Oxycodone does not affect placental circulatory physiology during the early first stage of labor—A randomized trial

INTRODUCTION: Opioids are used for pain relief during the first stage of labor. Oxycodone can cause maternal hypotension that may modify utero‐ and fetoplacental circulatory physiology. We hypothesized that maternal intravenous (i.v.) oxycodone has no detrimental effect on utero‐ and fetoplacental hemodynamics during the early first stage of labor. MATERIAL AND METHODS: Twenty‐two parturients requiring pain relief during the first stage of labor were randomized in a double‐blinded and placebo‐controlled study. By Doppler ultrasonography, both uterine artery (Ut) and umbilical vein (UV) volume blood flows (Q), Ut pulsatility index (PI), and Ut vascular resistance (RUt) were calculated. Blood flow velocity waveforms were obtained between uterine contractions. After baseline measurements, women received oxycodone 0.05 mg/kg or a placebo intravenous. Doppler ultrasonography was repeated up to 120 min after the first drug administration. The second dose of oxycodone 0.05 mg/kg was allowed at 60 min to all parturients with contraction pain ≥5/10. Maternal plasma samples were collected at each study phase and after delivery with umbilical cord plasma samples, to measure oxycodone concentrations. ClinicalTrials.gov identifier (NCT no. NCT02573831). RESULTS: At baseline, mean QUt and QUV did not differ significantly between the placebo‐first (478 mL/min and 57 mL/min/kg) and the oxycodone‐first (561 mL/min and 71 mL/min/kg) groups. In addition, RUt and Ut PI were comparable between the groups. Following oxycodone at 60 min, mean QUt and QUV (714 mL/min and 52 mL/min/kg) were similar to the placebo‐first (520 mL/min and 55 mL/min/kg) group. Furthermore, all the measured parameters were comparable to the baseline values. At 60 min after the first study drug administration, all the parturients in the placebo‐first group needed intravenous oxycodone 0.05 mg/kg. At 120 min, we found no statistically significant change in any of the measured parameters. No significant correlation was found between maternal oxycodone concentration and QUt or QUV. Furthermore, newborn oxycodone concentration did not correlate with QUV. CONCLUSIONS: Oxycodone did not have any detrimental effect on either utero‐ or fetoplacental circulatory physiology during the early first stage of labor. Maternal plasma oxycodone did not correlate with utero‐ and fetoplacental hemodynamics. No correlation was found between newborn oxycodone concentration and fetoplacental hemodynamics.