Introduction Low birth weight is associated with an increased risk of heart disease, high blood pressure and diabetes in adult life. Fetal growth is determined by nutrient availability, which is related to placenta nutrient transport. Medium chain fatty acids (MCFAs) are a particular class of nutrients, known to be a readily available energy source. Until now no data are reported on these MCFAs in low birth weight fetus. Aim This is a prospective study conducted in a tertiary center of prenatal diagnosis to investigate the maternal and fetal MCFAs levels in appropriate for gestational age (AGA), intrauterine growth restricted (IUGR), and small for gestational age (SGA) pregnancies. Method The plasmatic levels of MCFAs in AGA, IUGR and SGA mother-infant pairs were quantified by gas chromatography-mass spectrometry. The analytical method had a linearity range of 0.1-50 mg/L and a limit of quantification of 0.03 mg/L. Reduced fetal growth was defined as an estimated fetal weight below the 3rd-10th percentile for gestational age, with (IUGR) or without (SGA) fetal Doppler abnormalities. Result Maternal and fetal MCFAs plasma levels were significantly different among SGA, IUGR and AGA groups. Additionally, the observed MCFAs fetal to maternal ratio is >1 for IUGR group, whilst for SGA and AGA the fetal to maternal ratio is less than one. Conclusion Changes in MCFAs levels in fetal and maternal plasma are not related to placental functionality or nutrients availability, suggesting the presence of a de novo biosynthesis.