Background: The prevalence of obesity is increasing worldwide. The treatment of morbid obesity is dominated by bariatric surgery, for example Roux-en-Y gastric bypass (RYGB) surgery. If other contraceptive options are available, women with obesity should not be prescribed combined hormonal contraceptives due to the obesity-related increased risk of venous thromboembolism. Women are advised not to become pregnant during the first 12-18 months after RYGB surgery. There is a lack of knowledge of what type of contraceptive methods women with obesity are prescribed and whether they experience more or different side effects compared to normal-weight women. It is not known if the absorption and pharmacokinetic profile of progestins are affected by RYGB. The aim of this thesis was to investigate the pattern of contraceptive use in women with obesity, what type of contraceptive counselling was given to women in relation to RYGB, and whether the pharmacokinetics of two different progestins were affected by RYGB surgery.

Material and Methods: Paper I is a retrospective cohort study analysing the patterns of contraceptive prescription, adverse effects, duration of treatment, reasons for discontinuation and bleeding pattern in 371 women with obesity compared with 744 normal-weight women. Medical records were scrutinised from 1 Jan 2010 until 31 Dec 2014. Paper II is based on a questionnaire sent to 987 women who had undergone RYGB during 2010. The questionnaire concerned preoperative and present contraceptive use, contraceptive counselling in relation to surgery and what type of recommendations they had received regarding pregnancy after RYGB. Papers III and IV are experimental studies investigating the pharmacokinetics of desogestrel (etonogestrel) and levonorgestrel in relation to RYGB.

Results and conclusions: The most commonly prescribed contraceptive method for women with obesity was the progestin-only pill but many women with obesity were prescribed combined hormonal contraceptives despite the current recommendations of cautious prescription of oestrogen-containing methods. There were no differences in adherence to contraceptive method between women with obesity and normal-weight women. Despite the uncertainties regarding absorption, almost 10 % of women continued using oral contraceptives after RYGB. Nearly 40% were not aware of the recommendation to avoid pregnancy in the first year after RYGB and almost one third did not use any contraception during this period. This could be due to a lack of information or that the women did not retain the given information to avoid pregnancy. We found no clinically significant differences in the steady state pharmacokinetics of desogestrel before compared with after RYGB, or in single dose pharmacokinetics of levonorgestrel in women with BMI< 30 having undergone RYGB compared with BMI-matched non-operated women. This suggests that oral contraceptives containing desogestrel and levonorgestrel might be used after RYGB surgery.