Background:  Opiate and amphetamine use during pregnancy is frequently associated with cigarette smoking. The negative effects on fetal growth from nicotine combined with opiates or amphetamines during pregnancy are not well documented.
Aims:  To investigate the relationship between maternal opiate or amphetamine use and smoking on fetal growth.
Methods:  A retrospective study was performed comparing pregnancies affected with either opiates or amphetamines with individually matched controls. All mothers smoked cigarettes during pregnancy. The outcome measures included changes in fetal abdominal circumference, head circumference and femur length during the second half of pregnancy and weight, length and head circumference at birth.
Results:  There were 91 opiate‐ and 37 amphetamine‐affected pregnancies. Deviations from normative data only became apparent from the third trimester. The proportion of infants with a gestation‐adjusted birthweight below the 10th percentile was not significantly different in the opiate group compared to their controls 35 (38%). However, there was a significant difference in proportions in the amphetamine group and their controls (P < 0.001). We then compared antenatal growth patterns between the amphetamine group and their controls. Amphetamine‐exposed fetuses showed comparable growth parameters in the second trimester but significantly larger head and abdominal circumferences and longer femoral lengths in the third trimester than their respective controls (P < 0.05 for all). Conclusions:  When combined with cigarette smoking, opiates had no observed independent effect on birth parameters. Unexpectedly, in the amphetamine group, the negative effects of smoking on growth were altered in late pregnancy.