Abstract
Context: Inflammatory mediators are associated with type 2 and gestational diabetes. It is unknown whether there are associations with glucose in pregnant women with lesser degrees of hyperglycemia.
Objective: The objective of the study was to examine associations of inflammatory mediators with maternal glucose levels and neonatal size in a subset of participants in the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Study.
Design: Eligible pregnant women underwent a 75-g oral glucose tolerance test between 24 and 32 wk gestation, and levels of C-peptide, adiponectin, plasminogen activator inhibitor type 1 (PAI-1), C-reactive protein (CRP), and resistin were measured in fasting serum samples. Associations of inflammatory mediators with maternal glucose and with birth size were assessed using multiple linear regression analyses, adjusting for maternal body mass index (BMI), fasting C-peptide, and other potential confounders.
Results: Mean levels of adiponectin declined, and PAI-1 and CRP increased across increasing levels of maternal glucose, BMI, and C-peptide. For example, for fasting plasma glucose less than 75 mg/dl and fasting plasma glucose of 90 mg/dl or greater, adiponectin was 22.5 and 17.4 μg/ml and PAI-1 was 30.9 and 34.2 ng/ml, respectively. Associations with 1- and 2-h plasma glucose remained significant for adiponectin (P < 0.001), PAI-1 (P < 0.05), and CRP (P < 0.01) after adjustment for BMI and C-peptide. Adiponectin and CRP were inversely associated with birth weight, sum of skinfolds and percent body fat, and PAI-1 with sum of skinfolds (all P < 0.05) after adjustment for confounders. Resistin was not associated with 1- or 2-h glucose or birth size.
Conclusion: Levels of inflammatory mediators are associated with levels of maternal glucose in pregnant women without overt diabetes.
Levels of inflammatory mediators are associated with levels of maternal glucose in pregnant women without overt diabetes.
The observation that adipose tissue produces pro- and antiinflammatory mediators (adipocytokines) suggests a potential role for chronic inflammation in the pathogenesis of type 2 diabetes mellitus (T2DM) and a possible mechanism linking obesity and insulin resistance (1). Pregnancy is characterized by insulin resistance, which leads to abnormal glucose tolerance in some women. Recent evidence suggests that inflammation also contributes to pregnancy-induced insulin resistance and the development of glucose intolerance (2).
Compared with normal pregnancy, gestational diabetes mellitus (GDM) is characterized by increased insulin resistance. Consistent with this observation, inflammatory mediators are associated with risk of developing GDM independent of obesity (3,4,5,6). For example, two studies have shown that the level of adiponectin, an antiinflammatory adipokine, is significantly lower in women with GDM compared with controls, after adjustment for body mass index (BMI) (4,6). Nondiabetic women with prior GDM have significantly higher levels of the inflammatory mediators C-reactive protein (CRP) and plasminogen activator inhibitor type 1 (PAI-1) and significantly lower levels of adiponectin, independent of BMI (7).
To date, most studies have compared the risk of GDM between women with the highest and lowest levels of an inflammatory mediator (5,8), whereas studies of the relationship between glucose levels and/or insulin resistance and plasma inflammatory mediator levels during pregnancy in women without GDM have typically been small and inconclusive. The goal of the present analysis was to determine associations of selected inflammatory mediators with glucose tolerance during pregnancy (below the level diagnostic of diabetes mellitus) and to determine whether associations are independent of maternal BMI and hyperinsulinemia, as measured by fasting C-peptide. Because the relationship of maternal circulating levels of inflammatory mediators with size at birth, independent of their effect on glucose and insulin levels, has not been examined, a secondary goal of this study was to determine associations of inflammatory mediators with size and adiposity in the offspring. To accomplish these goals, we studied a subset of women who participated in the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Study. HAPO sought to clarify the risk of adverse outcome associated with degrees of glucose intolerance during pregnancy less severe than overt diabetes mellitus (9,10).
Materials and Methods
The HAPO Study was conducted at field centers located in North America, Europe, the Middle East, Asia, and Australia. The protocol was approved by the institutional review board at all 15 field centers. All participants gave written informed consent. An external Data Monitoring Committee provided oversight. Study methods have been published (9,10,11). A brief overview is presented here.
Participants
All pregnant women at each field center were eligible to participate unless they had one or more exclusion criteria (10): age less than 18 yr, plan to deliver at another hospital, date of last menstrual period not certain and no ultrasound estimation from 6 to 24 wk of gestational age available, inability to complete the oral glucose tolerance test (OGTT) by 32 wk gestation, multiple pregnancy, conception using gonadotropin ovulation induction or by in vitro fertilization, glucose testing before recruitment or a diagnosis of diabetes during this pregnancy, diabetes antedating pregnancy requiring treatment with medication, participation in another study that might have interfered with HAPO, known conditions of HIV positivity or hepatitis B or C, prior participation in HAPO, or inability to converse in the languages used in field center forms without the aid of an interpreter. If glucose measurements were made outside HAPO after initial enrollment, the participant was excluded from further participation.
Gestational age and expected date of delivery (EDD) were determined from the date of the last menstrual period if the participant was certain of her dates. If uncertain, the EDD was determined from an ultrasound (US) performed between 6 and 24 wk gestation. Final EDD was also determined from US if: 1) gestational dating from LMP differed from US dating by more than 5 d when the US was performed between 6 and 13 weeks or 2) if dating differed by more than 10 d when the US was done between 14 and 24 wk.
For the purposes of this analysis, a subset of women of predominantly northwestern European origin (from Toronto, Canada; Belfast, United Kingdom; and Brisbane and Newcastle, Australia) and their neonates with complete data were studied. All of the neonates were born at term (37–43 wk).
Oral glucose tolerance test
Participants underwent a standard 75-g OGTT between 24 and 32 wk gestation (as close to 28 wk as possible). Plasma glucose samples were collected at fasting and 1 and 2 h after the glucose load.
Height, weight, and blood pressure were measured at the OGTT visit using standardized procedures and calibrated equipment. Data concerning smoking and alcohol use, first-degree family history of diabetes, and demographic data were collected using standardized questionnaires. Race/ethnicity was self-identified by participants.
A sample for random plasma glucose (RPG) was collected at 34–37 wk gestation as a safety measure to identify cases with hyperglycemia above a predefined threshold.
Glucose analysis and unblinding
Aliquots of fasting and 2-h OGTT and RPG samples were analyzed at field center laboratories, and values were unblinded if the fasting plasma glucose (FPG) exceeded 105 mg/dl, 2-h OGTT plasma glucose (PG) exceeded 200 mg/dl, RPG was 160 mg/dl or greater, or any PG value was less than 45 mg/dl. Otherwise, participants, caregivers, and HAPO Study staff (except for laboratory personnel) remained blinded to glucose values. To avoid the confounding effects of center-to-center analytical variation, aliquots of all OGTT specimens were analyzed at the HAPO Central Laboratory and these results are used here. A Vitros 750 analyzer (Ortho-Clinical Diagnostics, Rochester, NY) was used for glucose analysis (11). The technical error for the glucose measurement was 2.0%.
Maternal BMI
Maternal height and weight, used to calculate BMI, were obtained at the OGTT visit. Height was measured twice to the nearest 0.5 cm with a stadiometer or wall-mounted measuring tape with shoes removed and the participant’s head facing forward in the horizontal plane. If the results differed by more than 1.0 cm, measurements were repeated. Weight was measured twice to the nearest 0.1 kg on a calibrated scale with outer garments and shoes removed and repeated if the results differed by more than 0.5 kg.
Fasting C-peptide
A serum sample for fasting C-peptide was collected at the OGTT visit. Because hemolysis increases insulin degradation but does not affect C-peptide level (12) and because C-peptide and insulin are secreted in equimolar amounts, C-peptide rather than insulin was measured. C-peptide measurements were performed on an Autodelfia instrument (PerkinElmer, Boston, MA). The functional sensitivity of the assay was 0.02 ng/ml with intra- and interassay coefficients of variation of 3.2–5.0 and 1.9–3.0%, respectively, in samples with high and low C-peptide concentrations (11).
Inflammatory mediator assays
Adiponectin, PAI-1, and resistin were measured in a stored fasting serum sample obtained at the OGTT. The samples were stored at −80 C until assayed. They were measured simultaneously using a particle-based flow cytometric immunoassay (Millipore Corp., St. Louis, MO) designed for the Luminex xMAP platform (Luminex Corp., Austin, TX). Analyte concentrations were calculated from best-fit standard curves generated from calibrators for each analyte, included with each assay, according to the manufacturer’s instructions. For adiponectin, the interassay coefficient of variation (CV; sd/mean) for low and high controls included with each assay was 11.3 and 15.1%, respectively. Interassay CVs for low and high PAI-1 controls were 15.0 and 7.7%, respectively. The average interplate CV for resistin was 5.7%. The high-sensitivity CRP assay was performed on an aliquot of the same serum sample at the HAPO Central Laboratory in Belfast, UK. CRP was measured with a particle-enhanced turbidimetric immunoassay (Quantex CRP-US kit; Biokit, Barcelona, Spain) on the ILab 600 (Instrumentation Laboratories Ltd., Lexington, MA), an automated clinical chemistry analyzer.
Prenatal care and delivery
Prenatal care and timing of delivery were determined by standard field center practice. No field center arbitrarily delivered patients before full term or routinely performed cesarean delivery at a specified maternal or gestational age.
Neonatal anthropometrics
Neonatal anthropometrics were obtained within 72 h of delivery. To ensure accuracy and reliability of anthropometric data and consistency across field centers, a rigorous training and certification procedure was established for study research nurses and midwives. Personnel were trained during regional training sessions run by Clinical and Data Coordinating Center staff. A training videotape providing instruction in anthropometric measurements was viewed. Research personnel observed measurements and then performed measurements on five infants. After training and before recruitment, research personnel continued to perform measurements locally on two infants per week and demonstrated their proficiency with measuring neonatal anthropometrics during a dry-run site visit. To maintain quality control of skinfold measures, all research personnel underwent annual recertification that included reviewing the videotape and providing data in tandem with another certified individual on three to five babies.
Anthropometric measurements included weight, length, and skinfold thickness at three sites (flank, subscapular, triceps). Two measurements were made and if results differed by more than a prespecified amount (>10 g for weight, 0.5 cm for length, or 0.5 mm for skinfolds, respectively), a third was done. For these analyses, the average of the two measurements was used unless a third measurement was taken. In that case, if two of three measurements differed by less than the prespecified amount, the average of those two was used; otherwise, the average of all three was used.
Birth weight was obtained without diaper using a calibrated electronic scale. Length was measured on a standardized plastic length board constructed for use in the HAPO Study. Skinfold thickness was measured with Harpenden skinfold calipers (Baty, UK). Flank skinfold was measured on the left side just above the iliac crest on a diagonal fold on the mid axillary line, triceps by taking the vertical fold over the triceps muscle half the distance between the acromion process and olecranon, and subscapular just below the lower angle of the scapula at about a 45° angle to the spine. Mean CVs for anthropometric measurements were 0.04% for birth weight, 0.17% for length, 2.91% for flank skinfold, 2.57% for subscapular skinfold, and 2.73% for triceps skinfold. Fat mass at birth (grams) was derived using the following formula (13):
 |
where BW is birth weight in grams, FLS is the flank skinfold thickness in millimeters, and BL is birth length in centimeters. From this, percent body fat was derived as 100 × fat mass/birth weight.
Statistical analyses
Descriptive statistics include means and sds for continuous variables and numbers and percentages for categorical variables. Mean levels of inflammatory mediators were examined in categories of fasting and 1-, and 2-h PG, as well as for categories of BMI and fasting C-peptide. The categories selected are those that have been reported in previous publications (10,14), except that due to small numbers in higher categories, the top three categories were combined. Linear regression analysis was used to examine associations of inflammatory mediators with maternal fasting, 1- and 2-h PG, and neonatal birth weight; sum of skinfolds; and percent body fat. For maternal glucose, three models were run. Model I was unadjusted, model II was adjusted for maternal BMI, and model III was adjusted for maternal BMI and fasting C-peptide. For newborn size, two models were run. Model I was unadjusted and model II was adjusted for neonatal gender, gestational age at delivery, maternal BMI, fasting plasma glucose, and fasting C-peptide. Due to skewed distributions of the inflammatory mediators, log transformations of these variables were used in the linear regression analyses. All analyses were conducted in SAS (version 9.1; SAS Institute, Cary, NC).
Results
Characteristics of the 1481 blinded participants in this ancillary study are shown in Table 1 including mean and sd values for fasting serum adiponectin, PAI-1, CRP, and resistin.
Table 1.
Characteristics of HAPO inflammatory mediator study participants
| n | Mean | sd | |
|---|---|---|---|
| Maternal characteristics | |||
| Age (yr) | 1481 | 31.3 | 5.2 |
| BMI | 1481 | 28.4 | 4.8 |
| Mean arterial pressure (mm Hg)a | 1481 | 83.7 | 7.7 |
| FPG (mg/dl)a | 1481 | 82.0 | 6.6 |
| 1-h PG (mg/dl)a | 1481 | 131.5 | 29.1 |
| 2-h PG (mg/dl)a | 1481 | 109.0 | 21.4 |
| Fasting serum C-peptide (μg/ml)a | 1474 | 2.0 | 0.8 |
| Fasting serum adiponectin (μg/ml)a | 1477 | 20.4 | 12.5 |
| Fasting serum PAI-1 (ng/ml)a | 1476 | 32.6 | 12.1 |
| Fasting serum CRP (mg/liter)a | 1475 | 5.0 | 5.8 |
| Fasting serum resistin (ng/ml)a | 1473 | 26.6 | 16.2 |
| Gestational age (wk)a | 1481 | 28.5 | 1.4 |
| Newborn characteristics | |||
| Gestational age (wk) | 1481 | 39.99 | 1.2 |
| Birth weight (g) | 1481 | 3561.8 | 514.4 |
| Length (cm) | 1481 | 50.6 | 2.3 |
| Flank skinfold (mm) | 1481 | 4.3 | 1.0 |
| Triceps skinfold (mm) | 1481 | 4.1 | 0.9 |
| Subscapular skinfold (mm) | 1481 | 4.6 | 1.0 |
| Sum of skinfolds (mm) | 1481 | 13.0 | 2.7 |
| Body fat (%) | 1481 | 11.9 | 3.6 |
| Gender, male | 748 |
Measured at the OGTT.
In unadjusted analyses, the mean level of adiponectin declined with increasing glucose (Table 2), for example, from 22.5 μg/ml for FPG less than 75 mg/dl (4.2 mmol/liter) to 17.4 μg/ml for FPG 90 mg/dl or greater (5.0 mmol/liter). Mean PAI-1 and CRP increased across increasing levels of fasting and 1-, and 2-h PG. Mean PAI-1 ranged from 30.9 to 34.2 ng/ml across the lowest to the highest category of FPG. Similar ranges were found for 1- and 2-h PG. Mean CRP ranged from 4.4 to 6.8 mg/liter across the lowest to the highest category of FPG and similar increases were found for 1- and 2-hour PG. Mean resistin did not vary across glucose categories.
Table 2.
Mean (sd) inflammatory mediator level and categories of maternal glucose
| Fasting glucose
|
1-h glucose
|
2-h glucose
|
|||
|---|---|---|---|---|---|
| Glucose (mg/dl) | Mean (sd) | Glucose (mg/dl) | Mean (sd) | Glucose (mg/dl) | Mean (sd) |
| Adiponectin (μg/ml) | |||||
| <75 | 22.5 (9.9) | ≤105 | 22.1 (9.2) | ≤90 | 22.4 (9.7) |
| 75–79 | 20.8 (9.3) | 106–132 | 21.1 (11.1) | 91–108 | 21.2 (14.4) |
| 80–84 | 20.4 (10.8) | 133–155 | 19.7 (14.2) | 109–125 | 20.1 (14.4) |
| 85–89 | 20.4 (22.2) | 156–171 | 17.9 (8.4) | 126–139 | 18.1 (8.6) |
| ≥90 | 17.4 (8.5) | ≥194 | 18.9 (20.2) | ≥140 | 16.9 (8.2) |
| P trend < 0.001 | P trend < 0.001 | P trend < 0.001 | |||
| PAI-1 (ng/ml) | |||||
| <75 | 30.9 (10.7) | ≤105 | 31.2 (11.9) | ≤90 | 30.6 (10.4) |
| 75–79 | 32.0 (11.5) | 106–132 | 31.7 (10.8) | 91–108 | 32.0 (12.1) |
| 80–84 | 32.6 (12.0) | 133–155 | 33.6 (12.8) | 109–125 | 33.1 (11.7) |
| 85–89 | 33.8 (12.0) | 156–171 | 34.4 (13.8) | 126–139 | 33.9 (13.0) |
| ≥90 | 34.2 (12.3) | ≥194 | 34.1 (12.2) | ≥140 | 36.3 (13.8) |
| P trend < 0.001 | P trend < 0.001 | P trend < 0.001 | |||
| CRP (mg/liter) | |||||
| < 75 | 4.4 (6.2) | ≤105 | 3.8 (4.5) | ≤90 | 4.0 (5.3) |
| 75–79 | 4.5 (5.2) | 106–132 | 4.8 (5.6) | 91–108 | 4.5 (4.6) |
| 80–84 | 4.4 (4.5) | 133–155 | 5.4 (6.4) | 109–125 | 5.5 (6.4) |
| 85–89 | 5.6 (5.3) | 156–171 | 5.8 (6.5) | 126–139 | 5.6 (6.6) |
| ≥90 | 6.8 (8.4) | ≥194 | 5.6 (5.7) | ≥140 | 6.2 (7.4) |
| P trend < 0.001 | P trend < 0.001 | P trend < 0.001 | |||
| Resistin (ng/ml) | |||||
| < 75 | 25.7 (14.6) | ≤105 | 26.2 (16.5) | ≤90 | 26.3 (14.9) |
| 75–79 | 26.4 (15.1) | 106–132 | 27.2 (15.2) | 91–108 | 27.0 (15.3) |
| 80–84 | 27.4 (17.2) | 133–155 | 26.0 (16.9) | 109–125 | 26.6 (16.9) |
| 85–89 | 26.8 (15.5) | 156–171 | 26.5 (16.4) | 126–139 | 27.3 (19.6) |
| ≥90 | 26.0 (18.0) | ≥194 | 26.8 (16.5) | ≥140 | 24.5 (14.2) |
| P trend = NS | P trend = NS | P trend = NS | |||
NS, Not significant.
The mean level of adiponectin decreased with increasing level of maternal BMI from 23.5 in the lowest BMI category (≤23.2 kg/m2) to 16.4 μg/ml in the highest category (≥33.7 kg/m2) as shown in Table 3. Similar results were found across increasing levels of fasting C-peptide. Mean levels of PAI-1 and CRP increased with increasing levels of BMI and fasting C-peptide. The mean level of resistin was highest in the highest category of BMI and C-peptide.
Table 3.
Mean inflammatory mediator level and categories of maternal BMI and fasting C-peptide
| n | % | Adiponectin mean (sd) (μg/ml) | PAI-1 mean (sd) (ng/ml) | CRP mean (sd) (mg/liter) | Resistin mean (sd) (ng/ml) | |
|---|---|---|---|---|---|---|
| BMI (kg/m2) | ||||||
| ≤23.2 | 149 | 10.0 | 23.5 (9.9) | 32.2 (10.9) | 2.9 (3.5) | 25.4 (14.5) |
| 23.3–26.7 | 469 | 31.3 | 22.2 (13.4) | 30.9 (11.0) | 3.6 (4.2) | 26.1 (15.7) |
| 26.8–30.5 | 466 | 31.1 | 19.7 (12.9) | 32.5 (11.9) | 4.6 (5.2) | 27.1 (14.9) |
| 30.6–33.6 | 214 | 14.3 | 19.0 (13.3) | 34.2 (13.6) | 5.8 (4.5) | 25.4 (15.7) |
| ≥33.7 | 200 | 13.4 | 16.4 (7.9) | 35.6 (13.2) | 9.9 (9.5) | 29.1 (21.2) |
| P trend < 0.001 | P trend < 0.001 | P trend < 0.001 | P trend < 0.05 | |||
| Fasting C-peptide (μg/ml) | ||||||
| ≤1.2 | 235 | 15.7 | 25.2 (10.8) | 31.4 (11.3) | 4.0 (5.2) | 25.7 (15.0) |
| 1.3–1.7 | 466 | 31.1 | 22.5 (14.7) | 31.3 (11.4) | 4.1 (4.4) | 25.5 (14.8) |
| 1.8–2.3 | 418 | 27.9 | 19.5 (12.8) | 32.7 (11.1) | 4.8 (5.8) | 27.4 (17.7) |
| 2.4–2.8 | 177 | 11.8 | 16.6 (7.9) | 33.9 (14.2) | 5.9 (6.4) | 25.9 (13.6) |
| ≥2.9 | 202 | 13.5 | 14.8 (7.1) | 35.8 (13.6) | 7.7 (7.7) | 29.0 (19.0) |
| P trend < 0.001 | P trend < 0.001 | P trend < 0.001 | P trend < 0.05 | |||
n, Number in the category; %, proportion in the category.
Table 4 shows the coefficient and se for the associations of each of the inflammatory mediators with fasting and 1- and 2-h PG unadjusted and then with adjustment for maternal BMI alone and with adjustment for both BMI and C-peptide. In each of the models for adiponectin, PAI-1, and CRP, there was attenuation with adjustment for BMI and additional attenuation with adjustment for C-peptide. For adiponectin higher by 10%, mean 1- and 2-h PG were lower by 0.70 and 0.62 mg/dl, respectively. And, for PAI-1 higher by 10%, mean 1- and 2-h PGs were higher by 0.37 and 0.35 mg/dl, respectively. Similar results were found for CRP. For resistin, the only statistically significant association was in the fully adjusted model for FPG.
Table 4.
Multiple linear regression analysis of Ln-adjusted inflammatory mediators and maternal glucose: unadjusted, adjusted for BMI, and adjusted for maternal BMI and fasting C-peptide
| Model | Fasting glucose coefficient (se) | 1-h glucose coefficient (se) | 2-h glucose coefficient (se) |
|---|---|---|---|
| Adiponectin (μg/ml) | |||
| I | −2.95 (0.30)a | −12.73 (1.73)a | −9.98 (1.26)a |
| II | −1.73 (0.39)a | −9.81 (1.77)a | −8.09 (1.30)a |
| III | −0.09 (0.37) | −7.02 (1.84)a | −6.19 (1.35)a |
| PAI-1 (ng/ml) | |||
| I | 1.42 (0.44)a | 5.86 (1.94)a | 5.05 (1.42)a |
| II | 0.89 (0.42)b | 4.46 (1.91)a | 4.10 (1.40)c |
| III | 0.39 (0.38) | 3.66 (1.89)b | 3.52 (1.39)b |
| CRP (mg/liter) | |||
| I | 1.73 (0.27)a | 7.18 (1.18)a | 5.09 (0.86)a |
| II | 0.17 (0.29) | 3.67 (1.31)c | 2.80 (0.96)c |
| III | 0.00 (0.26) | 3.33 (1.30)c | 2.59 (0.96)c |
| Resistin (ng/ml) | |||
| I | −0.35 (0.27) | −0.50 (1.17) | −0.91 (0.86) |
| II | −0.45 (0.25) | −0.78 (1.15) | −1.10 (0.84) |
| III | −0.51 (0.23)b | −0.83 (1.13) | −1.16 (0.83) |
Model I, Unadjusted; model II, adjusted for maternal BMI; model III, adjusted for maternal BMI and fasting C-peptide.
P ≤ 0.001.
P < 0.05.
P ≤ 0.01.
Associations between inflammatory mediators and birth weight, sum of skinfolds, and percent body fat unadjusted, and with adjustment for gestational age at delivery, maternal BMI, fasting PG, and fasting C-peptide are shown in Table 5. Adiponectin had a significant inverse association with each of the newborn measures in the unadjusted model, and this was somewhat attenuated after adjustment for confounders, but the association remained significant. A 10% higher adiponectin was associated with birth weight lower by 7.4 g. PAI-1 had a significant inverse association with sum of skinfolds in the adjusted model, whereas CRP had a significant inverse association with all three measures of newborn size but only after adjustment for confounders. Resistin was not significantly associated with birth weight or neonatal adiposity.
Table 5.
Associations between Ln-adjusted inflammatory mediators and birth weight and adiposity
| Measure
|
Model
|
Adiponectin (μg/ml)
|
PAI-1 (ng/ml)
|
CRP (mg/liter)
|
Resistin (ng/ml)
|
||||
|---|---|---|---|---|---|---|---|---|---|
| Coefficient | P value | Coefficient | P value | Coefficient | P value | Coefficient | P value | ||
| Birth weight | I | −144.47 | <0.001 | −5.23 | 0.878 | 22.14 | 0.293 | −5.22 | 0.801 |
| II | −74.29 | 0.013 | −43.37 | 0.158 | −66.65 | 0.002 | 7.87 | 0.670 | |
| Sum of skinfolds | I | −0.76 | <0.001 | −0.25 | 0.156 | 0.11 | 0.302 | 0.13 | 0.226 |
| II | −0.33 | 0.045 | −0.42 | 0.013 | −0.26 | 0.024 | 0.14 | 0.169 | |
| Percent body fat | I | −1.04 | <0.001 | 0.01 | 0.964 | 0.11 | 0.464 | −0.05 | 0.729 |
| II | −0.50 | 0.027 | −0.26 | 0.272 | −0.51 | 0.002 | −0.01 | 0.934 | |
Model I, Unadjusted; model II, adjusted for neonatal gender, gestational age at delivery, maternal BMI, fasting plasma glucose, and fasting C-peptide.
A total of 213 of the pregnant women included in this study (15%) met the newly recommended criteria for GDM (15). When they were removed from the analyses, the pattern of findings, in general, remained the same (data not shown).
Discussion
Pregnancy is characterized by insulin resistance, which appears to be due, in part, to circulating levels of inflammatory mediators (2). The placenta produces a variety of inflammatory mediators, including PAI-1, resistin and possibly adiponectin (16,17). Although CRP is produced largely by the liver, the degree to which other circulating inflammatory mediators in pregnant women originate from the placenta compared with other tissues is unclear (16). Interestingly, women with GDM have increased levels of circulating inflammatory mediators, and placental overexpression of genes encoding inflammatory mediators in a diabetic environment has been demonstrated (2,16). The mechanism for the increased production is unclear, but we have now demonstrated that the association of inflammatory mediators with glycemia during pregnancy spans the full range of glucose below that diagnostic of diabetes. In our large observational study of pregnant women without overt diabetes, we have demonstrated that adiponectin was inversely and CRP and PAI-1 were positively associated with maternal fasting, 1- and 2-h PG, insulin as measured by C-peptide, and BMI. The significant associations with 1- and 2-h PG were independent of BMI and C-peptide. New associations of these molecules with size at birth were also demonstrated. In contrast, although resistin was highest in the highest categories of BMI and C-peptide, after full adjustment for confounders, it was significantly associated only with fasting plasma glucose and was not associated with any measures of size at birth.
Adiponectin is an antiinflammatory adipokine produced primarily by adipocytes, and low plasma levels of adiponectin are associated with insulin resistance in obesity and T2DM (18,19,20). Adiponectin levels are also reduced in women who have had GDM (7,21) and are lower in women with GDM during late pregnancy compared with nondiabetic pregnant controls matched for BMI (6,22,23). In addition, lower levels of adiponectin early in pregnancy are predictive of development of GDM later in pregnancy (24). In the present study, adiponectin was negatively associated with maternal glucose, C-peptide, and BMI across the full range of maternal glucose. In addition, adiponectin levels were negatively associated with birth weight, sum of skinfolds, and percent body fat before and after adjustment for potential confounders including maternal BMI and fasting glucose and C-peptide. A previous study in nonpregnant and normal pregnant women found a significant inverse association between maternal adiponectin and birth weight and included adjustment for maternal BMI (25). However, another larger study, which included 631 non-GDM women, demonstrated no association of birth weight with adiponectin after adjustment for maternal body size, glucose, and insulin (26). A study of women with GDM and normal women found that maternal adiponectin was inversely associated with birth weight but only among those with GDM (27). The larger sample size and power of the present study allowed us to demonstrate a negative association of maternal adiponectin levels with birth weight across the full range of maternal glucose.
Circulating levels of PAI-1, a protein that is an inhibitor of fibrinolysis and is secreted by adipocytes (28), are elevated in normal pregnancy and further elevated in women with GDM (29). Among women with prior GDM, increased PAI-1 levels are associated with insulin resistance and adiposity (30). Another marker of inflammation is CRP, which is associated with incident T2DM in women independent of obesity and other known risk factors for T2DM (31). Elevated CRP has also been shown to be associated with risk of GDM independent of maternal prepregnancy adiposity (32). The association of PAI-1 and CRP levels with glucose in pregnant women without GDM has not previously been reported. We now demonstrate a positive association of CRP and PAI-1 levels with maternal fasting and 1- and 2-h PG as well as fasting C-peptide and BMI. Whether these are primary changes that contribute to pregnancy-induced insulin resistance or are changes secondary to other inflammatory factors remains to be determined.
Given the known association of maternal glycemia and BMI with size at birth (14,33), we also examined the association of maternal CRP and PAI with size at birth. We are not aware of other studies that have examined these inflammatory mediators and birth outcomes. We found a negative association between PAI-1 and sum of skinfolds. Interestingly, although CRP levels are typically increased in the setting of obesity and insulin resistance, after adjustment for gestational age at delivery, maternal BMI, fasting PG, and fasting C-peptide, we found a negative association between CRP and each measurement of newborn size. This suggests that among women who are similar with respect to neonatal gender, gestational age at delivery, BMI, FPG, and fasting C-peptide, those with a lower level of CRP, for example, will have a larger fatter baby. The mechanism for this association will require further study, but this finding is consistent with previous demonstration of a correlation between elevated maternal serum CRP levels and lower birth weight in women with preeclampsia (34).
Circulating levels of resistin, an adipocytokine thought to be a potential marker of inflammation, are increased in pregnancy (35), but findings in women with GDM compared with controls have been inconsistent with higher, lower, and no change in circulating levels of resistin reported (36,37,38). Small sample sizes may have contributed to these disparate findings. In the present study with greater power than these earlier studies, resistin levels were not associated with maternal glucose. This suggests that circulating levels of inflammatory mediators are not uniformly increased in pregnant women, rather specific mediators demonstrated an association with glucose. Resistin was not associated with any of the measures of newborn size. This finding is consistent with the results of two small studies of normal pregnant women and birth weight of their offspring (39,40).
Strengths of the HAPO Study data include availability of glucose results across a broad range, careful and standardized research measurements of maternal height and weight, newborn anthropometrics, and glucose and fasting C-peptide levels (as an index of insulin sensitivity).
Previous studies have demonstrated that lower levels of adiponectin and higher levels of PAI-1 and CRP are associated with risk of (24,32), presence of (20,32), or history of GDM (7,21). We have now demonstrated that a similar association is present across the full range of glucose levels in pregnant women without overt diabetes. This adds to the findings of the main HAPO Study, which showed continuous graded associations of glucose and primary and secondary outcomes (10) and provides support to the hypothesis that inflammatory mediators are associated with glucose across the full range during pregnancy.
Acknowledgments
Members of the HAPO Study Cooperative Research Group are listed in the Appendix of the HAPO Study Cooperative Research Group (10).
Footnotes
The HAPO Study is supported by Grants R01-HD34242 and R01-HD34243 from the Eunice Kennedy Shriver National Institute of Child Health and Human Development and the National Institute of Diabetes and Digestive, and Kidney Diseases, the National Center for Research Resources (Grants M01-RR00048 and M01-RR00080), and the American Diabetes Association. This ancillary study is funded by a Northwestern Memorial Foundation 2008 Dixon Translational Research Grant.
Disclosure Summary: The authors have nothing to disclose.
First Published Online September 15, 2010
Abbreviations: BMI, Body mass index; CRP, C-reactive protein; CV, coefficient of variation; EDD, expected date of delivery; FPG, fasting plasma glucose; GDM, gestational diabetes mellitus; HAPO, Hyperglycemia and Adverse Pregnancy Outcome; OGTT, oral glucose tolerance test; PAI-1, plasminogen activator inhibitor type 1; PG, plasma glucose; RPG, random plasma glucose; T2DM, type 2 diabetes mellitus; US, ultrasound.
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