620: Effect of opioid maintenance therapy on placental efficiency

Methadone (MET) and subutex (SUB) are used in medication assisted treatment (MAT) during pregnancy and cross the placenta. Infants exposed to MAT in utero are at risk for intrauterine growth restriction, but little is known about placental function. Placental efficiency (PE, birthweight in grams/ placental weight in grams) is lower in obstetrical complications affecting growth, including pre-eclampsia. We hypothesize that exposure to MAT is associated with lower placental efficiency. 64 patients treated with MET and 21 on SUB were included. A cohort of 565 women not exposed to opioids (non-MAT) was used as a comparison group. The association between placental efficiency and maternal characteristics was evaluated using a multiple linear regression model that included gestational age, maternal pre-pregnancy BMI, MAT program, race, and active cigarette smoking as covariates. One way ANOVA was performed in actively smoking Caucasian women at term, to assess differences between groups. In the regression model, PE was associated with gestational age, maternal pre-pregnancy BMI, Caucasian race, and maternal smoking. Thus, to assess PE differences between MAT groups, only term, Caucasians who smoked were analyzed. Placental weight (p=0.03) and birthweight (p=0.008) were significantly different between groups. MET treatment was associated with a larger placenta and smaller baby. Birthweight was also smaller in the SUB group. PE was decreased in the MET, but not SUB group as compared to non-MAT controls (p<0.005; Figure 1). MAT is associated with changes in placental efficiency, compared to women not exposed to MAT. Methadone treatment is associated with larger placentas, yet smaller babies, suggesting reduced placental function, confirmed by a lower placental efficiency. Alternatively, treatment with SUB lead to relatively efficient placentas, as compared to non-MAT controls. The association between MET treatment and decreased PE may support the preferred use of SUB in pregnancy.