Carbon monoxide exposure during pregnancy

What does the evidence say about carbon monoxide exposure during pregnancy?

1. Mild carbon monoxide poisoning causes headache, nausea, vomiting, muscle weakness, and dizziness, while severe poisoning can bring confusion, chest pain, and loss of consciousness. 1
2. Carbon monoxide does not reach the fetus right away, but once it does, fetal blood carbon monoxide levels run higher than the mother's and clear up to five times more slowly. 2
3. Reported mortality from acute carbon monoxide poisoning in pregnancy runs high in the case literature, around 19 to 24 percent for the mother and 36 to 67 percent for the fetus, which is why any suspected exposure needs immediate emergency care. 2
4. In a review of 27 pregnancies with carbon monoxide poisoning managed with hyperbaric oxygen therapy, 24 infants (about 89 percent) were born healthy at full term, and none showed a developmental condition at a follow-up visit averaging around three years old. 3
5. The basic safety steps are installing a working carbon monoxide detector, keeping fuel-burning appliances properly vented, running generators outdoors only, and never letting a car idle in an attached garage. 4

Is carbon monoxide exposure safe in each trimester?

• First trimester. A baby's brain and organs are forming fastest in these weeks, which is part of why early carbon monoxide exposure has been flagged as a possible factor in later learning or behavior differences.
• Second trimester. The fetus clears carbon monoxide far more slowly than you do at any stage, so the same urgency around detectors and immediate emergency care applies through the middle of pregnancy too.
• Third trimester. A case report of carbon monoxide exposure at 31 weeks led to a newborn needing brain-imaging follow-up, which is why late-pregnancy exposure still calls for the same emergency response as earlier on, not a wait-and-see approach.