The purpose of this study was to examine the relationship between the level of maternal serum coenzyme Q10 (CoQ10), which is a lipid-soluble antioxidant, maternal body weight gain, fat mass gain, and infant birth weight. A longitudinal observational study was conducted with 50 healthy pregnant women (average age: 31.1 years, average body mass index (BMI): 21.3 kg/m2 at prepregnancy) at each trimester. CoQ10 levels were measured by high performance liquid chromatography. Maternal weight and body composition were measured by a bioelectrical impedance analysis. The CoQ10 levels significantly increased throughout pregnancy from the first trimester to the third trimester (P < 0.001), and correlated with not only the serum cholesterol levels (P < 0.01) but also with the serum acetoacetic acid levels (P < 0.05) in the third trimester. The CoQ10 levels correlated with the maternal weight gain (P < 0.05) and fat mass gain (P < 0.05) from the second to the third trimester, after adjusting for lipid markers, age, and smoking habits. The level of CoQ10 during the third trimester was also significantly associated with the infant birth weight (P < 0.05) after adjusting for gestational age, maternal prepregnancy BMI, and smoking habits. Therefore, it is concluded that the level of maternal CoQ10 is positively associated with fetal growth, balancing rapid metabolic changes in the last half of a normal pregnancy.