Effect of combined oral contraceptives on glycosylated haemoglobin

Glycosylated haemoglobin (HbA), was measured in 164 Caucasian women aged 20-40 years who were using: (1) barrier contraceptive methods; (2) contraceptive pills with 30 micrograms ethinyloestradiol and 150 micrograms laevo-norgestrel; (3) contraceptive pills with 30-35 micrograms ethinyloestradiol and 0.5-1 mg norethisterone. Mean +/- 1 s.d. values for the three groups were 7.64 +/- 0.69, 7.56 +/- 0.56 and 7.27 +/- 0.74 respectively. Groups (1) and (2) did not differ significantly from one another but the mean value for group (3) was significantly lower than for the other groups (P less than 0.01). Age, percentage ideal body weight and smoking did not influence HbA, but the value was higher for parous than for nulliparous women (P = 0.02). These findings can be explained in terms of the known effects of oestrogens and progestogens on fasting blood glucose.