Maternal exposure to tobacco and alcohol is a known cause, among others, for fetal growth restriction (FGR). Clinically, FGR can be subclassified into two forms: intrauterine growth restriction (IUGR) and small for gestational age (SGA), based on the severity of the growth retardation, and abnormal uterine artery Doppler or cerebro-placental ratio. This study aimed at investigating any differential correlation between maternal exposures to these toxins with the two clinical forms of FGR. Therefore, a case-control study was conducted in Barcelona, Spain. Sixty-four FGR subjects, who were further subclassified into IUGR (n = 36) and SGA (n = 28), and 89 subjects matched appropriate-for-gestational age (AGA), were included. The levels of nicotine (NIC) and ethyl glucuronide (EtG), biomarkers of tobacco and alcohol exposure, respectively, were assessed in the maternal hair in the third trimester. Our analysis showed 65% of the pregnant women consumed alcohol, 25% smoked, and 19% did both. The odds ratios (ORs) of IUGR were 21 times versus 14 times for being SGA with maternal heavy smoking, while with alcohol consumption the ORs for IUGR were 22 times versus 37 times for the SGA group. The differential correlations between these toxins with the two subtypes of FGR suggest different mechanisms influencing fetal weight. Our alarming data of alcohol consumption during pregnancy should be considered for further confirmation among Spanish women.