Effect of Acetaminophen on Fetal Activity

The aim of this study is to determine if maternal administration of acetaminophen affects fetal activity and thereby the interpretation of clinical assessments of fetal well being.

A longitudinal study was performed in 20 women between 30 and 34 weeks' gestation with uncomplicated pregnancies. A 1-hour ultrasound was performed and recorded to document baseline fetal breathing and body movements. All the subjects were then given a 1,000 mg dose of oral acetaminophen. One hour later, a second 1 hour ultrasound was performed to document postacetaminophen fetal breathing and body movements. The number of episodes and total duration of gross body and fetal breathing movements were then assessed by a blinded observer. The pre- and post-acetaminophen values were compared using a repeated measures t-test.

There was no significant effect of acetaminophen on the number of episodes or time spent in fetal breathing or body movements when each activity parameter was analyzed separately. In addition, there was no effect when fetal breathing and body movements were combined into a single composite activity score.

Although acetaminophen has been shown to affect fetal activity in animal models, it has little effect on humans. Thus, maternal administration of acetaminophen should not affect assessment of fetal well being.