H A A M van Vliet

Catharina Hospital, Eindhoven, North Brabant, Netherlands

Are you H A A M van Vliet?

Claim your profile

Publications (10)55.65 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Use of combined hormonal contraceptives is associated with a three- to eight-fold increased risk of venous thrombosis compared with non-use. The thrombotic risk depends on the estrogen dose as well as the progestogen type. Use of hormonal contraceptives leads to resistance to activated protein C (APC), which may serve as marker for the risk of venous thrombosis. Hyperthyroidism is also associated with an increased risk of venous thrombosis, due to increased free Thyroxine (FT4) levels which cause a hypercoagulable state. The objective of this study was to evaluate the effects of hormonal contraceptives on levels of FT4, thyroid stimulating hormone (TSH) and thyroxine binding globulin (TBG), and to investigate the effects on APC resistance per contraceptive group. We measured FT4, TBG and TSH levels and APC resistance in 231 users of oral contraceptives. Users of the most thrombogenic hormonal contraceptives, i.e. containing desogestrel, cyproterone acetate or drospirenone, had higher TBG levels than users of less thrombogenic hormonal contraceptives, i.e. the levonorgestrel-containing intrauterine device. TSH levels were not significantly elevated and FT4 levels did not change. TBG levels were also associated with APC resistance. Use of hormonal contraceptives lead to elevated TBG levels, slightly elevated TSH levels and unchanged FT4 levels without causing a hyperthyroid state. Thus, the increased thrombotic risk during the use of hormonal contraceptives cannot be explained by a hyperthyroid state caused by use of these hormonal contraceptives.
    Thrombosis Research 01/2014; · 3.13 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Use of combined oral contraceptives is associated with a three- to six-fold increased risk of venous thrombosis. Hormonal contraceptives induce acquired resistance to activated protein C (APC), which predicts the risk of venous thrombosis. The biological basis of the acquired APC resistance is unknown. Free protein S (PS) and free tissue factor pathway inhibitor (TFPI) are the two main determinants of APC. Our objective was to assess the effect of both hormonal and non-hormonal contraceptives with different routes of administration on free TFPI and free PS levels. We conducted an observational study in 243 users of different contraceptives and measured APC sensitivity ratios (nAPCsr), free TFPI and free PS levels. Users of contraceptives with the highest risk of venous thrombosis as reported in recent literature, had the lowest free TFPI and free PS levels, and vice versa, women who used contraceptives with the lowest risk of venous thrombosis had the highest free TFPI and free PS levels. An association was observed between levels of free TFPI and nAPCsr, and between free PS and nAPCsr. The effect of oral contraceptives on TFPI and PS is a possible explanation for the increased risk of venous thrombosis associated with oral contraceptives.
    Thrombosis and Haemostasis 02/2013; 109(4). · 5.76 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effect of a combined oral contraceptive (COC) on sex hormone binding globulin (SHBG) levels may be an indicator for venous thrombosis risk of the COC involved [1,2]. SHBG is a plasma glycoprotein primarily produced in hepatocytes that binds the sex steroid hormones testosterone and 17β-estradiol but not ethinylestradiol. Users of COC containing a third generation progestagen have higher SHBG levels than second generation progestagen users [1,2] reflecting the difference in venous thrombosis risk. © 2012 International Society on Thrombosis and Haemostasis.
    Journal of Thrombosis and Haemostasis 11/2012; · 6.08 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Oral contraceptives (OC) containing different types of progestogens induce different sensitivities to activated protein C (APC) measured with the thrombin generation-based APC-resistance test. These differences in APC resistance may be the biological explanation for the differences in thrombotic risk of the various pills. The mechanistic basis of APC resistance observed in OC users is unknown. Our objective was to study the effect of OC on the two main determinants of the APC-resistance test, free protein S and free tissue factor pathway inhibitor (TFPI). We measured free protein S and free TFPI in 156 users of various types of OC. Users of desogestrel-containing OC, known to double the risk of thrombosis compared with levonorgestrel-containing OC, had lower free protein S (24 vs. 33 U dL(-1)) and TFPI free antigen (2.9 vs. 3.6 ng mL(-1)) levels than users of OC containing levonorgestrel. Women using cyproterone acetate-containing OC, known to confer a high thrombotic risk, had the lowest free protein S (19 U dL(-1)) and free TPFI antigen (2.5 ng mL(-1)) levels. Users of OC containing drospirenone had lower free protein S (23 U dL(-1)) and TFPI antigen levels (3.2 ng mL(-1)) than users of levonorgestrel-containing OC. Low free protein S and low free TFPI antigen levels were associated with an increased resistance to APC, an established risk factor for thrombosis. This study observed that the differences in APC resistance induced by OC containing different progestogens can at least in part be explained by different effects of OC on free protein S and TFPI.
    Journal of Thrombosis and Haemostasis 03/2008; 6(2):346-51. · 6.08 Impact Factor
  • J Visser, M Snel, H A A M Van Vliet
    [Show abstract] [Hide abstract]
    ABSTRACT: Adequate contraceptive advice is important in women with diabetes mellitus type 1 and 2 to reduce the risk of maternal and infant morbidity and mortality in unplanned pregnancies. A wide variety of contraceptives are available for these women. However hormonal contraceptives might influence carbohydrate and lipid metabolism and increase micro- and macrovascular complications. So caution in selecting a contraceptive method is required. To investigate whether progestogen-only, combined estrogen/progestogen or non-hormonal contraceptives differ in terms of effectiveness in preventing pregnancy, in their side effects on carbohydrate and lipid metabolism and in long-term complications such as micro- and macrovascular disease, when used in women with diabetes mellitus. The search was performed in MEDLINE, EMBASE, CENTRAL/CCTR, POPLINE, CINAHL, WorldCat, ECO, ArticleFirst, the Science Citation Index, the British Library Inside, and reference lists of relevant articles. Last search was performed in May 2005. In addition, experts in the field and pharmaceutical companies marketing contraceptives were contacted to identify published, unpublished or ongoing studies. Randomised and quasi-randomised controlled trials that studied women with diabetes mellitus comparing: 1. hormonal versus non-hormonal contraceptives. 2. progestogen-only versus estrogen/progestogen contraceptives. 3. contraceptives containing <50 microg estrogen versus contraceptives containing > or = 50 microg estrogen. 4. contraceptives containing 'first'-, 'second'- and 'third'-generation progestogens, drospirenone and cyproterone acetate. Principal outcomes were contraceptive effectiveness, diabetes control, lipid metabolism and micro- and macrovascular complications. Two investigators evaluated the titles and abstracts from the literature search. Quality assessment was performed independently with discrepancies resolved by discussion or consulting a third reviewer. Because the trials differed in studied contraceptives, participant characteristics and methodological quality, we could not combine the data in a meta-analysis. The trials were therefore examined on an individual basis and narrative summaries were provided. Three randomised controlled trials were included. Only one was of good methodological quality. It compared the influence of levonorgestrel-releasing IUD versus copper-IUD on carbohydrate metabolism in women with type 1 diabetes mellitus. No difference was found in daily insulin requirement, glycosylated hemoglobin (HbA1c) or fasting blood sugar after twelve months. The other two trials were of limited methodological quality. Both compared progestogen-only pills with different estrogen/progestogen combinations. The trials reported blood glucose levels to remain stable during treatment with most regimens. Only high-dose combined oral contraceptives were found to slightly impair glucose homeostasis. Combined oral contraceptives also appeared to have a minor adverse effect on lipid metabolism whereas progestogen-only contraceptives slightly improved lipid-metabolism. Only one study reported on micro- and macrovascular complications. No signs or symptoms of thromboembolic incidents or visual disturbances were observed. However study duration was short. Minor adverse effects were reported in one study. The trial found progestogen-only pills to cause more bleeding irregularities when compared with combined oral contraceptives. Unintended pregnancies were not observed during any of the studies. The three included randomised controlled trials in this systematic review provided insufficient evidence to assess whether progestogen-only and combined contraceptives differ from non-hormonal contraceptives in diabetes control, lipid metabolism and complications. Two of the three studies were of limited methodological quality, sponsored by pharmaceutical companies and described surrogate outcomes. Ideally, an adequately reported, high-quality randomised controlled trial analysing both intermediate outcomes (i.e. glucose and lipid metabolism) and true clinical endpoints (micro- and macrovascular disease) in users of combined, progestogen-only and non-hormonal contraceptives should be conducted. However, due to the low incidence of micro- and macrovascular disease and accordingly the large sample size and follow-up period needed to observe differences in risk, a randomised controlled trial might not be the ideal design.
    Cochrane database of systematic reviews (Online) 02/2006; · 5.70 Impact Factor
  • H A A M Van Vliet, D A Grimes, F M Helmerhorst, K F Schulz
    [Show abstract] [Hide abstract]
    ABSTRACT: Side effects caused by oral contraceptives discourage compliance with, and continuation of, oral contraceptives. Three approaches have been used to decrease these adverse effects: reduction of steroid dose, development of new steroids, and new formulas and schedules of administration. The third strategy led to the biphasic oral contraceptive pill. To compare biphasic with monophasic oral contraceptives in terms of efficacy, cycle control, and discontinuation due to side effects. Our a priori hypotheses were: (a) biphasic oral contraceptives are less effective than monophasic oral contraceptives in preventing pregnancy; (b) biphasic oral contraceptives cause more side effects, give poorer cycle control, and have lower continuation rates. We searched the computerized databases MEDLINE, EMBASE, POPLINE, LILACS and CENTRAL. In addition, we searched the reference lists of all potentially relevant articles and book chapters. We also contacted the authors of relevant studies and pharmaceutical companies in Europe and the USA. We included randomized controlled trials comparing any biphasic with any monophasic oral contraceptive when used to prevent pregnancy. We examined the studies found during the various literature searches for possible inclusion and assessed their methodology using Cochrane guidelines. We contacted the authors of all included studies and possibly randomized studies for supplemental information about methodology and outcome. We entered the data into RevMan, and calculated Peto odds ratios for the incidence of intermenstrual bleeding, absence of withdrawal bleeding, and study discontinuation due to intermenstrual bleeding. Only one trial of limited quality compared a biphasic and monophasic preparation. Percival-Smith 1990 examined 533 user cycles of a biphasic pill (500 microg norethindrone/35 microg ethinyl estradiol for 10 days, followed by 1000 microg norethindrone/35 microg ethinyl estradiol for 11 days; Ortho 10/11) and 481 user cycles of a monophasic contraceptive pill (1500 microg norethindrone acetate/30 microg ethinyl estradiol daily; Loestrin). The study found no significant differences in intermenstrual bleeding, amenorrhea and study discontinuation due to intermenstrual bleeding between the biphasic and monophasic oral contraceptive pills. Conclusions are limited by the identification of only one trial, the methodological shortcomings of that trial, and the absence of data on accidental pregnancies. However, the trial found no important differences in bleeding patterns between the biphasic and monophasic preparations studied. Since no clear rationale exists for biphasic pills and since extensive evidence is available for monophasic pills, the latter are preferred.
    Cochrane database of systematic reviews (Online) 02/2006; · 5.70 Impact Factor
  • H A A M Van Vliet, D A Grimes, F M Helmerhorst, K F Schulz
    [Show abstract] [Hide abstract]
    ABSTRACT: Side effects caused by oral contraceptives discourage compliance with, and continuation of, oral contraceptives. A suggested disadvantage of biphasic compared to triphasic oral contraceptive pills is an increase in breakthrough bleeding. We conducted this systematic review to examine this potential disadvantage. To compare biphasic with triphasic oral contraceptives in terms of efficacy, cycle control, and discontinuation due to side effects. We searched MEDLINE, EMBASE, POPLINE, LILACS and CENTRAL. We searched the reference lists of relevant articles and book chapters. We also contacted the authors of relevant studies and pharmaceutical companies in Europe and the USA. We included randomized controlled trials comparing any biphasic with any triphasic oral contraceptive when used to prevent pregnancy. We examined the studies found during the searches for possible inclusion and assessed methodological quality using Cochrane guidelines. We contacted the authors of included studies and of possibly randomized studies for supplemental information about the methods and outcomes. We entered the data into RevMan. We calculated Peto odds ratios for incidence of discontinuation due to medical reasons, intermenstrual bleeding, and absence of withdrawal bleeding. Only two trials of limited quality met our inclusion criteria. Larranaga 1978 compared two biphasic pills and one triphasic pill, each containing levonorgestrel and ethinyl estradiol. No important differences emerged, and the frequency of discontinuation due to medical problems was similar with all three pills. Percival-Smith 1990 compared a biphasic pill containing norethindrone (Ortho 10/11) with a triphasic pill containing levonorgestrel (Triphasil) and with another triphasic containing norethindrone (Ortho 7/7/7). The biphasic pill had inferior cycle control compared with the levonorgestrel triphasic. The odds ratio of cycles with intermenstrual bleeding was 1.7 (95% CI 1.3 to 2.2) for the biphasic compared with the triphasic levonorgestrel pill. The odds ratio of cycles without withdrawal bleeding was 6.5 (95% CI 3.1 to 13). In contrast, cycle control with the biphasic pill was comparable to that of the triphasic containing the same progestin (norethindrone). The available evidence is limited and the internal validity of these trials is questionable. Given the high losses to follow up, these reports may even be considered observational. Given that caveat, the biphasic pill containing norethindrone was associated with inferior cycle control compared with the triphasic pill containing levonorgestrel. The choice of progestin may be more important than the phasic regimen in determining bleeding patterns.
    Cochrane database of systematic reviews (Online) 02/2006; · 5.70 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Side effects of oral contraceptive pills (OCs) discourage adherence to and continuation of OC regimens. Strategies to decrease adverse effects led to the introduction of the triphasic OC in the 1980s. Whether triphasic OCs have higher accidental pregnancy rates than monophasic pills is unknown. Nor is it known if triphasic pills give better cycle control and fewer side effects than the monophasic pills. To compare triphasic OCs with monophasic OCs in terms of efficacy, cycle control, and discontinuation due to side effects. We searched the computerized databases of MEDLINE, EMBASE, POPLINE, LILACS and CENTRAL. Additionally, we searched the reference lists of relevant articles and book chapters. We also contacted researchers and pharmaceutical companies in Europe and the U.S. to identify other trials not found in our search. We included randomized controlled trials (RCTs) comparing any triphasic OC with any monophasic pill used to prevent pregnancy. Interventions had to include at least three treatment cycles. We assessed the studies found in the literature searches for possible inclusion and for their methodological quality. We contacted the authors of all included studies and of possibly randomized trials for supplemental information about the methods and outcomes studied. We entered the data into RevMan 4.2 and calculated odds ratios for the outcome measures of efficacy, breakthrough bleeding, spotting, withdrawal bleeding and discontinuation. Of 21 trials included, 18 examined contraceptive effectiveness: the triphasic and monophasic preparations did not differ significantly. Several trials reported favorable bleeding patterns, i.e. less spotting, breakthrough bleeding or amenorrhea, in triphasic versus monophasic OC users. However, meta-analysis was generally not possible due to differences in measuring and reporting the cycle disturbance data as well as differences in progestogen type and hormone dosages. No significant differences were found in the numbers of women who discontinued due to medical reasons, cycle disturbances, intermenstrual bleeding or adverse events. The available evidence is insufficient to determine whether triphasic OCs differ from monophasic OCs in effectiveness, bleeding patterns or discontinuation rates. Therefore, we recommend monophasic pills as a first choice for women starting OC use. Large, high-quality RCTs that compare triphasic and monophasic OCs with identical progestogens are needed to determine whether triphasic pills differ from monophasic OCs. Future studies should follow the WHO recommendations on recording menstrual bleeding patterns and the CONSORT reporting guidelines.
    Cochrane database of systematic reviews (Online) 02/2006; · 5.70 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The postcoital test has poor diagnostic and prognostic characteristics. Nevertheless, some physicians believe it can identify scanty or abnormal mucus that might impair fertility. One way to avoid 'hostile' cervical mucus is intrauterine insemination. With this technique, the physician injects sperm directly into the uterine cavity through a small catheter passed through the cervix; the theory is to bypass the "hostile" cervical mucus. Although most gynaecological societies do not endorse use of intrauterine insemination for hostile cervical mucus, some physicians consider it an effective treatment for women with infertility thought due to cervical mucus problems. The aim of this review was to determine the effectiveness of intrauterine insemination with or without ovarian stimulation in women with cervical hostility who failed to conceive. We searched Cochrane Central Register of Controlled Trials (CENTRAL) on The Cochrane Library Issue 2, 2005, MEDLINE (1966 to June 2005), EMBASE (1980 to June 2005), POPLINE (to June 2005) and LILACS (to June 2005). In addition, we contacted experts and searched the reference list of relevant articles and book chapters. We included randomized and quasi-randomized controlled trials comparing intrauterine insemination with intercourse timed at the presumed fertile period. Participants were women with cervical hostility who failed to conceive for at least one year. We assessed the titles and abstracts of 386 publications and two reviewers independently abstracted data on methods and results from five studies identified for inclusion. The main outcome is pregnancy rate per couple. We did not pool the outcomes of the included five studies in a meta-analysis due to the methodological quality of the trials and variations in the patient characteristics and interventions. Narrative summaries of the outcomes are provided. Each study was too small for a clinically relevant conclusion. None of the studies provided information on important outcomes such as spontaneous abortion, multiple pregnancies, and ovarian hyperstimulation syndrome. There is no evidence from the published studies that intrauterine insemination is an effective treatment for cervical hostility. Given the poor diagnostic and prognostic properties of the postcoital test and the observation that the test has no benefit on pregnancy rates, intrauterine insemination (with or without ovarian stimulation) is unlikely to be a useful treatment for putative problems identified by postcoital testing.
    Cochrane database of systematic reviews (Online) 02/2005; · 5.70 Impact Factor
  • Source
    H A A M van Vliet, T A Winkel, I Noort, J Rosing, F R Rosendaal
    Journal of Thrombosis and Haemostasis 12/2004; 2(11):2060-2. · 6.08 Impact Factor