DOI: 10.2337/diacare.29.03.06.dc05-1940 © 2006 by the American Diabetes Association
Long-Acting Injectable Progestin Contraception and Risk of Type 2 Diabetes in Latino Women With Prior Gestational Diabetes Mellitus
1 Department of Preventive Medicine, University of Southern California Keck School of Medicine, Los Angeles, California Address correspondence reprint requests to Anny H. Xiang, PhD, Keck School of Medicine, University of Southern California, Department of Preventive Medicine, 1540 Alcazar St., CHP-222, Los Angeles, CA 90033. E-mail: xiang{at}usc.edu
OBJECTIVETo investigate the impact of a long-acting injectable progestin, depo-medroxyprogesterone acetate (DMPA), compared with combination oral contraceptives (COCs) on the risk of diabetes in Latino women with prior gestational diabetes mellitus (GDM).
RESEARCH DESIGN AND METHODSAn observational cohort study of 526 Hispanic women with prior GDM who were not diabetic in their postpartum visit during January 1987 to October 1997 and who elected DMPA (n = 96) or COCs (n = 430) as initial contraception were followed for a maximum of 9.2 years with a median follow-up of RESULTSAnnual diabetes incidence rates were 19% in the DMPA group and 12% in the COC group, with an unadjusted hazard ratio (HR) of 1.58 (95% CI 1.002.50; P = 0.05) for DMPA compared with COCs. Adjustment for baseline imbalances reduced the HR to 1.18 (0.672.28; P = 0.57). Additional adjustment for weight gain during follow-up, which was on average 1.8 kg higher in the DMPA group (P < 0.0001), reduced the HR to 1.07. DMPA interacted with baseline serum triglyceride levels and, separately, with breast-feeding to increase the diabetes risk. CONCLUSIONSDMPA use was associated with an increased risk of diabetes that appeared to be explained by three factors: 1) use in women with increased baseline diabetes risk, 2) weight gain during use, and 3) use with high baseline triglycerides and/or during breast-feeding.
Abbreviations: COC, combination oral contraceptive DMPA, depo-medroxyprogesterone acetate GDM, gestational diabetes mellitus OGTT, oral glucose tolerance test
Latino women with prior gestational diabetes mellitus (GDM) have a high risk of type 2 diabetes during their reproductive years (14), which is increased by additional pregnancies (5). Conceiving with mild, asymptomatic diabetes can double the risk of birth defects in offspring (6), making safe and effective methods of contraception crucial. Among highly effective methods, sterilization (e.g., tubal ligation) and intrauterine devices are metabolically neutral, while metabolic effects of hormonal contraceptives vary according to the specific formulation and dosage (4,7,8). In a prior study, we observed in a group of predominantly Latino women with recent GDM that those who selected low-dose combination oral contraceptives (COCs) had no increased risk of diabetes compared with women who selected nonhormonal contraception (4). By contrast, women who selected progestin-only oral contraceptives while breast-feeding had a nearly threefold excess risk of diabetes that was not explained by breast-feeding per se. Injectable depo-medroxyprogesterone acetate (DMPA) is another progestin-only contraceptive that offers high effectiveness and longer duration. Relatively little has been published regarding the metabolic effect of DMPA in healthy women (9,10) and none regarding its use in women with prior GDM. The present study examines the risk of diabetes associated with DMPA use in subjects derived from the same patient population as our prior study of combination and progestin-only oral contraceptives and nonhormonal contraception (4).
In 1987, we initiated a follow-up program of glucose tolerance testing of women with prior GDM at Los Angeles County Womens and Childrens Hospitals High-Risk Family Planning Clinic. The cohorts for several publications have been derived from these patients (1,4,5), of whom 97% have Spanish surnames and were born in Mexico or Central America. Women with GDM were scheduled for a 75-g oral glucose tolerance test (OGTT) 46 weeks postpartum in combination with a standard family planning visit. Women who returned for the postpartum test were scheduled for annual OGTT testing thereafter. Women who elected to use hormonal contraception were scheduled for an additional OGTT 36 months after method initiation. Women also returned for interim visits in the event of an intercurrent medical problem, a desire to change methods, and every 6 months for COC refills or every 3 months for DMPA injections. OGTTs were not performed at interim visits, but blood pressure, weight, and systems review were obtained. At each OGTT visit, women underwent a physical examination, contraceptive counseling, and were advised to exercise daily and attain or maintain ideal body weight. When impaired glucose tolerance or abnormal lipid levels were found, subjects received additional lifestyle counseling and a nutritionist appointment. When diabetes, the study end point, or overt lipid abnormalities (e.g., total cholesterol 240, LDL cholesterol 160, HDL cholesterol 55, or triglycerides 500 mg/dl) (11) were found, subjects were referred to a medicine clinic. Data for analyses are from women who 1) did not have diabetes at the initial postpartum OGTT, 2) initiated contraception with either DMPA or COCs at the first documented postpartum visit, and 3) had at least one additional OGTT before switching to a nonstudy contraceptive or becoming pregnant. The comparator group was limited to women who selected COCs for two reasons. First, COCs did not increase the risk of diabetes compared with nonhormonal methods (4). Second, the frequency of 1st-year diabetes testing was similar in women using DMPA and COCs, eliminating potential bias in diabetes rates due to differences in testing frequency. This study was approved by University of Southern California Institutional Review Board.
Selection of contraception
Testing procedures
Data analysis
Was DMPA use associated with any risk of diabetes in women with prior GDM?
Was there any particular group of women that might be susceptible to an increased diabetes risk during DMPA use?
A total of 526 women met the subject selection criteria, 96 who initially elected DMPA and 430 who initially elected COCs. Of 430 women in the COC group, 67% received monophasic norethindrone (Ovcon) and 25% received the triphasic levonorgestrel (Triphasil). The remaining 8% all received COCs containing low-dose estrogen (<35 µg) with varying doses of norethindrone ( 1.0 mg) or levonorgestrel ( 0.150 mg). At baseline (Table 1), the DMPA and COC groups were similar with regard to the frequency of insulin treatment during the index pregnancy (prescribed for persistent fasting glycemia 105 mg/dl) and baseline age, parity, OGTT glucose, blood pressure, and total cholesterol. The DMPA group had significantly higher baseline BMI and frequency of diabetes in family members and lower HDL cholesterol and triglyceride levels. At entry, 23% of women in the DMPA group were breast-feeding.
The medians and interquartile ranges for length of follow-up were 11.3 (14.2) and 12.0 (21.3) months in the DMPA and COC groups, respectively (P = 0.44). The median months of uninterrupted use of initial contraception method were 11.2 and 12.0 months, respectively (P = 0.15). Only 11 women switched between DMPA and COCs during follow-up, 7 who started with DMPA and 4 who started with COCs. For the 22 women who were breast-feeding at baseline, the median duration of breast-feeding was 5.9 months with a range of 2.326.7 months. The DMPA group had significantly more weight gain than the COC group (2.1 ± 3.6 vs. 0.3 ± 2.8 kg; P < 0.0001).
Was DMPA use associated with any risk of diabetes in women with prior GDM?
Cox regression analysis examining DMPA use as a time-dependent variable provided an unadjusted hazard ratio (HR) of 1.58 (95% CI 1.002.50; P = 0.05) compared with COC use. Analysis assuming two separate HRs, one for the 1st year of use and one for subsequent years of use, did not provide better model fitting than the single HR model. Thus, one constant HR across follow-up time best described the risk pattern. Since DMPA users had higher baseline BMIs, rates of breast-feeding, and family members with diabetes and lower HDL cholesterol and triglyceride levels, analysis was repeated with these five baseline variables as covariates. After adjusting for these covariates, the risk associated with DMPA use decreased from 1.58 to 1.18 (95% CI 0.672.28; P = 0.57). Additional adjustment for weight gain during follow-up further reduced the risk estimate to 1.07 (0.611.89; P = 0.81).
Was there any particular group of women that might be susceptible to an increase in diabetes risk during DMPA use?
There also was an interaction between breast-feeding and DMPA (Table 2). Compared with COC use, DMPA use without breast-feeding was associated with no increase in the risk of developing diabetes, but DMPA use with breast-feeding significantly increased the risk of diabetes (unadjusted HR 3.45, adjusted HR 2.21). Even within the DMPA group, the 22 women who breast-fed had a more than twofold increase in adjusted diabetes risk compared with the 74 who did not (adjusted HR 2.21 [95% CI 0.697.02], P = 0.18), although this difference was not statistically significant.
We found that Latino women with prior GDM who, with the advice of their care providers, elected to use DMPA had an increased risk of developing diabetes compared with women who elected to use COCs. However, the increased risk appeared to be due to a combination of factors. First, baseline differences in weight, breast-feeding status, family history of diabetes, and lipids appeared to account for much of the difference in diabetes risk between DMPA and COC groups. This finding may reflect prescribing or patient selection bias at the initial selection of contraceptive method. Second, weight gain during DMPA use may have contributed in a small way to increased diabetes risk. Third, use of DMPA with relatively high baseline triglycerides or during breast-feeding increased the risk of diabetes. Our finding of increased risk associated with DMPA use in combination with breast-feeding is consistent with our previous report from the same high-risk patient group (4). In that report, we found that the progestin-only oral contraceptives (0.35 mg norethindrone), which were prescribed only during breast-feeding, were associated with a 2.9-fold increase in the risk of developing diabetes compared with using of COCs. Breastfeeding per se (i.e., without hormonal contraceptives) was not associated with an increased risk of diabetes; thus, there appears to be an interaction between breast-feeding and use of progestin-only contraceptives that increases blood glucose levels, thereby increasing the incidence of diabetes after GDM. While we have not investigated the physiological mechanism for this interaction, we speculate that exposure to progestins when endogenous estrogen levels are low (e.g., during breast-feeding) may exaggerate the imbalance between insulin resistance and insulin secretion that is already present in patients with a history of GDM. Our current findings support that speculation, not only in the direction but also in the magnitude of diabetes risk, which was approximately two- to threefold in both of our studies of progestin-only contraception. The risk in the present study was of borderline statistical significance in the adjusted analysis, most likely due to the relatively small number of women who elected DMPA and breastfeed in the present study (22 women) compared with our previous study (78 women) (4); thus, our power is limited. The interplay among triglyceride levels, contraception, and the risk of diabetes was complex. Neither DMPA use with relatively low triglycerides nor COC use with relatively high triglycerides (i.e., above the cohort median of 150 mg/dl) significantly increased the risk of diabetes compared with COC use with relatively low triglycerides. By contrast, DMPA use with relatively high triglycerides increased the risk more than twofold compared with COC use with low triglycerides. Thus, neither triglycerides nor DMPA use had an important effect to increase diabetes rates alone, but together they increased the risk, demonstrating the significant interaction between the two factors. High triglyceride levels are one marker of insulin resistance (13,14) and, therefore, could identify women in whom any insulin desensitizing effects of progestin-only contraception could be particularly deleterious to glucose regulation. Whether DMPA altered triglycerides or other markers of insulin resistance during follow-up was not assessed. Likewise, sample sizes were too small to test for a three-way interaction among triglycerides, DMPA use, and breast-feeding. Thus, we can only conclude that use of DMPA in women with relatively high triglyceride levels may increase the risk of diabetes after GDM, at least in one high-risk group.
One other group has published on DMPA use and the risks of diabetes (15) and weight gain (16). Both studies were in Navajo women. A case-control study by Kim et al. (15) showed that DMPA was associated with an odds ratio of 3.6 of developing diabetes compared with COCs in Navajo women aged 1850 years. No detailed breast-feeding information was reported. A 2-year longitudinal cohort study in the same population by Espey et al. (16) showed that DMPA use was associated with DMPA has been considered as a good contraceptive choice for women with medical problems, such as hypertension and cardiovascular diseases, that limit the use of estrogen. There is no indication that elevated blood pressure led to the choice of DMPA in this cohort, since baseline blood pressure levels were similar between the DMPA and COC groups and no women had baseline blood pressure >140/90 mmHg. Information on smoking was not collected, although most women in the patient population from which our study cohort was derived do not smoke and none had prior cardiovascular events. In summary, this prospective observational cohort study in Latino women with prior GDM revealed an increased risk of diabetes in women who elected to use DMPA compared with women who elected to use COCs. Much of the increased risk associated with DMPA was explained by the fact that women selected for DMPA use had clinical characteristics that placed them at increased risk for diabetes even before they started treatment. However, DMPA was associated with increased weight gain that may have slightly contributed to the increased risk for diabetes in women placed on the medication. In addition, use of DMPA during breast-feeding was associated with a more than twofold increase in the risk of diabetes compared with COC and DMPA without breast-feeding. DMPA also appeared to interact with baseline triglyceride levels, increasing the risk of diabetes that was readily detected at triglycerides >150 mg/dl in this study. Our findings in this observational study indicate a need for controlled studies to better define the risks of diabetes associated with the use of DMPA and other hormonal forms of contraception in women at high risk for type 2 diabetes. Pending the results of such studies, our findings suggest a need for caution when considering the use of DMPA in women with prior GDM. Careful monitoring of glucose levels is warranted in women who elect to use the drug, especially in the setting of breast-feeding and/or with high triglycerides.
This study was supported by grants R21-DK066243 and R01 DK-46374 from the National Institute of Diabetes and Digestive and Kidney Disease, National Institutes of Health. T.A.B. is supported by grant M01-RR43 and a Distinguished Clinical Scientist Award from the American Diabetes Association.
A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Received for publication October 11, 2005. Accepted for publication November 27, 2005.
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