***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: The objective of this study was to assess the influence of oral contraceptives ( OCs ) on the risk of venous thromboembolism ( VTE ) in young women . A 5-year case-control study including all Danish hospitals was conducted . All women 15 - 44 years old , suffering a first ever deep venous thrombosis or a first pulmonary embolism ( PE ) during the period January 1 , 1994 , to December 30 , 1998 , were included . Controls were selected annually , 600 per year in 1994 - 1995 and 1200 per year 1996 - 1998 . Response rates for cases and controls were 87.2 % and 89.7 % , respectively . After exclusion of nonvalid diagnoses , pregnant women , and women with previous thrombotic disease , 987 cases and 4054 controls were available for analysis . A multivariate , matched analysis was performed . Controls were matched to cases within 1-year age b and s. Adjustment was made for confounding influence ( if any ) from the following variables : age , year , body mass index , length of OC use , family history of VTE , cerebral thrombosis or myocardial infa rct ion , coagulopathies , diabetes , years of schooling , and previous birth . The risk of VTE among current users of OCs was primarily influenced by duration of use , with significantly decreasing odds ratios ( OR ) over time : < 1 year , 7.0 ( 5.1 - 9.6 ) ; 1 - 5 years , 3.6 ( 2.7 - 4.8 ) ; and > 5 years , 3.1 ( 2.5 - 3.8 ) , all compared with nonusers of OCs . After adjustment for confounders , current use of OCs with second- ( levonorgestrel or norgestimate ) and third- ( desogestrel or gestodene ) generation progestins when compared with nonuse result ed in ORs for VTE of 2.9 ( 2.2 - 3.8 ) and 4.0 ( 3.2 - 4.9 ) , respectively . After adjusting for progestin types and length of use , the risk decreased significantly with decreasing estrogen dose . With 30 - 40 microg as reference , 20 and 50 microg products implied ORs of 0.6 ( 0.4 - 0.9 ) and 1.6 ( 0.9 - 2.8 ) , respectively ( p(trend ) = 0.02 ) . After correction for duration of use and differences in estrogen dose , the third/second-generation risk ratio was 1.3 ( 1.0 - 1.8 ; p < 0.05 ) . In conclusion , use of OCs was associated significantly to the risk of VTE . The risk among current users was reduced by more than 50 % during the first years of use . The risk increased more than 100 % with increasing estrogen dose , and the difference in risk between users of third- and second-generation OCs , after correction for length of use and estrogen dose , was 33 % To test the efficacy and tolerance of progestagens as contraceptives in systemic lupus erythematosus ( SLE ) , 200 mg IM norethisterone enanthate was administered to 10 patients , 0.03 mg/day oral levonorgestrel to 15 patients and they were compared with 18 control patients . There were 4 episodes of active SLE in 48 patient-months on norethisterone enantate and 6 episodes in 122 patient-months on levonorgestrel as compared with 9 episodes of active disease in 298 control patient-months ( p = ns ) . There were no pregnancies and intermenstrual bleeding led to discontinuation of medication in 30 % of patients . Progestagens may be an alternative contraceptive method in SLE Epidemiologic studies conducted in the 1960s and 1970s [ 1 - 4 ] showed an increased risk for stroke as well as myocardial infa rct ion and venoocclusive disease in women who used oral contraceptives containing more than 50 g of ethinyl estradiol .  These reports spurred the development of oral contraceptive pills containing less than 50 g of ethinyl estradiol . Initial studies of cerebrovascular risk in users of low-dose oral contraceptives  produced conflicting results : Some investigators found increased risks [ 5 , 6 ] , and others found no increased risk [ 7 ] . In addition , few data are available on whether the risk for stroke associated with use of low-dose oral contraceptives is influenced by the type of progestin present in these medications . In the United States , most currently available low-dose oral contraceptives contain either norethindrone-type progestins ( norethindrone , norethindrone acetate , ethynodiol diacetate , or norethynodrel ) or norgestrel-type progestins ( norgestrel or levonorgestrel ) . It has been proposed that the levonorgestrel component of oral contraceptives may offset the cardiovascular benefits that arise from the use of low doses of estrogen [ 8 , 9 ] , but little empirical research has addressed this hypothesis . A recent study [ 10 ] conducted among the members of the Northern and Southern California Kaiser Permanente medical care programs reported that the use of low-dose oral contraceptives available in the United States was not associated with an increased risk for either hemorrhagic or ischemic stroke , regardless of progestin type . In that study , past users of oral contraceptives were at reduced risk for ischemic stroke but not hemorrhagic stroke ; this finding was consistent with findings from an earlier study of cerebral thromboembolic attack [ 5 ] but differed from those in a previous study of subarachnoid hemorrhage [ 7 ] . To provide information on the occurrence of stroke among  oral contraceptive users in a U.S. community , we report the results of a population -based casecontrol study done in a defined geographic region of western Washington State . Methods The source population for our study was women 18 to 44 years of age residing in King , Pierce , or Snohomish counties , Washington , between 1 July 1991 and 28 February 1995 . This represented approximately 2.2 million women-years at risk , according to population estimates provided by the State of Washington Office of Financial Management . Definition and Ascertainment of Case- Patients and Controls Eligible case- patients were women in the source population with a first diagnosis of fatal or nonfatal stroke and without a history of major coronary heart disease , such as myocardial infa rct ion , angina , or congestive heart failure . We identified potential case- patients through regular review and abstract ion of 1 ) medical records containing cerebrovascular disease discharge diagnoses at all 34 acute care hospitals within the study region and 2 ) death certificates filed at county health departments . These sources were supplemented with monthly letters sent to all neurologists , neurosurgeons , and physiatrists in the region . We defined stroke as the new , rapid onset of symptoms and signs consistent with loss of cerebral function that lasted at least 24 hours and could not be ascribed to subdural hematoma ; brain tumor ; infection ; seizure ; or other neurologic disease , such as multiple sclerosis . A neurologist review ed the records to confirm the diagnosis of stroke and to classify confirmed strokes as either arterial or venous in origin . Arterial strokes were further classified as hemorrhages , ischemic events , or other [ a category that included arterial dissections ] . Aneurysmal bleeding was defined as a hemorrhagic stroke in which the diagnostic workup or autopsy showed 1 ) blood in the subarachnoid space with or without a demonstrated aneurysm and no evidence of arteriovenous malformation or 2 ) an aneurysm with blood in other locations , such as the parenchyma or ventricles , and no evidence of arteriovenous malformation . Eligible controls were women 18 to 44 years of age who were residents of King , Pierce , or Snohomish counties during the case-diagnosis period and had no history of major coronary or cerebrovascular disease . We identified a sample of these women by using r and om-digit dialing [ 11 ] . Data Collection Participating case- patients and controls were interviewed in person by trained female interviewers who used a structured question naire that elicited information about cardiovascular risk factors . We used the reproductive calendar method and color photographs of all oral contraceptive pills marketed in the United States to help women recall date s and specific br and s of oral contraceptives used . All interview questions elicited information about the time period before each participant 's reference date , which was the date of stroke for a case-patient and a date assigned at r and om from among the potential stroke occurrence date s for a control . We also sought in-person interviews with proxy respondents for case- patients who had died or were mentally impaired . To evaluate the quality of information received from proxy respondents , we did in-person interviews with proxy respondents for case- patients who had not died and who were not mentally impaired and for a r and om one third of controls [ 12 ] . The interviews with proxy respondents contained the same questions asked of the case- patients and controls . Proxy respondents and participants were not interviewed in each other 's presence . Statistical Analysis A woman was considered to be a current user of oral contraceptives  if she or her proxy reported that she had been taking these pills within a month of her reference date . She was considered to be a past user if she had used oral contraceptives but was not using them at that time . The remaining women were classified as having never used oral contraceptives . We classified current users of oral contraceptives according to whether the pill was a low-dose ( < 50 g of ethinyl estradiol ) or a high-dose ( 50 g of ethinyl estradiol ) formulation . No women reported current use of pills containing more than 50 g of ethinyl estradiol . We used unconditional logistic regression models to compute estimated odds ratios and 95 % CIs [ 13 ] . We excluded from all analyses women who were pregnant at the reference date ( 5 case- patients , 14 controls ) and women for whom information on use of oral contraceptives was missing ( 6 case- patients , 24 controls ) . Thus , 173 case- patients and 485 controls were included in the analysis . Of the case- patients , 102 were classified as having had hemorrhagic stroke , 60 were classified as having had ischemic stroke , and 11 were classified as having had other types of stroke . Sixty-nine of the hemorrhagic strokes were classified as cases of aneurysmal bleeding . In all analyses , we examined the potential confounding effect of known or suspected cerebrovascular risk factors . We initially adjusted all odds ratios for age ( in years ) , race , treated hypertension , and cigarette smoking ; we then examined whether further adjustment for other characteristics changed the estimates of association . We also conducted subanalyses in which case- patients who did not have residential telephones were excluded . To determine whether the risk for total stroke associated with oral contraceptive use varied according to other cardiovascular risk factors , we estimated odds ratios separately by age , cigarette smoking status , obesity ( body mass index 27.3 kg/m2 or < 27.3 kg/m2 ) , and among women not receiving treatment for hypertension . Results Case- Patients and Controls We identified 249 women who met the eligibility criteria for stroke : One hundred forty-one were classified as having had hemorrhagic stroke , 95 as having had ischemic stroke , 10 as having had arterial dissection , and 3 as having had venous stroke . The results of computed tomography , magnetic resonance imaging , or both were available for 92 % of patients with stroke diagnoses . Ninety-one of the 141 patients with hemorrhagic strokes were further classified as having had strokes as a result of aneurysms . Of the 198 patients who were alive and not mentally impaired as a result of their strokes , 149 ( 75.3 % ) participated in the study . Most nonparticipation was due to patient refusal ( n = 30 ) or inability to locate the patient ( n = 13 ) . For the 51 eligible patients with stroke who died or were mentally impaired as a result of the stroke , we attempted to identify and recruit proxy respondents . Through r and om-digit dialing , we completed a household census for 94.9 % of the residences contacted . Among the eligible women identified , we attempted to recruit 691 who were similar in age to the patients with stroke . Six of the potential controls were excluded because of a history of major coronary heart disease or stroke , and one was excluded because she was unable to communicate in English . Of the remaining 684 women , 526 were recruited into the study , for an estimated overall response rate of 73.0 % ( 526 684 0.949 ) . Proxy Respondents We recruited proxy respondents for 34 of the 51 patients with stroke who had died or were mentally impaired , 106 of the 149 patients with stroke who had not died and were not mentally impaired , and 160 of the 273 controls whom we had selected at r and om . Approximately 80 % of the proxy respondents for both case- patients and controls were spouses or sexual partners ( 54.3 % of proxy respondents for case- patients ; 64.4 % of proxy respondents for controls ) , mothers ( 15.7 % of proxy respondents for case- patients ; 10.0 % of proxy respondents for controls ) , or roommates or close friends ( 10.7 % of proxy respondents for case- patients ; 8 
    Output:
    
Studies did not find increased odds of VTE with POPs for contraceptive purpose s , implants or LNG-IUDs nor were there increased odds of stroke or AMI with any POCs .
CONCLUSION The majority of evidence identified by this systematic review did not suggest an increase in odds for venous or arterial events with use of most POCs .
Any increase in risk likely translates to a small increase in absolute numbers of thrombotic events at the population level