Carbon Monoxide


The information provided below is for readers based in the United States of America. Readers outside of the United States of America should seek the information from local sources.

What is carbon monoxide?

Carbon monoxide (CO) is an odorless, colorless gas that is created as a result of the incomplete combustion of carbon-based products, such as coal or gas. Each molecule of CO consists of one atom of carbon bound with one atom of oxygen. This molecular arrangement causes CO to take the place of molecular oxygen (O2) in binding to the hemoglobin (Hb) molecules of red blood cells (RBCs), and also to similar molecules, such as myoglobin (which stores O2 in muscle cells), neuroglobin (which stores O2 in nervous tissue), and certain “heme” molecules which are vital to the generation of energy inside mitochondria, the powerplant organelles within body cells. In other words, carbon monoxide replaces oxygen in the body. Because CO sticks much more tightly than O2 to all these molecules and prevents O2 from doing its job in the body, CO acts as a poison. CO poisoning, also called toxicity, usually comes from a single large exposure to CO, which can happen during pregnancy, and to people who are not pregnant. When pregnant, however, you are more susceptible to the effects of CO exposure.

Some sources of CO include: unvented kerosene and gas space heaters; leaking chimneys and furnaces; back-drafting from furnaces, gas water heaters, woodstoves, and fireplaces; gas stoves; generators and other gasoline powered equipment; automobile exhaust from attached garages; and tobacco smoke.

CO poisoning causes a variety of symptoms, such as headache, dizziness, nausea and vomiting, fatigue, confusion, changes in the level of consciousness, breathing difficulties, movement difficulties, and loss of consciousness. Since these symptoms are not specific to CO poisoning, the key to recognizing that a person may be suffering from this condition is realize potential exposure, such as from the burning of a substance indoors. CO poisoning can kill quickly if not recognized and treated with hyperbaric oxygen therapy (HBO2) if the poisoning is severe, or with normobaric oxygen therapy (100 percent O2 at normal pressure) if the poisoning is mild.

Is there a safe amount of carbon monoxide to which I can be exposed during pregnancy?

For most people, the presence of CO in the air at a concentration of 70 parts per million (ppm), or less, is not thought to be dangerous. For people with certain heart conditions, and possibly pregnant women, some symptoms may develop if they are exposed to air with CO levels somewhat lower than 70 ppm. Carbon monoxide detectors will go off and an alarm will sound after three and a half hours of continuous exposure at a level of 50 ppm, or will sound after eight minutes of continuous exposure at a level of 400 ppm – that's because a sudden exposure of 400 ppm is more dangerous than a longer exposure at a lower level.

Can exposure to carbon monoxide make it harder for me to get pregnant?

Possibly. CO is one of several agents present in tobacco smoke that has been implicated as a reason why tobacco smoking decreases fertility of both female and males who smoke. In such cases, the condition is called chronic CO poisoning, meaning a gradual poisoning from CO that harms the body over a long period without killing the person quickly as happens in cases of rapid exposure to CO, called acute CO poisoning.

Can carbon monoxide cause a miscarriage?

It is suspected that CO poisoning can cause a miscarriage, based on research related to tobacco as a miscarriage risk factor and on research in pigs.

Can carbon monoxide poisoning during my pregnancy cause a birth defect?

CO poisoning in the mother has been reported to cause problems with the baby’s brain, such as cerebral palsy, as well as stillbirth.

Are there long-term consequences to my baby from carbon monoxide exposure?

As noted above, CO poisoning in the mother has been reported to cause problems with the baby’s brain, such as cerebral palsy, as well as stillbirth.

I just found out I am 6 weeks pregnant and last weekend I was exposed to carbon monoxide. Will my baby have a problem?

If you were in a place in which CO levels in the air were high, but you just found out as you did not suffer any, or only minor symptoms, so long as you are now removed from the source of the CO, there is no concern that your baby will have a problem.

Is high exposure to carbon monoxide on only some days of the week as risky as being exposed to carbon monoxide everyday but at lower amounts?

A single high exposure to CO is riskier than more frequent exposure to lower amounts of CO. The latter situation is chronic CO poisoning as occurs with tobacco poisoning and is not good for you, but high exposure can be quickly fatal.

Is it ok to breathe some carbon monoxide after the first trimester?

No. CO is a poison and is bad for you and your baby at any point in the pregnancy.

How will I know if carbon monoxide has hurt my baby?

If you suffered CO poisoning during pregnancy, and the Apagar score of the newborn is low and cannot be attributed to some other problem, this could mean that the CO damaged the baby, in which case testing will be performed.

Is there any hope for a baby who has been exposed to carbon monoxide throughout pregnancy?

If the exposure to CO is throughout pregnancy, this describes a situation of chronic CO poisoning in the mother. In some cases, the baby will be fine, whereas in other cases there can be problems, particularly with the brain.

Can I be exposed to carbon monoxide while breastfeeding?

Exposure to CO is almost always accidental and it’s bad for you whether you are breast feeding or not. CO poisoning does make breast milk dangerous for the baby, but if you have acute CO poisoning you won’t be in a position to breastfeed.

What if the father is exposed to carbon monoxide prior to conception?

CO is one of several agents present in tobacco smoke that has been implicated as a reason why tobacco smoking decreases fertility in males who smoke. In such cases, the condition is called chronic CO poisoning.

Resources for carbon monoxide poisoning during pregnancy:

For more information about carbon monoxide during pregnancy, contact (800-994-9662 [TDD: 888-220-5446]) or read the following articles:

Mayo Clinic: Carbon Monoxide Poisoning

US Centers for Disease Control and Prevention: Carbon Monoxide: Frequently Asked Questions

United States Consumer Product Safety Commission:  Carbon Monoxide

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General information

It is very common for women to worry about having a miscarriage or giving birth to a child with a birth defect while they are pregnant. Many decisions that women make about their health during pregnancy are made with these concerns in mind.

For many women these concerns are very real. As many as 1 in 5 pregnancies end in a miscarriage, and 1 in 33 babies are born with a birth defect. These rates are considered the background population risk, which means they do not take into consideration anything about the health of the mom, the medications she is taking, or the family history of the mom or the baby’s dad. A number of different things can increase these risks, including taking certain medications during pregnancy.

It is known that most medications, including over-the-counter medications, taken during pregnancy do get passed on to the baby. Fortunately, most medicines are not harmful to the baby and can be safely taken during pregnancy. But there are some that are known to be harmful to a baby’s normal development and growth, especially when they are taken during certain times of the pregnancy. Because of this, it is important to talk with your doctor or midwife about any medications you are taking, ideally before you even try to get pregnant.

If a doctor other than the one caring for your pregnancy recommends that you start a new medicine while you are pregnant, it is important that you let them know you are pregnant.

If you do need to take a new medication while pregnant, it is important to discuss the possible risks the medicine may pose on your pregnancy with your doctor or midwife. They can help you understand the benefits and the risks of taking the medicine.

Ultimately, the decision to start, stop, or change medications during pregnancy is up to you to make, along with input from your doctor or midwife. If you do take medications during pregnancy, be sure to keep track of all the medications you are taking.

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