Impact of anaesthetics and analgesics on fetal growth in the mouse

Common anaesthetic and analgesic agents used during pregnancy in mice have been observed to cause fetal growth restriction. We investigated the impact of therapeutic doses of three anaesthetics (ketamine/xylazine, isoflurane, and tribromoethanol) and two analgesics (buprenorphine and meloxicam) on fetal and placental growth. Pregnant mice were treated with one of these agents at fertilization (E0), attachment (E4), beginning of organogenesis (E6), end of organogenesis (E12), or during the logarithmic growth phase (E15), or they were placed into an untreated control group. At term (E18), fetal and placental growth were evaluated, morphological analyses were performed, and skeletal measurements were conducted. Fetal growth was reduced significantly (P < 0.01) by ketamine/xylazine treatment at E0, E4, E12, or E15, by isoflurane administered at E0 or E6, and by tribromoethanol administered at E6 or E12. Two-day treatment with buprenorphine beginning at E4 or E6, or with meloxicam at E0 also significantly reduced fetal growth (P<0.01). Neither placental growth nor litter size was significantly affected by any of these agents. The occurrence of microphthalmia was nearly eight-fold higher (P<0.05) in response to buprenorphine administration at E6 compared with controls. The length of the humerus was reduced at most gestation times in response to each of these agents and was correlated (P<0.01) with fetal weight for ketamine/xylazine, tribromoethanol, and meloxicam. These data reveal patterns of acceptable and detrimental anaesthetic and analgesic use during fetal development and have refined our capability to provide recommendations for the use of these agents during pregnancy in the mouse.