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Hypertensive Disorders in Pregnancy and Subsequent Diabetes Mellitus: A Retrospective Cohort Study

      Abstract

      Background

      Cohort study on the association between hypertensive disorders in pregnancy (HDP) and postpartum diabetes is limited. This retrospective cohort study investigated the incidence of diabetes mellitus after delivery among women with HDP using claims data of a universal insurance system.

      Methods

      We defined the HDP group as women aged 19-40 years with their first HDP in 2003, excluding those with a history of gestational diabetes mellitus, diabetes mellitus, or hypertension before the date of diagnosis with HDP. Women who had normal pregnancy without HDP were randomly chosen as our comparison group, frequency matched with age and index year of the HDP group. Both groups were followed until December 31, 2008 to evaluate the occurrence of diabetes.

      Results

      This study consisted of 1139 women with HDP cases and 4527 non-HDP pregnant women. Overall, the subsequent incidence of diabetes mellitus was 5.08-fold higher in the HDP group than in the non-HDP group, with an adjusted hazard ratio of 3.42 (95% confidence interval [CI], 2.07-5.64) after controlling for age, occupation, income, and comorbidity. The hazard ratio of developing diabetes increased to 39.5 (95% CI, 13.0-120.6) for women having HDP, hyperlipidemia, and obesity simultaneously.

      Conclusions

      Women with HDP have a high risk of subsequent diabetes. HDP women with obesity and hyperlipidemia are at an extremely high risk of diabetes mellitus. Early identification of women with HDP is needed for prevention, particularly those with other comorbidities.

      Keywords

      Gestational hypertension and preeclampsia are hypertensive disorders in pregnancy (HDP).
      • Helewa M.E.
      • Burrows R.F.
      • Smith J.
      • Williams K.
      • Brain P.
      • Rabkin S.W.
      Report of the Canadian Hypertension Society Consensus Conference: 1. Definitions, evaluation and classification of hypertensive disorders in pregnancy.
      Gestational hypertension is defined as the onset of hypertension (≥140/90 mm Hg) without proteinuria after 20 weeks of gestation, while preeclampsia is referred to as the onset of hypertension (≥140/90 mm Hg) with proteinuria (≥0.3 g/24 hours), also after 20 weeks of gestation. HDP may complicate 5%-10% of all pregnancies.
      • Saftlas A.F.
      • Olson D.R.
      • Franks A.L.
      • Atrash H.K.
      • Pokras R.
      Epidemiology of preeclampsia and eclampsia in the United States, 1979-1986.
      Gestational hypertension evolves into preeclampsia in 10%-20% of cases.
      • Saudan P.
      • Brown M.A.
      • Buddle M.L.
      • Jones M.
      Does gestational hypertension become pre-eclampsia?.
      Preeclampsia is one of the common causes of maternal and fetal morbidity and mortality.
      • Hauth J.C.
      • Ewell M.G.
      • Levine R.J.
      • et al.
      Pregnancy outcomes in healthy nulliparas who developed hypertension Calcium for Preeclampsia Prevention Study Group.
      Both case-control and cohort studies have reported that women with HDP are at an elevated risk of later metabolism disorders and cardiovascular disease.
      • Bellamy L.
      • Casas J.P.
      • Hingorani A.D.
      • Williams D.J.
      Pre-eclampsia and risk of cardiovascular disease and cancer in later life: systematic review and meta-analysis.
      • Lykke J.A.
      • Langhoff-Roos J.
      • Sibai B.M.
      • Funai E.F.
      • Triche E.W.
      • Paidas M.J.
      Hypertensive pregnancy disorders and subsequent cardiovascular morbidity and type 2 diabetes mellitus in the mother.
      • McDonald S.D.
      • Malinowski A.
      • Zhou Q.
      • Yusuf S.
      • Devereaux P.J.
      Cardiovascular sequelae of preeclampsia/eclampsia: a systematic review and meta-analyses.
      Metabolic abnormalities, including obesity, insulin resistance, and dyslipidemia, featuring metabolic syndrome, are risk factors for both HDP and cardiovascular disease.
      • Kaaja R.
      Insulin resistance syndrome in preeclampsia.
      • Parretti E.
      • Lapolla A.
      • Dalfra M.
      • et al.
      Preeclampsia in lean normotensive normotolerant pregnant women can be predicted by simple insulin sensitivity indexes.
      • Sibai B.M.
      • Gordon T.
      • Thom E.
      • et al.
      Risk factors for preeclampsia in healthy nulliparous women: a prospective multicenter study The National Institute of Child Health and Human Development Network of Maternal-Fetal Medicine Units.
      • Solomon C.G.
      • Graves S.W.
      • Greene M.F.
      • Seely E.W.
      Glucose intolerance as a predictor of hypertension in pregnancy.
      • Wolf M.
      • Sandler L.
      • Munoz K.
      • Hsu K.
      • Ecker J.L.
      • Thadhani R.
      First trimester insulin resistance and subsequent preeclampsia: a prospective study.
      On the other hand, HDP may lead to an exaggeration of insulin resistance and is associated with abnormal metabolic change during pregnancy.
      • Kaaja R.
      • Laivuori H.
      • Laakso M.
      • Tikkanen M.J.
      • Ylikorkala O.
      Evidence of a state of increased insulin resistance in preeclampsia.
      Vascular and metabolic abnormalities occurring in HDP may persist through postpartum.
      • Girouard J.
      • Giguere Y.
      • Moutquin J.M.
      • Forest J.C.
      Previous hypertensive disease of pregnancy is associated with alterations of markers of insulin resistance.
      • Laivuori H.
      • Tikkanen M.J.
      • Ylikorkala O.
      Hyperinsulinemia 17 years after preeclamptic first pregnancy.
      • Pouta A.
      • Hartikainen A.L.
      • Sovio U.
      • et al.
      Manifestations of metabolic syndrome after hypertensive pregnancy.
      Therefore, it is likely that women predisposed to insulin resistance are more likely to develop HDP and more likely to have subsequent hypertension, atherosclerosis, and type 2 diabetes mellitus in later life, which eventually lead to cardiovascular disease.
      • The postpartum incidence of diabetes mellitus is approximately 5-fold higher in women with hypertensive disorders in pregnancy (HDP) than in women without HDP.
      • Among women with HDP, those with preeclampsia/eclampsia are more likely to develop diabetes mellitus than women with only gestational hypertension.
      • The hazard ratio of developing diabetes mellitus increased to approximately 40-fold higher for women with HDP, hyperlipidemia, and obesity simultaneously.
      Limited cohort studies have reported the association between HDP and subsequent diabetes mellitus (DM) for Western populations.
      • Lykke J.A.
      • Langhoff-Roos J.
      • Sibai B.M.
      • Funai E.F.
      • Triche E.W.
      • Paidas M.J.
      Hypertensive pregnancy disorders and subsequent cardiovascular morbidity and type 2 diabetes mellitus in the mother.
      • Callaway L.K.
      • Lawlor D.A.
      • O'Callaghan M.
      • Williams G.M.
      • Najman J.M.
      • McIntyre H.D.
      Diabetes mellitus in the 21 years after a pregnancy that was complicated by hypertension: findings from a prospective cohort study.
      • Carr D.B.
      • Newton K.M.
      • Utzschneider K.M.
      • et al.
      Preeclampsia and risk of developing subsequent diabetes.
      • Libby G.
      • Murphy D.J.
      • McEwan N.F.
      • et al.
      Pre-eclampsia and the later development of type 2 diabetes in mothers and their children: an intergenerational study from the Walker cohort.
      The Danish National Patient Registry study found that preeclampsia is associated with 3.12-3.68–fold risk of developing type 2 diabetes.
      • Lykke J.A.
      • Langhoff-Roos J.
      • Sibai B.M.
      • Funai E.F.
      • Triche E.W.
      • Paidas M.J.
      Hypertensive pregnancy disorders and subsequent cardiovascular morbidity and type 2 diabetes mellitus in the mother.
      The risk of diabetes is much greater for women with preeclampsia who undergo preterm delivery and deliver infants who are small for gestational age. However, no study has investigated the interaction of pregnant hypertensive disorders with other metabolic abnormalities for the subsequent DM. This retrospective cohort study investigated the risk of DM after delivery for Asian women with HDP and interaction with other metabolism abnormalities, using population-based universal insurance claims data.

      Materials and Methods

       Data Source

      Data used in this study were extracted from National Health Insurance Research Database, an electronic claims database of the Taiwan National Health Insurance (NHI) program. Details of the NHI have been described elsewhere.
      • Lu J.F.
      • Hsiao W.C.
      Does universal health insurance make health care unaffordable? Lessons from Taiwan.
      Briefly, NHI is a universal health insurance program reformed in providing health care services to 99% of the population of Taiwan. More than 90% of health care institutions have contracted with the NHI. For this study, we used a subset of the National Health Insurance Research Database containing comprehensive health care data including files of inpatient claims, ambulatory care claims, and prescriptions for one million people randomly selected from the entire 23 million beneficiaries of NHI. We linked these files using the encrypted unique personal identifiers to obtain longitudinal medical history of each individual. Diagnoses were based on the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). The scrambled personal identifications secured the individual's confidentiality, preventing ethical violation of the claims data.

       Study Subjects

      We conducted the retrospective cohort analysis to determine the association between HDP (ICD-9 code 642) and DM (ICD-9 code 250 or A-code A181). From the 1997-2003 claims data, we identified 1520 women aged 19-40 years with their first HDP. Exclusions were those with a baseline history of gestational DM (n = 280; ICD-9 code 648.0 and 648.8), and those with DM (n = 55) or hypertension (n = 146) identified before the date of diagnosis with HDP. The remaining 1139 women with the first HDP were considered as the HDP cohort. Women who had normal pregnancy (ICD-9 code 650 or A-code A41) without HDP were randomly chosen as our comparison group, frequency matched on age (every 5 years) and the index year of HDP group, using the inclusion criteria similar to the HDP group. The HDP and non-HDP groups were selected in a 1:4 ratio in order to enhance the power of statistical tests. All subjects were followed-up to evaluate the occurrence of diabetes until December 31, 2008 or censored because of death, withdrawal from the insurance program, or loss to follow-up. Comorbidities including obesity (ICD-9 code 278.0 or A-code A183), hyperlipidemia (ICD-9 code 272 or A-code A182), preterm delivery (ICD-9 code 644), and abruption (ICD-9 code 641.2) were considered in data analyses.

       Statistical Analysis

      Data analyses first calculated the incidences of DM developed in both HDP and non-HDP groups and the HDP-to-non-HDP rate ratios by demographic status and comorbidities such as obesity, hyperlipidemia, preterm delivery, and placenta abruption. The Cox proportional hazardous regression analyses measured corresponding hazard ratios (HRs) with 95% confidence intervals (95% CIs). Both crude HRs and multivariable adjusted HRs were measured. Simple linear regression was used to evaluate trends of rate ratios for diabetes in HDP vs non-HDP groups for age, occupation, and income. Logistic regression model was used to measure odds ratios with 95% CIs to evaluate the associations between HDP and baseline comorbidities, including obesity, hyperlipidemia, and the history of preterm delivery or placenta abruption. We plotted the Kaplan-Meier curves to compare the probability of diabetes developing between women with HDP and without HDP during the study period and used the log-rank test to examine the significance of difference between the 2 groups. To differentiate how the risk of diabetes was associated with age between the HDP and non-HDP cohorts, we measured the HR for each age group, compared with non-HDP subjects aged 19-24 years. Interactions between HDP and baseline metabolism abnormalities in association with developing diabetes also were measured. Information on metabolism abnormalities in terms of obesity and hyperlipidemia is available in the claims data. For the HDP group, we further classified them into 2 groups: women with only gestational hypertension (ICD-9 code 642.3) and women with preeclampsia/eclampsia (ICD-9 codes 642.4-642.6) to examine whether the severity of the hypertensive disorder correlated with the HR of developing diabetes. We used SAS software (version 9.1 for windows; SAS Institute Inc., Cary, NC) for all statistical analyses. All significant levels were set at a 2-tailed P value of <.05. Kaplan-Meier curves were plotted using R (version 2.11.1; R Development Core Team, Vienna, Austria, 2010).

      Results

      This study consisted of 1139 women with HDP and 4527 non-HDP women for data analyses after excluding ineligible subjects. The mean ages were similar in the HDP and non-HDP groups (29±4.8 years). The mean follow-up periods were 8.1±2.1 years in the HDP cohort and 8.2±2.0 years in the non-HDP cohort (data not shown).
      Table 1 demonstrates the incidences of DM in both cohorts, HDP-to-non-HDP rate ratios, and HRs of DM by socioeconomic status and comorbidity. The incidence of diabetes was 5.08-fold greater in the HDP women than in non-HDP women (42.4 vs 8.34 per 10,000 person-years); it increased with age in both groups. The age-specific incidence of diabetes increased much more in the HDP group than in the non-HDP group (P for trend <.0001). The incidence rate ratio also increased with age, from 2.67 for women aged 19-24 years to 9.64 for those aged 35-40 years, with an HR of 4.15 (95% CI, 1.52-11.4) for the oldest women compared with the youngest women. The incidence of diabetes was 87.3 per 10,000 person-years in the oldest HDP women, nearly 10-fold greater than their counterpart non-HDP women. Among the comorbidities, the risk of developing diabetes had strong association with hyperlipidemia (adjusted HR 12.2; 95% CI, 7.47-19.9) and obesity (adjusted HR 6.61; 95% CI, 3.17-13.8) but not with preterm delivery and abruption. The Kaplan-Meier analysis shows that the cumulative incidence of diabetes was 6% greater in the HDP group than in the non-HDP group, more prominent after the 7-year follow-up (P <.001) (Figure).
      Table 1Comparisons of Diabetic Incidences Between Women With and Without Hypertensive Disorders of Pregnancy and Associated Hazard Ratios by Sociodemographic Status and Comorbidity
      VariablesNon-HDPHDPRate RatioCrude HR (95% CI)Adjusted
      Adjusted for age, occupation, and income.
      HR (95% CI)
      nCasesPYRate
      Per 10,000 person-years.
      nCasesPYRate
      Per 10,000 person-years.
      All45273137,1558.34113939920442.45.085.1(3.19-8.18)
      P <.0001.
      4.99(3.11-8.00)
      P <.0001.
      Age, years
       19-24804366864.52012166912.02.671.00(Reference)1.00(Reference)
       25-291540912,5627.23858312425.63.571.84(0.68-5.00)1.94(0.71-5.27)
       30-3415201412,38511.338017303656.04.953.35(1.30-8.62)3.52(1.36-9.13)
      P <.01.
       35-40663555229.117312137587.39.644.06(1.50-10.99)
      P <.01.
      4.15(1.52-11.35)
      P <.01.
      Occupation
       White collar29882024,1768.374518598930.13.631.00(Reference)1.00(Reference)
       Blue collar949783208.425012208157.76.851.38(0.80-2.40)1.42(0.80-2.51)
       Unemployed
      Unemployed: retired, low income.
      590446598.61449113479.49.251.81(0.96-3.39)2.14(0.97-4.70)
      Income
       <15,0001462812,1866.637818308558.38.891.00(Reference)1.00(Reference)
       15,000-29,99923611319,2356.857818462238.95.760.77(0.46-1.30)0.89(0.48-1.62)
       ≥30,00070410573417.41833149720.01.151.07(0.55-2.09)1.23(0.54-2.77)
      Co-morbidities
       Obesity
        No44722836,6847.6108634877138.85.081.00(Reference)1.00(Reference)
        Yes55347163.6535433115.41.816.33(3.03-13.2)6.61(3.17-13.8)
       Hyperlipidemia
        No41561434,0154.195913769416.94.111.00(Reference)1.00(Reference)
        Yes37117314054.1180261510172.13.1813.8(8.53-22.4)12.2(7.47-19.9)
       Preterm delivery
        No45022636,9427.0105727847131.94.531.00(Reference)1.00(Reference)
        Yes255213234.78212733163.70.702.02(0.63-6.42)1.84(0.58-5.85)
       Abruption
        No45273137,1558.3113339915042.65.111.00(Reference)1.00(Reference)
        Yes00060540.0
      CI=confidence interval; HDP=hypertensive disorders in pregnancy; HR=hazard ratio; PY=person-years.
      low asterisk Per 10,000 person-years.
      Adjusted for age, occupation, and income.
      P <.0001.
      § P <.01.
      Unemployed: retired, low income.
      Figure thumbnail gr1
      FigureThe Kaplan-Meier model measured the diabetes-free proportions in the study cohorts with and without hypertensive disorders in pregnancy (HDP) during the follow-up period.
      Table 2 shows the prevalence of selected morbidities in association with HDP in the study subjects. Patients with HDP were more prevalent with obesity (4.7% vs 1.2%, P <.001), hyperlipidemia (15.8% vs 8.2%, P <.001), and preterm delivery (7.2% vs 0.6%, P <.001).
      Table 2Odds Ratio of HDP in Association with Comorbidities in Univariate and Multivariate Logistic Regression Models
      HDP CasesModel 1Model 2
      VariablesYes/NoOR(95% CI)OR(95% CI)
      Obesity
       No1086/44721(Reference)1(Reference)
       Yes53/553.97(2.71-5.82)
      P <.001.
      3.98(2.71-5.83)
      P <.001.
      Hyperlipidemia
       No959/41561(Reference)1(Reference)
       Yes180/3712.1(1.74-2.55)
      P <.001.
      2.09(1.72-2.53)
      P <.001.
      Preterm delivery
       No1057/45021(Reference)1(Reference)
       Yes82/2514(8.88-22.0)
      P <.001.
      13.9(8.82-21.8)
      P <.001.
      Abruption
       No1133/45271(Reference)1(Reference)
       Yes6/0
      CI=confidence interval; HDP=hypertensive disorders in pregnancy; OR=odds ratio. Model 1: Unadjusted; Model 2: Adjusted for age and occupation.
      low asterisk P <.001.
      Table 3 shows the age-specific hazard of diabetic development for HDP and non-HDP groups separately, comparing with 19- to 24-year-old women in the non-HDP group, after controlling for occupation, obesity, hyperlipidemia, and abruption. Age interacted with HDP. The increase of diabetic risk in the HDP group was particularly strong for patients aged 30-34 years and above with an adjusted HR of 8.87 (95% CI, 2.46-32.0) (P for trend .0004). Overall, the HDP cohort had a higher risk of diabetes than the non-HDP cohort, with an adjusted HR of 3.42 (95% CI, 2.07-5.64) after controlling for age, occupation, income, and comorbidity.
      Table 3Age-specific Incidence of Diabetes in Women With and Without HDP and Cox Proportional Hazard Regression Measured Age-specific Hazard Ratio Compared With 19-24 Years Group in Non-HDP Group
      Non-HDPHDP
      VariablesDMPYIncidence
      Per 10,000 person-years.
      HR(95% CI)DMPYIncidence
      Per 10,000 person-years.
      HR(95% CI)
      All
      Adjusted for age, occupation, obesity, and hyperlipidemia.
      3137,1558.341(Reference)39920442.43.42(2.07-5.64)
      Age, years
      Adjusted for occupation, obesity, and hyperlipidemia.
       19-24366864.491.00(Reference)2166912.02.24(0.37-13.43)
       25-29912,5627.161.57(0.42-5.81)8312425.63.43(0.90-13.09)
       30-341412,38511.32.12(0.61-7.40)17303656.07.00(2.02-24.26)
       35-40555229.051.49(0.36-6.27)12137587.38.87(2.46-31.98)
      P for trend.15.0004
      CI=confidence interval; DM=diabetes mellitus; HDP=hypertensive disorders in pregnancy; HR=hazard ratio; PY=person-years.
      low asterisk Per 10,000 person-years.
      Adjusted for age, occupation, obesity, and hyperlipidemia.
      Adjusted for occupation, obesity, and hyperlipidemia.
      The HDP women were further stratified into 2 subgroups by the severity of hypertensive disorders. Women with preeclampsia/eclampsia had a higher risk of developing diabetes (adjusted HR 4.15; 95% CI, 2.48-6.95) (Table 4), while women with only gestational hypertension were less likely to develop diabetes (adjusted HR 1.73; 95% CI, 0.78-3.81).
      Table 4Multivariable Cox Proportional Hazard Regression Analysis for Risk of Diabetes in Women With and Without Hypertensive Disorders in Pregnancy
      GroupnDMPYIncidence
      Per 10,000 person-years.
      HR(95% CI)
      Non-HDP45273137,1558.341.00(Reference)
      GHT only4888386420.701.73(0.78-3.81)
      Preeclampsia/eclampsia65131534058.054.15(2.48-6.95)
      P <.001.
      CI=confidence interval; DM=diabetes mellitus; GHT=gestational hypertension; HDP=hypertensive disorders in pregnancy; HR=hazard ratio; PY=person-years. Adjusted for age, occupation, obesity, hyperlipidemia.
      low asterisk Per 10,000 person-years.
      P <.001.
      Data analyses further observed whether comorbidity interacted with HDP in the subsequent development of DM. The incidences of DM associated with HDP and preterm delivery or placenta abruption were not large enough to observe the effect. However, hyperlipidemia interacted strongly with HDP and obesity. The HR of developing diabetes increased to 39.5 (95% CI, 13.0-120.6) for women with HDP, hyperlipidemia, and obesity simultaneously (Table 5).
      Table 5Interaction between HDP and Preterm Delivery Associated with Diabetes in Cox Regression Analysis Controlling for Sociodemographic Factors and Other Comorbidities
      VariablesModel 1Model 2
      HDPObesityHyperlipidemianDMPYIncidence
      Per 1,000 person-years.
      HR(95% CI)HR(95% CI)
      NoNoNo41801434,2400.411(Reference)1(Reference)
      NoYesNo4003410.00
      NoNoYes3541429924.6811.2(5.31-23.4)10.1(4.78-21.2)
      NoYesYes17314820.246.4(13.3-161.5)40.9(11.7-142.6)
      YesNoNo946127951.583.90(1.81-8.44)3.94(1.82-8.51)
      YesYesNo2712214.5211.0(1.44-83.3)12.6(1.66-96.3)
      YesNoYes15522130616.839.5(20.2-77.3)33.0(16.7-65.1)
      YesYesYes27421818.344.9(14.8-136.3)39.5(13.0-120.6)
      CI=confidence interval; DM=diabetes mellitus; HDP=hypertensive disorders in pregnancy; HR=hazard ratio; PY=person-years. Model 1: Unadjusted; Model 2: Adjusted for age, occupation.
      low asterisk Per 1,000 person-years.

      Discussion

      To the best of our knowledge, this study is the first one observing a high risk of subsequent DM associated with HDP for Asian women. The pathogenesis of preeclampsia is likely related to both maternal and fetal/placental factors.
      • Granger J.P.
      • Alexander B.T.
      • Bennett W.A.
      • Khalil R.A.
      Pathophysiology of pregnancy-induced hypertension.
      • Levine R.J.
      • Maynard S.E.
      • Qian C.
      • et al.
      Circulating angiogenic factors and the risk of preeclampsia.
      • Roberts J.M.
      • Cooper D.W.
      Pathogenesis and genetics of pre-eclampsia.
      It is likely that preeclampsia develops when abnormal placentation, through the release of anti-angiogenic factors, interacts with maternal constitutional metabolic syndrome.
      • Ness R.B.
      • Sibai B.M.
      Shared and disparate components of the pathophysiologies of fetal growth restriction and preeclampsia.
      Gestational hypertension may share the same pathophysiological effect as preeclampsia.
      Several cohort studies have demonstrated that insulin resistance in early pregnancy predisposes to HDP.
      • Parretti E.
      • Lapolla A.
      • Dalfra M.
      • et al.
      Preeclampsia in lean normotensive normotolerant pregnant women can be predicted by simple insulin sensitivity indexes.
      • Solomon C.G.
      • Graves S.W.
      • Greene M.F.
      • Seely E.W.
      Glucose intolerance as a predictor of hypertension in pregnancy.
      • Wolf M.
      • Sandler L.
      • Munoz K.
      • Hsu K.
      • Ecker J.L.
      • Thadhani R.
      First trimester insulin resistance and subsequent preeclampsia: a prospective study.
      Cross-sectional studies also have shown that HDP is associated with increased insulin resistance and metabolic syndrome in the third trimester (relative to normal pregnancy).
      • Kaaja R.
      • Laivuori H.
      • Laakso M.
      • Tikkanen M.J.
      • Ylikorkala O.
      Evidence of a state of increased insulin resistance in preeclampsia.
      • Dane B.
      • Dane C.
      • Kiray M.
      • Koldas M.
      • Cetin A.
      A new metabolic scoring system for analyzing the risk of hypertensive disorders of pregnancy.
      Insulin resistance and associated metabolic syndrome may still persist after delivery.
      • Girouard J.
      • Giguere Y.
      • Moutquin J.M.
      • Forest J.C.
      Previous hypertensive disease of pregnancy is associated with alterations of markers of insulin resistance.
      • Laivuori H.
      • Tikkanen M.J.
      • Ylikorkala O.
      Hyperinsulinemia 17 years after preeclamptic first pregnancy.
      • Pouta A.
      • Hartikainen A.L.
      • Sovio U.
      • et al.
      Manifestations of metabolic syndrome after hypertensive pregnancy.
      These studies have clearly indicated an important relationship of potentially predisposing insulin resistance to HDP. Moreover, insulin resistance is exaggerated in HDP and persists after delivery in women with a history of HDP. In our study, obesity and hyperlipidemia, components of metabolic syndrome, interact strongly with HDP for developing DM.
      Several other recent studies also have demonstrated that HDP is associated with developing subsequent DM.
      • Lykke J.A.
      • Langhoff-Roos J.
      • Sibai B.M.
      • Funai E.F.
      • Triche E.W.
      • Paidas M.J.
      Hypertensive pregnancy disorders and subsequent cardiovascular morbidity and type 2 diabetes mellitus in the mother.
      • Callaway L.K.
      • Lawlor D.A.
      • O'Callaghan M.
      • Williams G.M.
      • Najman J.M.
      • McIntyre H.D.
      Diabetes mellitus in the 21 years after a pregnancy that was complicated by hypertension: findings from a prospective cohort study.
      • Carr D.B.
      • Newton K.M.
      • Utzschneider K.M.
      • et al.
      Preeclampsia and risk of developing subsequent diabetes.
      • Libby G.
      • Murphy D.J.
      • McEwan N.F.
      • et al.
      Pre-eclampsia and the later development of type 2 diabetes in mothers and their children: an intergenerational study from the Walker cohort.
      A cohort study by Libby et al
      • Libby G.
      • Murphy D.J.
      • McEwan N.F.
      • et al.
      Pre-eclampsia and the later development of type 2 diabetes in mothers and their children: an intergenerational study from the Walker cohort.
      found that mothers with preeclampsia had an adjusted odds ratio of 1.40 (95% CI, 1.12-1.75) for developing type 2 DM. But they did not exclude women with preexisting or gestational diabetes for their study. Callaway et al
      • Callaway L.K.
      • Lawlor D.A.
      • O'Callaghan M.
      • Williams G.M.
      • Najman J.M.
      • McIntyre H.D.
      Diabetes mellitus in the 21 years after a pregnancy that was complicated by hypertension: findings from a prospective cohort study.
      performed a survey and found that HDP was associated with subsequent diabetes 21 years after the pregnancy, with an adjusted odds ratio of 1.76 (95% CI, 1.21-2.56). However, that study also did not exclude women with gestational diabetes. Carr et al
      • Carr D.B.
      • Newton K.M.
      • Utzschneider K.M.
      • et al.
      Preeclampsia and risk of developing subsequent diabetes.
      reported that preeclampsia was associated with a high risk of subsequent diabetes, with an HR of 1.86 (95% CI, 1.22-2.84).
      • Carr D.B.
      • Newton K.M.
      • Utzschneider K.M.
      • et al.
      Preeclampsia and risk of developing subsequent diabetes.
      But their study did not adjust for confounding variables such as obesity and lifestyle. A Denmark registry-based study showed that the HRs of subsequent type 2 DM were 3.12 (95% CI, 2.63-3.70) for women with gestational hypertension and 3.63 (95% CI, 3.34-3.93) for women with preeclampsia. For women with preterm delivery and preeclampsia, the HR increased to 6.59 (95% CI, 5.34-8.13).
      • Lykke J.A.
      • Langhoff-Roos J.
      • Sibai B.M.
      • Funai E.F.
      • Triche E.W.
      • Paidas M.J.
      Hypertensive pregnancy disorders and subsequent cardiovascular morbidity and type 2 diabetes mellitus in the mother.
      They also found that women with 2 episodes of preeclampsia had increased risk of subsequent type 2 diabetes, compared with women with only 1 episode of preeclampsia. But this study also failed to exclude gestational diabetes and adjust for the confounding effect of obesity and hyperlipidemia.
      In our study, we excluded women with preexisting hypertension, diabetes, or gestational diabetes at the baseline to reduce the confounding effect of gestational diabetes and preexisting hypertension. HDP was associated with subsequent diabetes with an HR of 3.42 after controlling for age, occupation, and comorbidities. The risk is significantly increased with maternal age, and much stronger than in women without HDP. Among women with HDP, those with preeclampsia/eclampsia have more severe hypertensive disorders. Most diabetes cases developed subsequently were in women who had experienced preeclampsia/eclampsia.
      Another important finding in this study is that the women simultaneously having HDP, hyperlipidemia, and obesity are at extremely high risk of subsequent development of DM. This interaction term has not been reported previously. However, the interaction between preterm delivery and HDP was not significant in this study (P=.99; data not shown). Because there was only 1 woman who had HDP twice (data not shown), we also failed to observe a significant trend in the development of diabetes associated with multiple HDP episodes.

       Limitations

      Our study has several limitations. First, the National Health Insurance Research Database provided limited information on sociodemographic characteristics, with information unavailable on marital status, educational level, smoking habit, and laboratory data. These variables could not be adjusted in the analysis. However, controlling for smoking habit and parity resulted in only a small change in odds ratio according to a previous study.
      • Callaway L.K.
      • Lawlor D.A.
      • O'Callaghan M.
      • Williams G.M.
      • Najman J.M.
      • McIntyre H.D.
      Diabetes mellitus in the 21 years after a pregnancy that was complicated by hypertension: findings from a prospective cohort study.
      Moreover, we were able to use occupation and income for adjustment. Second, some information on chronic conditions, such as hyperlipidemia and obesity, was unavailable for a few individuals. However, this situation happened in both groups. Finally, prenatal care may be different between medical centers, regional hospitals, local hospitals, and obstetrician clinics. The prenatal care at clinics has been standardized to adhere to the insurance system. Insurance claims are subject to be reviewed and validated by auditors of medical records to insure the accuracy of the claims. It is not likely that the prenatal care diagnosis of HDP will vary. Most women receive their prenatal care at hospitals. Our further data analysis showed that women in the HDP group and the non-HDP group had made 140 and 120 clinic visits on average, respectively, during the study period. Examination for DM was likely included in the routine clinic check-up.

      Conclusions

      In conclusion, our study results can be generalized to pregnant women in Taiwan for the association between HDP and diabetes risk because we used a representative pregnant population data. The risk of subsequent diabetes in women with HDP was 3.4 times more than in those with uncomplicated pregnancy. The risk doesn't increase further for women with both HDP and preterm delivery, but increases drastically for women with HDP and comorbidities of hyperlipidemia and obesity. Moreover, older pregnant women with HDP may have a much higher risk of subsequent diabetes than younger pregnant women with HDP. Close surveillance for diabetes should be considered for women with HDP, particularly for those with a history of preeclampsia/eclampsia. Lifestyle or pharmacological interventions also should be considered for these high-risk women.

      Acknowledgment

      This study used insurance claims data obtained from Taiwan National Health Research Institute.

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