A Cochrane review «»1 «Gallo MF, Nanda K, Grimes DA et al. 20 µg versus >...»1 included 21 studies. English-language reports of randomized controlled trials that compare a COC containing 20 mcg EE with a COC containing >20 mcg EE were eligible. No differences were found in contraceptive effectiveness for the 13 COC pairs for which this outcome was reported. Several COCs containing 20 mcg EE resulted in higher rates of early trial discontinuation (overall and due to adverse events such as irregular bleeding) as well as increased risk of bleeding disturbances (both amenorrhea/infrequent bleeding and irregular, prolonged, frequent bleeding, or breakthrough bleeding or spotting) than their higher-estrogen comparison pills.
A database cohort study «. ...»2 included 4 945 088 women aged 15-49 years. 1800 pulmonary embolisms (33 per 100 000 women years), 1046 ischaemic strokes (19 per 100 000 women years), and 407 myocardial infarctions (7 per 100 000 women years) were observed. After adjustment for progestogen and risk factors, the relative risks for women using low dose oestrogen (20 µg v 30-40 µg) were 0.75 (95% CI 0.67 to 0.85) for pulmonary embolism, 0.82 (0.70 to 0.96) for ischaemic stroke, and 0.56 (0.39 to 0.79) for myocardial infarction. After adjustment for oestrogen dose and risk factors, desogestrel and gestodene were associated with statistically significantly higher relative risks for pulmonary embolism (2.16, 1.93 to 2.41 and 1.63, 1.34 to 1.97, respectively) compared with levonorgestrel.
Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment, lack of blinding, and more than 20% loss to follow up).