--is excellent, and the performance of POCD under routine condtions is usually excellent in terms of result-comparability. The problems of accuracy in terms of control materials have still to be mastered.

The relationship of fasting serum radioimmune insulin levels to incident coronary heart disease in an insulin-treated diabetic cohort

It is not known whether insulin levels, in the setting of insulin treatment, are an independent risk factor for coronary heart disease (CHD). We studied a cohort of 116 insulin-treated individuals, 65 yr or older, who were followed for 5.6-9 yr. All were free of CHD at baseline. There were 47 incident CHD events. In Cox proportional hazards modeling, with fasting immune-reactive insulin levels as a continuous variable, the hazard ratio for CHD was statistically significant (P < 0.0001). When insulin levels were divided into intervals, those in the third interval [43-150 microU/ml (258-900 pmol/liter)] had an adjusted 30% increased relative risk (95% confidence interval, 0.57, 2.98) compared with those in the first interval [<20 microU/ml (<120 pmol/liter)]. Those in the fourth interval [151-400 microU/ml (906-2400 pmol/liter)] had an adjusted 5.6-fold increased risk (2.3-13.1; P < 0.0001). Approximately 15% of the cohort had such elevated insulin levels. Immune-reactive insulin levels were strongly correlated with specific insulin, proinsulin, and insulin antibody levels. Markedly elevated fasting immune-reactive insulin levels were an independent risk factor for CHD in this study of insulin-treated older adults. These observational findings should be confirmed through larger prospective studies, given their implications for insulin therapy.

Third trimester glycemic profiles and fetal growth

Diabetes is a common complication of pregnancy. Third trimester hyperglycemia has been associated in both gestational and pregestational diabetes with deviant fetal growth. Recent studies demonstrated that peak postprandial glucose levels in normal pregnancy are lower than previously thought. This finding could explain the lack of effectiveness reported by some investigators in achieving a rate of macrosomia similar to the general population. Among different possible blood glucose determinations, it appears that 1-hour postprandial as well as the overall mean blood glucose levels are the most closely correlated with fetal growth. It seems that a narrow window of glycemic levels is associated with optimal fetal growth because excessively tight glycemic control has been associated with increased incidence of small-for-gestational-age infants.

A spectrum of glucose thresholds may effectively prevent complications in the pregnant diabetic patient

This article outlines the probable positive relationship between levels of maternal glycemia and perinatal morbidity and mortality. A spectrum of different glucose thresholds can be established and used appropriately to prevent each complication. This article also outlines the concept of normality and what definitions of normality should be used to evaluate the relationship between the level of glycemia and perinatal outcome. Definitive conclusions are hampered by a lack of uniformity in definitions and interventions, and by a failure in some analyses to control for confounding variables. However, it is suggested that different levels of glycemia are required to prevent different diabetic complications. Thus, although it is not always possible to achieve targeted levels of glycemic control in all patients, any improvement will be beneficial because it will affect fetal complications associated with that glucose threshold.

Third-trimester maternal glucose levels from diurnal profiles in nondiabetic pregnancies: correlation with sonographic parameters of fetal growth

OBJECTIVE

To assess the 24-h glucose levels in a group of nondiabetic, nonobese pregnant women and to verify the presence of correlations between maternal glucose levels and sonographic parameters of fetal growth.

RESEARCH DESIGN AND METHODS

A total of 66 Caucasian nonobese pregnant women with normal glucose challenge tests (GCT) enrolled in the study; from this population, we selected 51 women who delivered term (from 37 to 42 weeks completed) live-born infants without evidence of congenital malformations. The women were requested to have three main meals and to perform daily glucose profiles fortnightly from 28-38 weeks without modifying their lifestyle or following any dietary restriction. All subjects were taught how to monitor their blood glucose by using a reflectance meter. Fetal biometry was evaluated by ultrasound scan according to standard methodology at 22, 28, 32, and 36 weeks of pregnancy.

RESULTS

The overall daily mean glucose level during the third trimester was 74.7 +/- 5.2 mg/dl. Daily mean glucose values increased between 28 (71.9 +/- 5.7 mg/dl) and 38 (78.3 +/- 5.4 mg/dl) weeks of pregnancy. We found a significant positive correlation at 28 weeks between 1-h postprandial glucose values and fetal abdominal circumference (AC). At 32 weeks, we documented positive correlations between fetal AC and maternal blood glucose levels 1 h after breakfast, 1 and 2 h after lunch, and 1 and 2 h after dinner. At 36 weeks, there was a positive correlation between fetal AC and 1- and 2-h postprandial blood glucose levels. In addition, there was a negative correlation between head-abdominal circumference ratio and 1-h postprandial blood glucose values.

CONCLUSIONS

This longitudinal study first provides a contribution toward the definition of normoglycemia in nondiabetic, nonobese pregnant women; moreover, it reveals significant correlations of postprandial blood glucose levels with the growth of insulin-sensitive fetal tissues and, in particular, between 1-h postprandial blood glucose values and fetal AC.

Level of glycemia and perinatal outcome in pregestational diabetes

This article provides the reader with relevant information regarding the association between level of glycemia and perinatal outcome in preexisting diabetes. Although the glycemic profile is a continuum in nature, different thresholds of glucose are associated with fetal complications such as stillbirth, spontaneous abortion, congenital anomalies, fetal macrosomia, and metabolic and respiratory complications. For each complication, a different targeted threshold of normality is required. Thus, although it is not always possible to achieve optimal glycemic control in all patients, any improvement will be beneficial because it will reduce the rate of complications for a given glucose threshold.

Screening and diagnosis of gestational diabetes

This chapter discusses the evidence for the existence of an entity called 'gestational diabetes', suggesting that it can be understood in terms of risk to the pregnancy and/or risk to the mother. Various diagnostic criteria used in various parts of the world are described, and a rationale for using pregnancy-specific criteria is put forth. Universal screening approaches are also characterized. Barriers to the universal adoption of a single screening scheme and set of diagnostic criteria are outlined.

Metabolism and placental transfer of 125I-proinsulin and 125I-tyrosylated C-peptide in the pregnant rhesus monkey

125I-Proinsulin or 125I-tyrosylated-C-peptide (125I-tyr-CP) was administered to pregnant Rhesus monkeys by bolus followed by constant infusion to examine placental transfer of these peptides. At the end of each infusion, fetuses were exsanguinated in situ via the umbilical vein. The bolus-constant infusion technique produced a steady state in maternal plasma of immunoprecipitable label, measured using excess insulin or C-peptide antiserum. In animals infused with 125I-proinsulin, analysis of umbilical venous plasma revealed no apparent transfer to the fetus of immunoprecipitable label. In animals infused with 125I-tyr-CP, 3-13% of the umbilical venous plasma radioactivity was immunoprecipitable, representing 1.4-5.8% of the immunoprecipitable radioactivity in maternal plasma at delivery. Gel filtration chromatography of umbilical venous plasma revealed that the immunoprecipitated moiety was a fragment of 125I-tyr-CP. Analysis of maternal plasma showed that the predominant peak of radioactivity represented intact C-peptide. A peak corresponding to the fetal immunoprecipitable peak was also present. Analysis of simultaneous maternal arterial and uterine vein plasma samples showed that degradation of 125I-tyr-CP occurred across the uterus. Studies in one nonpregnant and three postpartum animals indicated that pregnancy increased the rate of metabolism of 125I-tyr-CP. When 125I-tyr-CP was incubated with trophoblastic cells in culture, degradation to a species corresponding on gel filtration to the immunoprecipitable fetal metabolite was found. We conclude that proinsulin, like insulin, does not traverse the placenta. Immunoreactive fragments of C-peptide do cross, however, and pregnancy alters the metabolism of 125I-tyr-CP, probably owing to placental degradation.

C-peptide measurement: methods and clinical utility

Proinsulin is the single chain precursor of insulin. It consists of insulin, plus a peptide which connects the A and B chains of insulin. This peptide is termed C-peptide. C-peptide an insulin are secreted in equimolar amounts from pancreatic beta-cells, Hence, circulating C-peptide levels provide a measure of beta-cell secretory activity. C-peptide measurements are preferable to insulin measurements because of lack of hepatic extraction, slower metabolic clearance rate, and lack of cross reactivity with antibodies to insulin. This article reviews the methods for determination of C-peptide levels in body fluids, and discusses the applications of C-peptide measurement. These include the investigation of hypoglycemia and the assessment of insulin secretory function in insulin-treated and non-insulin-dependent diabetics. The contribution of C-peptide measurement to the understanding of the interrelationships between insulin secretory function and age, sex, obesity, blood lipids, and blood glucose concentrations will also be evaluated.

Free and total insulin integrated concentrations in insulin dependent diabetes

Studies of the 24 hr insulin concentration profiles in diabetic subjects on chronic exogenous insulin have been hampered by the presence of endogenous anti-insulin antibody, which gives spurious estimates of radioimmunoassayable insulin concentrations. The introduction of polyethylene glycol precipitation of endogenous antibody has allowed development of reliable assays for determination of free and total insulin concentration in subjects on insulin therapy. This article reports our observations of plasma free and total insulin concentration in 50 Type I and Type II ambulatory insulin dependent diabetics, utilizing a continuous 24 hr blood withdrawal technique. In response to exogenous insulin, study subjects had marked elevations in insulin concentrations compared to controls. Mean free insulin integrated concentration was 3.5-fold higher in diabetics than nondiabetics. Mean total insulin integrated concentration was 868 microunits/ml, more than 20 times in excess of total insulin concentration in nondiabetics. There was a wide range among diabetics in the percentage of total insulin in the free insulin fraction. Neither free nor total insulin integrated concentration correlated with dose of exogenous insulin. Free and total insulin concentration profiles showed a limited range of variation in insulin concentration during the 24 hr of study, no subject having a profile that mimicked that observed in nondiabetic subjects. Glucose integrated concentration showed no correlation with free insulin integrated concentration, however, it did correlate inversely with the percentage of total insulin in the free insulin fraction. These data emphasize the difficulty in establishing normal patterns of insulin among diabetic subjects on conventional subcutaneous insulin therapy.

Free insulin, C-peptide and glucagon profiles in insulin dependent diabetes mellitus

Glucose and hormone profiles, including plasma levels of glucagon, GH, total insulin, free immunoreactive and biologically active insulin were determined by hourly sampling in two groups of insulin dependent diabetics. The five patients in Group I were recently diagnosed and still had residual beta-cell function. The other six in Group II had disease of longer duration, had developed insulin antibodies, and were non-secretors of C-peptide. All patients were studied while receiving their usual maintenance doses of Semilente monocomponent insulin (Novo). Daily insulin requirements were 25.6 +/- 4 U in Group I and 52.2 +/- 7 U in Group II. The glucose profiles were similar in the periprandial periods but over the whole 24-hour period control was more unstable in the patients of Group II and during the period 2400-0200 h plasma glucose fell to low levels (minimum plasma glucose 1.5-3.0 mmol/l). Free insulin levels rose to peak levels over a similar time course but then fell more slowly in the Group II subjects. These patients had higher free, biologically active insulin and lower glucagon levels which were coincident in time with the early morning hypoglycaemia. These observations suggest that raised free insulin levels in the setting of an impaired counter-regulatory glucagon response are one of the factors contributing to glucose instability in long-standing diabetics.

Free insulin, bound insulin, C-peptide and the metabolic control in juvenile onset diabetics: comparison of C-peptide secretors and non-secretors during 24 hours conventional insulin therapy

In two groups of juvenile onset diabetics similar in age, weight, diet and daily insulin dosage (eight without C-peptide, group I; eight with C-peptide, group II) the serum levels of free and antibody bound insulin, C-peptide, glucose, lactate, alanine and FFA were determined over 24 h. In addition the affinity and binding capacity of the insulin antibodies were determined in vitro. No correlation was found between free or bound insulin and glucose. This holds true for the individual profiles as well as for the averaged profiles of the two groups. Free insulin and lactate or alanine were positively correlated in the C-peptide secreting group. C-peptide secretion followed the flucturations of the glucose level during 24 h in each individual patient. As a group, C-peptide secretors were better controlled than non-secretors with respect to mean blood glucose, M-value and the lability index and showed higher free insulin levels despite a similar daily insulin dosage. The possible reasons for this fact are discussed. No correlation was found between the affinity characteristics of the insulin antibodies and the degree of metabolic control or the daily insulin dosage.

Proinsulin and C-peptide in diabetes

The availability of C-peptide measurement continues to provide new and useful information about the state of beta cell secretory function and the natural history of diabetes. Measurement of proinsulin is of value in the diagnosis of insulin-secreting tumors.

Metabolism during normal and diabetic pregnancy and its effect on neonatal outcome

Diurnal profile studies have been used to define the fetal carbohydrate and lipid substrate environment in normal and diabetic women during late pregnancy. In women with normal glucose tolerance the diurnal plasma glucose concentration was maintained within close limits (mean +/- S.D., 4.70 +/- 0.38 mmol/l) but in chemical and insulin-dependent diabetics there was a marked increase in both the mean diurnal glucose value and in the variability of the plasma glucose levels observed through the day (mean +/- S.D., 5.61 +/- 5.61 +/- 1.03 and 6.02 +/- 1.26 mmol/l respectively, P less than 0.01). No difference was observed between the peripheral insulin activity of the normal and chemical diabetic women, and the impaired glucose tolerance of the latter group was due to a deficient insulin response to goucose. The diurnal glucose variability, expressed as the standard deviation of the mean, was found to be inversely correlated with the residual C-peptide response in insulin-requiring diabetics. The mean diurnal plasma free fatty acid (FFA) concentration was slightly raised in chemical diabetic subjects compared to normal women (mean +/- S.D., 0.77 +/- 0.34 and 0.68 +/- 0.20 mmol/l respectively) but this difference was not significant. Insulin treatment produced a marked reduction in circulating FFA concentration, with a mean value in the insulin-dependent diabetic group of 0.45 +/- 0.11 mmol/l (P less than 0.001). Neonatal glucose assimilation during the first two hours of life correlated strongly with several functions of maternal carbohydrate tolerance. This was associated with higher plasma insulin concentrations at birth, and a marked tendency to hypoglycaemia in the infants of untreated chemical diabetic women. Impaired mobilization of triglyceride stores was also observed during the two hours after birth in the infants of diabetic women. This, however, appears to be due not to impaired lipolysis but to rapid re-esterification of FFA. These findings all indicate a state of functional hyperinsulinism in the infant of the diabetic women secondary to maternal hyperglycaemia.