Aim: To investigate the difference in fetal heart rate of opioid-dependent mothers compared to non-dependent mothers in the first trimester of pregnancy.
Design: The data of 74 consecutive singleton pregnancies of mothers enrolled in a maintenance programme for opioid-dependent women was matched to 74 non-exposed singleton pregnancies by maternal age, crown-rump length, smoking status, ethnic background and mode of conception.
Measurement: Fetal heart rate measured as part of first-trimester screening by Doppler ultrasound between 11+0 and 13+6 gestational weeks was compared retrospectively.
Findings: The mean fetal heart rate in opioid-dependent mothers was 156.0 beats per minute (standard deviation 7.3) compared to 159.6 (6.5) in controls. The difference in fetal heart rate was significant (P = 0.02). There was a significant difference in mean maternal body mass index (P = 0.01) but not in mean nuchal translucency (P = 0.3), gestational age (0.5), fetal gender (P = 0.3) and parity (P = 0.3) between both groups. Fifty-five per cent (41 of 74) of cases were taking methadone, 30% (22 of 74) buprenorphine and 15% (11 of 74) were taking slow-release morphines throughout the pregnancy.
Conclusions: In fetuses of opioid-dependent mothers a decreased fetal heart rate can already be observed between 11+0 and 13+6 gestational weeks. The effect of opioid intake needs to be taken into consideration when interpreting fetal heart rate in opioid-dependent mothers at first-trimester screening.