In utero effects of opioids on fetal growth

Studies indicate antenatal opioid use is associated with birth size deficits, as evidenced by reductions in birth weight and head circumference. However, there remains a limited understanding of how early this growth restriction occurs, and what specific parameters are affected. This novel study evaluated global and specific growth deficits associated with prenatal opioid exposure between 18-22 weeks' gestation as assessed during anatomy ultrasounds.

Pregnant women who completed an anatomy ultrasound were identified via electronic medical records from a large academic obstetric practice. The study group used opioids, with tobacco and/or marijuana use permitted (n = 41). The control group could have used tobacco and/or marijuana, but not opioids (n = 308). Neither group had alcohol or other drug exposure. Records were reviewed for medical history and ultrasound size parameters, coded as percentiles for gestational age.

Demographics and medical histories were compared with several significant differences noted. After controlling for these differences, significant (p < 0.05) growth deficits were identified in opioid-exposed fetuses. Specifically, reductions >10 percentile points were observed in head circumference, biparietal diameter, and humerus length for opioid-exposed fetuses compared to controls. Additionally, intrauterine growth restriction (IUGR) was diagnosed five times more often. Femur length was significantly reduced in opioid-exposed fetuses prior to adjustment for confounding (p = .016), but this reduction was not significant (p = .072) after controlling for background differences. Estimated fetal weight (p = .274) and abdominal circumference (p = .633) were not significantly different between exposure groups.

Fetal opioid exposure predicted various bone growth deficits during routine anatomy ultrasound, indicating the effects of opioid exposure on size deficits may be evident as early as 18-22 weeks' gestation. These findings may also suggest that in utero opioid exposure negatively impacts bone growth specifically rather than weight or fat/muscle mass. Additional studies with larger sample sizes may also reveal significantly reduced femur length, further supporting a negative impact on bone growth. Future studies evaluating bone health and immune function in children after antenatal opioid exposure may help clarify this specific effect of opioids on bone development.