The fetus is uniquely susceptible to carbon monoxide (CO) exposure. We present a case of severe unintentional CO poisoning in the first trimester of pregnancy. A 23-year-old G5P2022 female at 11 weeks’ gestational age sat in a car with the engine idling. She was unaware that the vehicle’s exhaust pipe was blocked with snow. She was found to be unresponsive, with an initial carboxyhemoglobin (COHb) concentration of 47.1%. She underwent emergent treatment with hyperbaric oxygen therapy. The remainder of her pregnancy was complicated by a diagnosis of myasthenia gravis. She delivered a full-term infant who was noted to have persistently small head circumference. Fetal hemoglobin binds to CO more tightly than adult hemoglobin, and fetal carboxyhemoglobin concentrations are reported to exceed maternal levels. Fetal abnormalities may occur after CO poisoning in pregnancy and vary based on the gestational age of the fetus at the time of the exposure as well the chronicity of the exposure. Fetal survival after maternal CO exposure is possible even with significantly elevated maternal COHb concentrations, although teratogenic effects may occur depending on the timing of exposure.

Nowadly, Johnson-Arbor, Boyle (2018). Severe unintentional first trimester carbon monoxide poisoning: case report. Undersea & hyperbaric medicine : journal of the Undersea and Hyperbaric Medical Society, Inc, ;45(4):453-456. https://www.ncbi.nlm.nih.gov/pubmed/30241125