Carbon Monoxide
Everyday exposureHome & environmentAlso called · 8 names▾▴
CO, carbon monoxide poisoning, CO leak, carbon monoxide exposure, furnace fumes, generator fumes, car exhaust, CO poisoning
Household gas exposure
General information · effects depend on amount, timing, and how it is used. About these sources
Research strength: 3 / 5
MotherToBaby says carbon monoxide poisoning reduces the oxygen carried to organs and that fetal carbon monoxide may take longer to clear. UKHSA reports fetal or newborn death and neurological effects after high exposure, usually when the pregnant person has moderate or severe illness. In a small prospective study, 3 of 5 severe poisoning cases had adverse outcomes, including two stillbirths and one case of cerebral palsy; 31 mild or moderate cases had normal reported development. This study cannot estimate an individual's risk, and evidence does not give a separate first-trimester outcome estimate. CDC says hyperbaric oxygen is the treatment of choice for pregnant patients with poisoning, even if they are less severely poisoned. Ask your provider about your situation.
Last reviewed: 2026-10-16
Sources
- MotherToBaby: Carbon MonoxideTeratology service
- UKHSA: Carbon monoxide toxicological overviewUK government
- Koren et al., prospective multicenter study of pregnancy outcomes after accidental CO poisoningUS government
- CDC: Clinical Guidance for Carbon Monoxide Poisoning Following Disasters and Severe WeatherUS government
Research strength: 3 / 5
MotherToBaby says exposure timing and amount may matter, but does not give a second-trimester risk estimate. A 2025 Oxford retrospective cohort of 5,041 pregnancies with recorded breath CO found that readings above 2 ppm were associated with lower birth weight and higher odds of small-for-gestational-age birth and preterm birth. In the high-CO nonsmoker group, increased risks were not statistically significant, and the study cannot show that CO alone caused the outcomes. UKHSA's 2026 antenatal algorithm uses breath readings to guide screening and follow-up, not to estimate trimester-specific outcomes. CDC says hyperbaric oxygen is the treatment of choice for pregnant patients with poisoning, even if they are less severely poisoned. Ask your provider about your situation.
Last reviewed: 2026-10-16
Sources
- MotherToBaby: Carbon MonoxideTeratology service
- Galka et al., Carbon monoxide levels, smoking and adverse pregnancy outcomesUS government
- UKHSA: Carbon monoxide antenatal checks algorithmUK government
- CDC: Clinical Guidance for Carbon Monoxide Poisoning Following Disasters and Severe WeatherUS government
Research strength: 3 / 5
MotherToBaby says exposure timing and amount may matter, but does not give a third-trimester risk estimate. UKHSA reports fetal or newborn death and neurological effects after high acute exposure, especially when maternal illness is moderate or severe. In a small prospective study, 3 of 5 severe poisoning cases had adverse outcomes, while 31 mild or moderate cases had normal reported development; the study is too small to predict an individual's outcome. A 2025 UK study monitored 161 selected households for carbon monoxide exposure but did not measure pregnancy outcomes. CDC says hyperbaric oxygen is the treatment of choice for pregnant patients with poisoning, even if they are less severely poisoned. Ask your provider about your situation.
Last reviewed: 2026-10-16
Sources
- MotherToBaby: Carbon MonoxideTeratology service
- UKHSA: Carbon monoxide toxicological overviewUK government
- Koren et al., prospective multicenter study of pregnancy outcomes after accidental CO poisoningUS government
- Place et al., Carbon monoxide exposure in pregnant women in the UKUS government
- CDC: Clinical Guidance for Carbon Monoxide Poisoning Following Disasters and Severe WeatherUS government
Carbon Monoxide — Breastfeeding
Research strength: 1 / 5
MotherToBaby says no human studies have examined carbon monoxide exposure during breastfeeding. The fact sheet advises discussing breastfeeding with a healthcare provider if poisoning occurs. CDC describes carbon monoxide poisoning as a medical emergency that can cause sudden illness and death. Available human evidence does not provide milk measurements or infant-outcome data after maternal poisoning. Ask your provider about your situation.
Last reviewed: 2026-10-16
Pregnancy
MotherToBaby states that effects may depend on exposure timing and amount, but does not provide trimester-specific risk estimates. UKHSA's 2022 overview reports fetal and newborn death and neurological effects after high acute exposure, generally with moderate or severe maternal illness. In Koren et al.'s 1991 prospective multicenter study, adverse outcomes occurred in 3 of 5 severe cases, including two stillbirths and one case of cerebral palsy; all 31 reported mild or moderate cases had normal physical and neurobehavioral development. This small uncontrolled study cannot estimate a personal risk or prove treatment effects. A 2025 Oxford retrospective cohort analyzed 5,041 pregnancies with recorded breath CO and reported lower mean birth weight and higher odds of small-for-gestational-age birth and preterm birth above 2 ppm; high-CO nonsmokers had increased risks that were not statistically significant. The study is observational, the exposures may be linked to smoking and other factors, and it does not establish that CO alone caused the outcomes. UKHSA's 2026 antenatal algorithm provides screening and follow-up actions, not trimester outcome estimates. CDC's 2026 clinical guidance says hyperbaric oxygen is the treatment of choice for pregnant patients with CO poisoning, even if they are less severely poisoned.
Breastfeeding
MotherToBaby reports that no human studies have examined carbon monoxide exposure during breastfeeding. Its sheet advises discussing breastfeeding with a healthcare provider if poisoning occurs. Targeted PubMed and LactMed searches did not identify a direct human study of maternal CO poisoning that measured carbon monoxide in milk or infant outcomes. The available information does not establish an infant outcome after maternal poisoning through milk.
Carbon monoxide is an odorless, colorless gas produced by incomplete burning of fuel. MotherToBaby says it enters the body by breathing it in. This entry describes environmental exposure, not a medication with a dose or formulation.
What was tested
The evidence includes case reports and reviews of acute poisoning, a small prospective multicenter study of pregnancy outcomes (Koren et al., 1991), a 2025 retrospective Oxford cohort using breath CO readings and birth outcomes, and a 2025 study measuring CO in 161 selected UK households without assessing pregnancy outcomes. A 1977 mathematical model and an experiment in sheep examined maternal and fetal CO uptake and elimination. The pregnancy outcome studies are observational and do not provide a reliable trimester-specific personal risk estimate. PubMed and LactMed searches did not identify a direct human study of maternal poisoning, milk levels, or infant outcomes during breastfeeding.
Why fetal carbon monoxide clears more slowly
- Source A says
- UKHSA's 2022 overview attributes the longer fetal elimination half-life partly to greater fetal hemoglobin binding affinity and a smaller diffusion gradient between maternal and fetal blood. (UKHSA: Carbon monoxide toxicological overview)
- Source B says
- The 2025 Polish Medical Society position statement notes that some data suggest fetal hemoglobin's CO affinity may be equal to or lower than adult hemoglobin under physiological conditions, while also describing slower fetal CO elimination. (Anand et al., Polish Medical Society Section of Clinical Toxicology position statement on acute CO poisoning)
- Why they differ
- The sources weigh different physiological conditions and kinetic evidence. The older UKHSA overview cites a higher-affinity mechanism, while the 2025 statement summarizes literature that questions whether that affinity difference holds under physiological conditions. Both describe slower fetal clearance; the precise mechanism is not settled.
- Other sources
- A 1977 mathematical model and a 1977 sheep experiment found fetal CO levels lagged during uptake and washout occurred more slowly than in the mother. (Hill et al., Carbon monoxide exchanges between the human fetus and mother: a mathematical model, Longo and Hill, Carbon monoxide uptake and elimination in fetal and maternal sheep)
- What the evidence shows overall
- Available model and animal evidence supports slower fetal uptake and washout, while whether fetal hemoglobin itself binds CO more tightly under physiological conditions remains unsettled. The entry describes slower fetal clearance without asserting one explanation.
- MotherToBaby lists regular maintenance of fuel-burning appliances and working carbon monoxide detectors as prevention measures. (MotherToBaby)
- CDC says generators, grills, camp stoves, and other fuel-burning devices should be used outdoors, away from homes and openings such as windows. (CDC)
- UKHSA's 2026 antenatal algorithm describes breath screening and follow-up steps for maternity staff when a pregnant person has a raised reading or possible exposure. (UK Health Security Agency)
- EPA lists ambient-air standards of 9 ppm averaged over 8 hours and 35 ppm over 1 hour. These are population air standards, not an individualized pregnancy cutoff. (US Environmental Protection Agency)
- NIOSH lists a recommended workplace time-weighted average of 35 ppm and a 200 ppm ceiling. These are occupational exposure limits, not pregnancy-specific personal thresholds. (NIOSH)
General research, not specific to pregnancy.
CDC describes carbon monoxide as an odorless, colorless gas that can cause sudden illness and death when inhaled. Its symptoms can include headache, dizziness, weakness, nausea, vomiting, chest pain, and confusion.
- CDC lists furnaces, portable generators, and charcoal grills among common sources of household carbon monoxide exposure. (CDC: Carbon Monoxide Poisoning Basics)
- The EPA ambient-air standards are 9 ppm over 8 hours and 35 ppm over 1 hour. (US EPA: National Ambient Air Quality Standards table)
- NIOSH's recommended workplace limit is a 35 ppm time-weighted average, with a 200 ppm ceiling. (NIOSH Pocket Guide: Carbon monoxide)
- MotherToBaby: Carbon MonoxideTeratology serviceSecondary
- UKHSA: Carbon monoxide toxicological overviewUK governmentSecondaryPage dated 2022-05-24Independent check
- UKHSA: Carbon monoxide antenatal checks algorithmUK governmentSecondaryPage dated 2026-06-08Independent check
- CDC: Clinical Guidance for Carbon Monoxide Poisoning Following Disasters and Severe WeatherUS governmentSecondaryPage dated 2026-08-21Independent check
- CDC: Carbon Monoxide Poisoning BasicsUS governmentSecondaryPage dated 2026-01-12
- Koren et al., A multicenter, prospective study of fetal outcome following accidental carbon monoxide poisoning in pregnancyUS governmentPrimaryIndependent check
- Galka et al., Carbon monoxide levels, smoking and adverse pregnancy outcomesUS governmentPrimaryIndependent check
- Place et al., Carbon monoxide exposure in pregnant women in the UKUS governmentPrimary
- Anand et al., Polish Medical Society Section of Clinical Toxicology position statement on acute CO poisoningUS governmentSecondaryIndependent check
- Hill et al., Carbon monoxide exchanges between the human fetus and mother: a mathematical modelUS governmentPrimaryIndependent check
- Longo and Hill, Carbon monoxide uptake and elimination in fetal and maternal sheepUS governmentPrimaryIndependent check
- US EPA: National Ambient Air Quality Standards tableSecondaryPage dated 2025-11-04
- NIOSH Pocket Guide: Carbon monoxideUS governmentSecondaryPage dated 2019-10-30
Last reviewed 2026-10-16
Independent check 2026-10-16
Not yet clinician-reviewed
Ask your provider about your situation.