Background: It has been reported that carbohydrate metabolism does not deteriorate in pregnancy in the African, an observation at variance with general teaching. Objective: To determine the effect of pregnancy on medium term carbohydrate metabolism Methods: Medium term carbohydrate metabolism was evaluated in pregnant and non-pregnant Nigerian women using changes in Glycoted Plasma Proteins (GPP) as a surrogate for medium-term carbohydrate metabolism. Study subjects included women in all three trimesters of pregnancy, a group of non-pregnant women with normal carbohydrate metabolism and another group of women with confirmed diabetes already on treatment but not pregnant . Fasting plasma glucose was determined by the glucose oxidase method while GPP was determined using a modification of the thiobarbituric method with correction for levels of total plasma proteins (TPP). Average values are presented as mean (SD) while relationship between variables were determined using Pearson product moment correlation coefficients. Significance of p values of determinations is set at p <0.05. Results: Women in the various pregnancy trimesters were similar in age and without family or personal history of diabetes mellitus. Fasting plasma glucose (FPG) levels of pregnant women in all trimesters were lower than those of non-pregnant women of similar age. GPP values in the first and second trimesters were lower than non-pregnant women and third trimester pregnant women. GPP was highest in the third trimester of pregnancy even being significantly higher than in the non-pregnant women. Correlation between FPG and GPP was highest and significant in the third semester. Conclusion: FPG levels are poor reflections of the carbohydrate tolerance in pregnancy. Carbohydrate metabolism is enhanced in the first trimester and thereafter deteriorates throughout pregnancy. When using GPP to assess carbohydrate metabolism in pregnancy, correction should be made for the level of total plasma proteins. Carbohydrate metabolism in the African deteriorates with advancing pregnancy.