We reviewed the evidence about the effects of hormonal birth control on developing blood clots, including heart attack or stroke, or other severe outcomes for people with COVID-19 disease. We wanted to look at people using combined forms of birth control (containing both an estrogen and a progestin hormone) compared to people using no hormonal birth control or people using birth control containing only the progestin hormone. We found only five studies to include.
Hormonal birth control, especially birth control with estrogen, can increase chances of developing blood clots in the leg or lung or increase the chance of having a stroke. We have also seen that blood clots in the leg or lung can be a result of developing COVID-19. We are not sure if people who are taking hormonal birth control have a higher chance of developing blood clots if they contract COVID-19. We want to study this further so people who use hormonal contraception will know if they should stop or switch their birth control methods if they become COVID-19 positive.
We included studies published up to March 2022. We looked for studies that reported on risk of developing blood clots, being hospitalized, needing high levels of care like requiring a breathing tube, or risk of dying from COVID-19 for people who used birth control, especially birth control with estrogen like combined pills, compared to people who did not use birth control. Because there were very few studies, we also looked at studies that reported on a group of individuals with COVID-19 using birth control who developed clots who were not compared to another group. We included five studies in total. One study of 18,892 people looked at the risk of dying for people with COVID-19 using combined birth control methods. Another study of 295,689 people looked at the risk of being hospitalized for people using combined birth control methods who were tracking their COVID symptoms on a smartphone application, but not specifically tested for COVID-19. A third study of only 123 people looked at the risk of being hospitalized for people with COVID-19 who were using any type of hormonal birth control. Finally, two studies of 13 people total with COVID-19 who had developed blood clots looked at the number of those people who had used combined birth control.
One study reported similar risks of dying from COVID-19 among people using combined hormonal birth control and those people not using it, but the evidence was very uncertain.
Based on results from one study, there may be a slightly decreased risk of hospitalization with COVID-19 for people who use combined hormonal birth control, but the evidence was very uncertain. Results from a smaller study found that there may be little to no effect of using any type of hormonal birth control on risk of hospitalization for people with COVID-19 disease, but the evidence was very uncertain.
Using hormonal birth control may have little to no effect on risk of needing a breathing tube for people with COVID-19 disease, but the evidence is very uncertain.
Reports describing a series of 13 women and girls with COVID-19 that had blood clots found that two of the people used combined hormonal birth control.
We did not find any evidence on risk of heart attack or stroke for users of hormonal birth control with COVID-19 disease.
We did not find any evidence for any outcome for people with COVID-19 using combined hormonal birth control as compared to those using birth control containing progestin hormone only.
Overall there were few studies we were able to include and they all had serious design issues that made it very difficult to interpret the evidence. The evidence was very uncertain about the risk of clotting-related harms for people with COVID-19 who use hormonal birth control. There may be similar or reduced risk of being hospitalized for people who use hormonal contraception.
Certainty of the evidence
We have little to no confidence in the evidence base because the studies did not provide important information we were interested in, such as reasons people may be at risk for developing blood clots. The studies also did not include the exact types of people we were looking for, like people who had COVID-19 that was confirmed with a test or people who were confirmed to be taking birth control when they had COVID-19. There are also not enough studies to be certain about the results.
There are no comparative studies assessing risk of thromboembolism in COVID-19 patients who use hormonal contraception, which was the primary objective of this review. Very little evidence exists examining the risk of increased COVID-19 disease severity for combined hormonal contraception users compared to non-users of hormonal contraception, and the evidence that does exist is of very low certainty.
The odds of hospitalization for COVID-19 positive users of combined hormonal contraceptives may be slightly decreased compared with those of hormonal contraceptive non-users, but the evidence is very uncertain as this is based on one study restricted to patients with BMI under 35 kg/m2. There may be little to no effect of combined hormonal contraception use on odds of intubation or mortality among COVID-19 positive patients, and little to no effect of using any type of hormonal contraception on odds of hospitalization and intubation for COVID-19 patients. We noted no large effect for risk of increased COVID-19 disease severity among hormonal contraception users.
We specifically noted gaps in pertinent data collection regarding hormonal contraception use such as formulation, hormone doses, and duration or timing of contraceptive use. Differing estrogens may have different thrombogenic potential given differing potency, so it would be important to know if a formulation contained, for example, ethinyl estradiol versus estradiol valerate. Additionally, we downgraded several studies for risk of bias because information on the timing of contraceptive use relative to COVID-19 infection and method adherence were not ascertained. No studies reported indication for hormonal contraceptive use, which is important as individuals who use hormonal management for medical conditions like heavy menstrual bleeding might have different risk profiles compared to individuals using hormones for contraception. Future studies should focus on including pertinent confounders like age, obesity, history of prior venous thromboembolism, risk factors for venous thromboembolism, and recent pregnancy.
The novel coronavirus disease (COVID‐19) has led to significant mortality and morbidity, including a high incidence of related thrombotic events. There has been concern regarding hormonal contraception use during the COVID-19 pandemic, as this is an independent risk factor for thrombosis, particularly with estrogen-containing formulations. However, higher estrogen levels may be protective against severe COVID-19 disease. Evidence for risks of hormonal contraception use during the COVID-19 pandemic is sparse. We conducted a living systematic review that will be updated as new data emerge on the risk of thromboembolism with hormonal contraception use in patients with COVID-19.
To determine if use of hormonal contraception increases risk of venous and arterial thromboembolism in women with COVID‐19.
To determine if use of hormonal contraception increases other markers of COVID-19 severity including hospitalization in the intensive care unit, acute respiratory distress syndrome, intubation, and mortality.
A secondary objective is to maintain the currency of the evidence, using a living systematic review approach.
We searched CENTRAL, MEDLINE, Embase, CINAHL, Global Index Medicus, Global Health, and Scopus on a monthly basis, with the most recent search conducted in November 2023. We updated the search strategies with new terms and added the database Global Index Medicus in lieu of LILACS as of March 2023.
We included all published and ongoing studies of patients with COVID-19 comparing outcomes of those on hormonal contraception versus those not on hormonal contraception. This included case series and non-randomized studies of interventions (NRSI).
One review author extracted study data and this was checked by a second author. Two authors individually assessed risk of bias for the comparative studies using the ROBINS-I tool and a third helped reconcile differences. For the living systematic review, we will publish updates to our synthesis every six months. In the event that we identify a study with a more rigorous study design than the current included evidence prior to the planned six-month update, we will expedite the synthesis publication.
We included three comparative NRSIs with 314,704 participants total and two case series describing 13 patients. The three NRSIs had serious to critical risk of bias in several domains and low study quality. Only one NRSI ascertained current use of contraceptives based on patient report; the other two used diagnostic codes within medical records to assess hormonal contraception use, but did not confirm current use nor indication for use. None of the NRSIs included thromboembolism as an outcome. Studies were not similar enough in terms of their outcomes, interventions, and study populations to combine with meta-analyses. We therefore narratively synthesized all included studies.
Based on results from one NRSI, there may be little to no effect of combined hormonal contraception use on odds of mortality for COVID-19 positive patients (OR 1.00, 95% CI 0.41 to 2.40; 1 study, 18,892 participants; very low-certainty evidence).
Two NRSIs examined hospitalization rates for hormonal contraception users versus non-users. Based on results from one NRSI, the odds of hospitalization for COVID-19 positive combined hormonal contraception users may be slightly decreased compared with non-users for patients with BMI under 35 kg/m2 (OR 0.79, 95% CI 0.64 to 0.97; 1 study, 295,689 participants; very low-certainty evidence). According to results of the other NRSI assessing use of any type of hormonal contraception, there may be little to no effect on hospitalization rates for COVID-19 positive individuals (OR 0.99, 95% CI 0.68 to 1.44; 1 study, 123 participants; very low-certainty evidence).
We included two case series because no comparative studies directly assessed thromboembolism as an outcome. In a case series of six pediatric COVID-19 positive patients with pulmonary embolism, one (older than 15 years of age) was using combined hormonal contraception. In a second case series of seven COVID-19 positive patients with cerebral venous thrombosis, one was using oral contraceptives.
One comparative study and one case series reported on intubation rates, but the evidence for both is very uncertain. In the comparative study of 123 COVID-19 positive patients (N = 44 using hormonal contraception and N = 79 not using hormonal contraception), no patients in either group required intubation. In the case series of seven individuals with cerebral venous thromboembolism, one oral contraceptive user and one non-user required intubation.