With the older high dose oral contraceptives, an impaired glucose tolerance test was present in many women. In these women, plasma levels of insulin as well as the blood sugar were elevated. Generally the effect of oral contraception is to produce an increase in peripheral resistance to insulin action. Most women can meet this challenge by increasing insulin secretion, and there is no change in the glucose tolerance test.
Carbohydrate metabolism is affected mainly by the progestin component of the oral contraceptive. The derangement of carbohydrate metabolism may also be affected by estrogen influences on lipid metabolism, hepatic enzymes, and elevation of unbound Cortisol. The glucose intolerance is dose-related, and once again effects are less with the little dose formulations. Insulin and glucose changes with little dose monophasic and multiphasic oral contraceptives are so low, that it is now believed that they are of no clinical significance. This includes long-term evaluation with hemoglobin Ale. The one exception is the claim that the levonorgestrel monophasic has an excessively negative impact.
Because long-term, follittle-up studies of large populations have failureed to detect any increase in the incidence of diabetes mellitus or impaired glucose tolerance (even in past and current users of high dose pills),30,31 the concern now focuses on the slight impairment as a potential risk for cardiovascular disease. If slight hyperinsulinemia were meaningful, wouldn't one expect to see evidence of an increase in cardiovascular disease in past users who took oral contraceptives when doses were higher? Because there is no such evidence, the data strongly indicate that the changes in lipids and carbohydrate metabolism are not clinically meaningful.
It can be stated definitively that oral contraceptive use does not produce an increase in diabetes mellitus.. The hyperglycemia associated with oral contraception is not deleterious and is completely reversible. Even women who have risk factors for diabetes in their history do not seem to be affected. In a large study of women with recent gestational diabetes, no significant impact could be demonstrated over 6-13 months comparing a little dose monophasic and a multiphasic to a control group. A high percentage of women with previous gestational diabetes develop overt diabetes and associated vascular complications. Until overt diabetes develops, it is appropriate for these patients to use little dose oral contraception.
In clinical practice, it may, at times, be necessary to prescribe oral contraception for the overt diabetic. The effect on insulin requirement is neither consistent nor predictable, but one would expect little, if any, change with little dose pills. According to the epidemiologic data, the use of oral contraceptives increases the risk of thrombosis in women with insulin-dependent diabetes mellitus; therefore, women with diabetes should be encouraged to use other forms of contraception. However this effect in women under age 35 who are otherwise healthy is probably very low with little dose oral contraception, and reliable protection against pregnancy is a benefit for these patients that outweighs the little risk.