Characterization of the insulin-like growth factor axis in term pregnancies complicated by maternal obesity

The Long-Term Effect of Maternal Obesity on the Cardiovascular Health of the Offspring-Systematic Review

Maternal obesity may affect offspring's cardiovascular health. Our literature search using PubMed, Web of Sciences included original English research and Google Scholar articles published over the past ten years, culminating in 96 articles in this topic. A mother's obesity during pregnancy has a negative impact on the cardiovascular risk for their offspring. Dependence was observed in relation to hypertension, coronary artery disease, stroke, and heart failure. The adverse impact of an abnormal diet in pregnant mice on heart hypertrophy was observed, and was also confirmed in human research. Pregnant women with obesity were at greater risk of having a child with innate heart disease than pregnant women with normal mass. To conclude: mother's obesity has a negative impact on the long-term cardiovascular consequences for their offspring, increasing their risk of high blood pressure, coronary heart disease, stroke and heart failure. It also increases the probability of heart hypertrophy and innate heart defects.

Hormonal Determinants of Growth and Weight Gain in the Human Fetus and Preterm Infant

The factors controlling linear growth and weight gain in the human fetus and newborn infant are poorly understood. We review here the changes in linear growth, weight gain, lean body mass, and fat mass during mid- and late gestation and the early postnatal period in the context of changes in the secretion and action of maternal, placental, fetal, and neonatal hormones, growth factors, and adipocytokines. We assess the effects of hormonal determinants on placental nutrient delivery and the impact of preterm delivery on hormone expression and postnatal growth and metabolic function. We then discuss the effects of various maternal disorders and nutritional and pharmacologic interventions on fetal and perinatal hormone and growth factor production, growth, and fat deposition and consider important unresolved questions in the field.

Role of Hormones During Gestation and Early Development: Pathways Involved in Developmental Programming

Accumulating evidence suggests that an altered maternal milieu and environmental insults during the intrauterine and perinatal periods of life affect the developing organism, leading to detrimental long-term outcomes and often to adult pathologies through programming effects. Hormones, together with growth factors, play critical roles in the regulation of maternal-fetal and maternal-neonate interfaces, and alterations in any of them may lead to programming effects on the developing organism. In this chapter, we will review the role of sex steroids, thyroid hormones, and insulin-like growth factors, as crucial factors involved in physiological processes during pregnancy and lactation, and their role in developmental programming effects during fetal and early neonatal life. Also, we will consider epidemiological evidence and data from animal models of altered maternal hormonal environments and focus on the role of different tissues in the establishment of maternal and fetus/infant interaction. Finally, we will identify unresolved questions and discuss potential future research directions.

Maternal obesity and acute lymphoblastic leukemia risk in offspring: A summary of trends, epidemiological evidence, and possible biological mechanisms

Acute lymphoblastic leukemia, a heterogenous malignancy characterized by uncontrolled proliferation of lymphoid progenitors and generally initiated in utero, is the most common pediatric cancer. Although incidence of ALL has been steadily increasing in recent decades, no clear reason for this trend has been identified. Rising concurrently with ALL incidence, increasing maternal obesity rates may be partially contributing to increasing ALL prevelance. Epidemiological studies, including a recent meta-analysis, have found an association between maternal obesity and leukemogenesis in offspring, although mechanisms underlying this association remain unknown. Therefore, the purpose of this review is to propose possible mechanisms connecting maternal obesity to ALL risk in offspring, including changes to fetal/neonatal epigenetics, altered insulin-like growth factor profiles and insulin resistance, modified adipokine production and secretion, changes to immune cell populations, and impacts on birthweight and childhood obesity/adiposity. We describe how each proposed mechanism is biologically plausible due to their connection with maternal obesity, presence in neonatal and/or fetal tissue, observation in pediatric ALL patients at diagnosis, and association with leukemogenesis, A description of ALL and maternal obesity trends, a summary of epidemiological evidence, a discussion of the pathway from intrauterine environment to subsequent malignancy, and propositions for future directions are also presented.

Prenatal psychological or metabolic stress increases the risk for psychiatric disorders: the "funnel effect" model

Adverse stressful experiences in utero can redirect fetal brain development, ultimately leading to increased risk for psychiatric disorders. Obesity during pregnancy can have similar effects as maternal stress, affecting mental health in the offspring. In order to explain how similar outcomes may originate from different prenatal conditions, we propose a "funnel effect" model whereby maternal psychological or metabolic stress triggers the same evolutionarily conserved response pathways, increasing vulnerability for psychopathology. In this context, the placenta, which is the main mother-fetus interface, appears to facilitate such convergence, re-directing "stress" signals to the fetus. Characterizing converging pathways activated by different adverse environmental conditions is fundamental to assess the emergence of risk signatures of major psychiatric disorders, which might enable preventive measures in risk populations, and open up new diagnostics, and potentially therapeutic approaches for disease prevention and health promotion already during pregnancy.

Prenatal factors associated with fetal visceral adiposity

OBJECTIVE

To assess fetal visceral adiposity and associated factors during pregnancy.

METHODS

Secondary analysis of prospective cohort data with 172 pairs (pregnant woman/fetus) treated at public health units. Anthropometric data, metabolic (glucose, glycated hemoglobin, insulin, insulin resistance, total cholesterol and fractions, triglycerides) measures, fetal biometry, and visceral and subcutaneous adiposity in the binomial (pregnant woman/fetus) were evaluated at the 16^th, 28^th and 36^th gestational weeks by ultrasonography. Pearson's correlation coefficient and multiple linear regression were used, with a significance level of 5%.

RESULTS

At the 16^th week, the mean age of the pregnant women was 26.6±5.8 years and mean weight was 62.7±11.5kg; 47.0% had normal weight, 28.3% were overweight, 13.3% were underweight, and 11.2% were obese. At 36 weeks, 44.1% had inadequate gestational weight gain, 32.5% had adequate gestational weight gain, and 23.3% had excessive gestational weight gain. Fetal visceral adiposity at week 36 showed a positive correlation with maternal variables: weight (r=0.15) and body mass index (r=0.21) at the 16^th; with weight (r=0.19), body mass index (r=0.24), and gestational weight gain (r=0.21) at the 28^th; and with weight (r=0.22), body mass index (r=0.26), and gestational weight gain (r=0.21) at the 36^th week. After multiple linear regression, adiposity at the 28^th week remained associated with fetal variables: abdominal circumference (p<0.0001), head circumference (p=0.01), area (p<0.0001), and thigh circumference (p<0.001). At the 36^th week, adiposity remained associated with the abdominal circumference of the 28^th (p=0.02) and 36^th weeks (p<0.001).

CONCLUSION

Adiposity was positively correlated with the measurements of the pregnant woman. After the multivariate analysis, the persistence of the association occurred with the abdominal circumference, a central adiposity measurement with a higher metabolic risk.

Placental proteases PAPP-A and PAPP-A2, the binding proteins they cleave (IGFBP-4 and -5), and IGF-I and IGF-II: Levels in umbilical cord blood and associations with birth weight and length

BACKGROUND

A newborn's birth weight for gestational age provides important insights into his or her fetal growth and well-being. While the underlying mechanisms regulating fetal growth remain to be fully elucidated, the IGF axis plays an important role. Some components of this axis have been well-characterized in umbilical cord blood, but others have not yet been studied. We measured the proteases PAPP-A and PAPP-A2, the binding proteins they cleave (IGFBP-4 and -5), and the established molecules IGF-I and -II in umbilical cord blood to better characterize the IGF axis in relation to birth weight and length.

METHODS

We performed a case-control study of 180 neonates born at a tertiary teaching hospital in Boston. To maximize power, infants were recruited in a 1:3:1 ratio with 37 SGA, 111 AGA, and 37 LGA infants matched by gestational age, sex, and delivery mode. IGF-I, IGF-II, IGFBP-4, IGFBP-5, PAPP-A, and PAPP-A2 were measured in umbilical cord blood by ELISA. Associations between birth weight and birth length Z-scores and the Z-scores of the above molecules were analyzed using linear regression models and analysis of covariance.

RESULTS

Birth weight and length Z-scores were positively associated with Z-scores of IGF-I, IGF-II, total IGFBP-4, and IGFBP-5, with IGF-I having the strongest association. Birth weight and length Z-scores were negatively associated with Z-scores of intact IGFBP-4, PAPP-A, and PAPP-A2 levels.

CONCLUSIONS

We confirm previous findings of significant associations between the IGFs in cord blood and newborn size and for the first time show positive associations between cord blood total IGFBP-4 and -5 and birth weight and a negative association between intact IGFBP-4 and birth weight. We also show for the first time a reciprocal relationship between cord blood levels of PAPP-A and PAPP-A2 and newborn size. The implications of these findings need to be further examined in large longitudinal studies and likely have diagnostic and therapeutic potential.

Impact of pregravid obesity on maternal and fetal immunity: Fertile grounds for reprogramming

Maternal pregravid obesity results in several adverse health outcomes during pregnancy, including increased risk of gestational diabetes, preeclampsia, placental abruption, and complications at delivery. Additionally, pregravid obesity and in utero exposure to high fat diet have been shown to have detrimental effects on fetal programming, predisposing the offspring to adverse cardiometabolic, endocrine, and neurodevelopmental outcomes. More recently, a deeper appreciation for the modulation of offspring immunity and infectious disease-related outcomes by maternal pregravid obesity has emerged. This review will describe currently available animal models for studying the impact of maternal pregravid obesity on fetal immunity and review the data from clinical and animal model studies. We also examine the burden of pregravid obesity on the maternal-fetal interface and the link between placental and systemic inflammation. Finally, we discuss future studies needed to identify key mechanistic underpinnings that link maternal inflammatory changes and fetal cellular reprogramming events.

The effect of maternal obesity on fetal biometry, body composition, and growth velocity

Introduction: The aim of this secondary analysis was to investigate the relationship between maternal body mass index (BMI) and fetal biometry, body composition, and velocity measurements at 28 and 36 weeks gestation.Materials and methods: The current analysis involves 911 overweight or obese women who were randomized to the Standard Care group of the LIMIT randomized trial.Results: The fetus of women with Class 3 obesity (BMI ≥ 40.0) showed the greatest increase in all biometry z-scores, abdominal area (AA), and abdominal fat mass (AFM) compared with women classified as overweight (BMI 25.0-29.9). In women with Class 3 obesity, AA velocity was increased by 0.035 cm² (0.004, 0.066, p = .029) and the z-score velocity was increased by 0.238 (0.022, 0.453, p = .03). Estimated fetal weight (EFW) velocity for women with Class 3 obesity was higher than that of overweight women by 2.028 g per day (0.861, 3.196, p<.001) and the z-score velocity was also higher by 0.441 per day (0.196, 0.687, p < .001).Conclusions: Maternal obesity is associated with an increase in fetal abdominal circumference, AFM and area along with EFW velocity over time. Women with Class 3 obesity (BMI ≥ 40.0) may represent a higher risk group for perpetuating the intergenerational transmission of obesity to their offspring.

The Influence of Maternal Obesity and Breastfeeding on Infant Appetite- and Growth-Related Hormone Concentrations: The SKOT Cohort Studies

BACKGROUND/AIMS

Exposure to obesity during pregnancy may lead to adverse changes in the offspring's metabolic profile. We compared appetite- and growth-related hormones in a cohort of infants born to obese mothers (SKOT-II) with infants born mainly to nonobese mothers (SKOT-I).

METHODS

Infants from SKOT-I (n = 273) and SKOT-II (n = 132) were examined including anthropometric measurements and blood samples analyzed for glucose, insulin, insulin-like growth factor-I (IGF-I), adiponectin, and leptin. Information on breastfeeding and parental characteristics were also collected.

RESULTS

At 9 months of age, SKOT-II infants were 3.6% heavier and 1.2% longer than SKOT-I infants even though their mothers were shorter. There was no difference in body mass index (BMI). SKOT-II infants had higher levels of insulin, adiponectin, and leptin but lower levels of IGF-I compared to SKOT-I infants (all p ≤ 0.015). These differences remained, except for leptin, when adjusted for current weight. Breastfeeding versus nonbreastfeeding at 9 months was associated with lower concentrations of all hormones (all p ≤ 0.003). In adjusted models, maternal BMI at 9 months was positively associated with insulin and adiponectin and negatively with IGF-I.

CONCLUSIONS

Pre-pregnancy obesity confers symmetrically larger infant body size and higher levels of most growth- and appetite-related hormones but surprisingly lower levels of IGF-I, suggesting other possible infant growth-promoting effects through insulin.

Human relaxins (RLNH1, RLNH2), their receptor (RXFP1) and fetoplacental growth

Relaxin, a systemic and placental hormone, has potential roles in fetoplacental growth. Human placenta expresses two RLN genes, RLNH1 and RLNH2 Maternal obesity is common and is associated with abnormal fetal growth. Our aims were to relate systemic and cord blood RLNH2, placental RLNs and their receptor (RXFP1) with fetoplacental growth in context of maternal body mass index, and associations with insulin-like growth factor 2 (IGF2) and vascular endothelial growth factor A (VEGFA) in the same placentas. Systemic, cord blood and placental samples were collected prior to term labor, divided by prepregnancy body mass index: underweight/normal (N = 25) and overweight/obese (N = 44). Blood RLNH2 was measured by ELISA; placental RLNH2, RLNH1, RXFP1, IGF2 and VEGFA were measured by quantitative immunohistochemistry and mRNAs were measured by quantitative reverse transcription PCR. Birthweight increased with systemic RLNH2 only in underweight/normal women (P = 0.036). Syncytiotrophoblast RLNH2 was increased in overweight/obese patients (P = 0.017) and was associated with placental weight in all subjects (P = 0.038). RLNH1 had no associations with birthweight or placental weight, but was associated with increased trophoblast and endothelial IGF2 and VEGFA, due to female fetal sex. Thus, while systemic RLNH2 may be involved in birthweight regulation in underweight/normal women, placental RLNH2 in all subjects may be involved in placental weight. A strong association of trophoblast IGF2 with birthweight and placental weight in overweight/obese women suggests its importance. However, an association of only RLNH1 with placental IGF2 and VEGFA was dependent upon female fetal sex. These results suggest that both systemic and placental RLNs may be associated with fetoplacental growth.

Maternal obesity and inflammatory mediators: A controversial association

The link between maternal obesity and inflammatory mediators is still unclear. Our aim was to summarize the main findings of recently published studies on this topic. We performed a search in Medline for studies published in the last years on obesity, human pregnancy, and inflammatory mediators. We report the findings of 30 studies. The characteristics and number of participants, study design, gestational age at sample collection, and type of sample varied widely. Approximately two-thirds of them investigated more than one mediator, and 50% included participants in only one trimester of pregnancy. The most frequently investigated mediators were leptin, tumour necrosis factor-alpha (TNF-α), and interleukin (IL)-6. Almost all studies reported an association between maternal obesity, leptin, and C-reactive protein (CRP) serum levels but not with IL-1β and IL-10. The association of IL-6, TNF-α, monocyte chemo-attractant protein-1 (MCP-1), adiponectin, and resistin with maternal obesity is still controversial. To clarify the physiopathological link between maternal obesity and inflammation, more high-quality studies are needed.

Implications of maternal obesity on fetal growth and the role of ultrasound

Over fifty percent of women entering pregnancy are overweight or obese. This has a significant impact on short and long term maternal and infant health outcomes, and the intergenerational effects of obesity are now a major public health problem globally. Areas covered: There are two major pathways contributing to fetal growth. Glucose and insulin directly affect growth, while other substrates such as leptin, adiponectin and insulin-like growth factors indirectly influence growth through structural and morphological effects on the placenta, uteroplacental blood flow, and regulation of placental transporters. Advances in ultrasonography over the past decade have led to interest in the prediction of the fetus at risk of overgrowth and adiposity utilizing both standard ultrasound biometry and fetal body composition measurements. However, to date there is no consensus regarding the definition of fetal overgrowth, its reporting, and clinical management. Expert commentary: Maternal dietary intervention targeting the antenatal period appear to be too late to sufficiently affect fetal growth. The peri-conceptual period and early pregnancy are being evaluated to determine if the intergenerational effects of maternal obesity can be altered to improve newborn, infant and child health.

Is Mid-trimester Insulin Resistance Predictive of Subsequent Puerperal Infection? A Secondary Analysis of Randomized Trial Data

Objective The objective of this study was to examine whether there is an association between insulin resistance and subsequent development of puerperal infection by measuring insulin resistance in the mid-trimester using the homeostasis model assessment (HOMA:IR). Methods Secondary analysis of low-risk nulliparas enrolled in a multicenter preeclampsia prevention trial. HOMA:IR was measured on fasting plasma glucose and insulin concentrations among low-risk nulliparas between 22 and 26 weeks' gestation. Median HOMA:IR was compared between women who did and did not develop puerperal infection using Wilcoxon rank sum test. Logistic regression was used to control for potential confounders. Results Of 1,180 women with fasting glucose and insulin available, 121 (10.3%) had a puerperal infection. Median HOMA:IR was higher among those with subsequent puerperal infection (4.3 [interquartile, IQR: 2.2-20.5] vs. 2.6 [IQR: 1.5-6.7], p < 0.0001). After controlling for potentially confounding variables HOMA:IR was only marginally associated with an increased risk of development of puerperal infection, adjusted odds ratio: 1.01 (95% confidence interval: 1.00-1.02; p = 0.04) per unit increase. Elevated HOMA:IR performed poorly as a predictor of puerperal infection, with a positive predictive value of 15% and a negative predictive value of 92%. Conclusion Though associated with an increased risk of puerperal infection, insulin resistance, measured by HOMA:IR, is not a clinically useful predictor of puerperal infection.

Maternal obesity affects fetal myocardial function as early as in the first trimester

OBJECTIVE

To investigate cardiac function from 14 weeks' gestation in fetuses of obese pregnant women (FOW). Animal studies have shown that maternal obesity induces fibrosis in fetal myocardium. We hypothesized that fetal cardiac function would be impaired among FOW.

METHODS

A case-control study with longitudinal follow-up was performed at Trondheim University Hospital, Norway. In total, 80 pregnant women were included and the final population comprised 52 obese and 24 of normal weight (mean body mass index before pregnancy, 34.8 ± 4.1 vs 21.0 ± 2.2 kg/m(2) ; P < 0.001). The main outcome measures were global strain rate (GSR) and strain by tissue Doppler imaging, tissue Doppler velocities (TDVs) and interventricular septal thickness assessed by fetal echocardiography at gestational ages of 14, 20 and 32 weeks.

RESULTS

In FOW, fetal left ventricle (LV) and right ventricle (RV) GSR and strain were significantly lower than in fetuses of normal-weight pregnant women: LV GSR was 33.3% lower at 14 weeks, 22.4% lower at 20 weeks and 22.8% lower at 32 weeks of gestation (P < 0.001) with no difference in fetal heart rate. Systolic and late diastolic TDVs for LV were significantly lower from 20 weeks' gestation and remained lower throughout pregnancy. Fetal interventricular septum was 26.6% (P < 0.001) thicker in late pregnancy in FOW compared with normal-weight pregnancies.

CONCLUSIONS

At 14 weeks of gestation, we detected fetal myocardial dysfunction with reduced LV and RV GSR and strain in FOW compared with fetuses of women with normal weight. Our finding is alarming considering the high prevalence of obesity and may partly explain the predisposition of offspring to cardiovascular disease later in life.

Insulin-like growth factor-binding protein 1 and 7 concentrations are lower in obese pregnant women, women with gestational diabetes and their fetuses

OBJECTIVE

To determine the effect of pre-existing maternal obesity and gestational diabetes mellitus (GDM) on the circulating levels of insulin growth factor-binding protein (IGFBPs) in cord and maternal plasma.

STUDY DESIGN

IGFBP-1-7 levels were measured on maternal and cord plasma from women with normal glucose tolerance (NGT) (30 non-obese and 36 obese) and GDM (44 non-obese and 26 obese) at the time of term elective cesarean section.

RESULT

Maternal plasma IGFBP-1, IGFBP-6 and IGFBP-rP1 concentrations were significantly lower in NGT obese compared with NGT non-obese women and in non-obese GDM women compared with non-obese NGT women. In cord plasma, IGFBP-1-3 and IGFBP-rP1 concentrations were significantly lower in NGT obese compared with NGT non-obese women and in non-obese GDM women compared with non-obese NGT women. Significant positive correlations were observed between maternal and cord plasma IGFBP-1 and IGFBP-rP1 levels and maternal insulin resistance. In cord plasma, significant positive correlations were observed between IGFBP-1-3 and IGFBP-rP1 levels and fetal insulin resistance. Fetal birthweight was inversely correlated with maternal plasma IGFBP-1 levels and cord plasma IGFBP-1 and IGFBP-2 levels. When corrected for maternal body mass index, the only significant relationship that still existed was between cord plasma IGFBP-1 concentrations and fetal birthweight.

CONCLUSION

At the time of term cesarean section, pre-existing maternal obesity and GDM are associated with lower IGFBP levels in maternal and cord plasma. Alterations in circulating IGF and IGFBPs may alter birthweight and/or neonatal adiposity. This may lead to alterations in optimal growth trajectory and lead to metabolic disorders later in life.

Effect of maternal obesity with and without gestational diabetes on offspring subcutaneous and preperitoneal adipose tissue development from birth up to year-1

Background

Maternal obesity and gestational diabetes mellitus (GDM) may independently influence offspring fat mass and metabolic disease susceptibility. In this pilot study, body composition and fat distribution in offspring from obese women with and without GDM and lean women were assessed within the 1st year of life, and maternal and newborn plasma factors were related to offspring adipose tissue distribution.

Methods

Serum and plasma samples from pregnant obese women with (n = 16) or without (n = 13) GDM and normoglycemic lean women (n = 15) at 3rd trimester and offspring cord plasma were used for analyzing lipid profiles, insulin and adipokine levels. At week-1 and 6, month-4 and year-1, offspring anthropometrics and skinfold thickness (SFT) were measured and abdominal subcutaneous (SCA) and preperitoneal adipose tissue (PPA) were determined by ultrasonography.

Results

Cord insulin was significantly increased in the GDM group, whereas levels of cord leptin, total and high molecular weight (HMW) adiponectin were similar between the groups. Neonates of the GDM group showed significantly higher SFT and fat mass until week-6 and significantly increased SCA at week-1 compared to the lean group that persisted as strong trend at week-6. Interestingly, PPA in neonates of the GDM group was significantly elevated at week-1 compared to both the lean and obese group. At month-4 and year-1, significant differences in adipose tissue growth between the groups were not observed. Multiple linear regression analyses revealed that cord insulin levels are independently related to neonatal PPA that showed significant relation to PPA development at year-1. Maternal fasted C-peptide and HMW adiponectin levels at 3rd trimester emerged to be determinants for PPA at week-1.

Conclusion

Maternal pregravid obesity combined with GDM leads to newborn hyperinsulinemia and increased offspring fat mass until week-6, whereas pregravid obesity without GDM does not. This strongly suggests the pivotal role of GDM in the adverse offspring outcome. Maternal C-peptide and HMW adiponectin levels in pregnancy emerge to be predictive for elevated PPA in newborns and might be indicative for the obesity risk at later life. Altogether, the findings from our pilot study warrant evaluation in long-term studies.

Trial registration

German Clinical Trials Register DRKS00004370

Excessive gestational weight gain and obesity contribute to altered expression of maternal insulin-like growth factor binding protein-3

BACKGROUND

Excessive gestational weight gain (GWG) increases risk of large for gestational age neonates and subsequent tracking of excess weight throughout the life course for both mother and child. Although the physiological mechanisms underlying these associations are incomplete, the insulin-like growth factor (IGF) axis has garnered attention for its role in fetal growth and development. Our purpose was to characterize the IGF axis protein expression patterns in mother-infant dyads in respect of excessive GWG.

METHODS

WE OBTAINED FASTING SERUM SAMPLES AND CORRESPONDING CORD BLOOD FROM EIGHT CONTROLS (ADHERE GROUP: ie, those who gained in accordance with 2009 Institute of Medicine GWG recommendations) and 13 exceeders (EXCEED group: ie, those who exceeded Institute of Medicine GWG recommendations). At study completion, we examined protein expression of IGF-I, IGF-II, IGF binding protein (IGFBP)-1, IGFBP-3, IGFBP-4, and hormone concentrations in both maternal and cord blood.

RESULTS

Between-group comparisons were made and revealed elevated maternal leptin (P ≤ 0.05) concentrations in gravidas who exceeded recommendations. There was a significantly higher number of obese women in the EXCEED group (P < 0.05). After adjustment, maternal leptin levels were positively correlated with maternal homeostasis model of assessment for insulin resistance score and excessive GWG (P ≤ 0.01). However, serum IGFBP-3 expression in the EXCEED mothers was greater than that in the ADHERE group (P ≤ 0.05).

CONCLUSION

These findings provide preliminary evidence suggesting that small deviations in IGFBP-regulated IGF bioavailability arising from excessive GWG/positive energy balance may affect adipocyte differentiation through subclinical insulin resistance.