Smelling a gas leak while pregnant

What does the evidence say about smelling a natural gas leak during pregnancy?

1. Mercaptans are sulfur-containing odorant compounds intentionally added to natural gas, propane, and other fuel gases specifically to give an otherwise colorless, odorless gas a detectable smell for safety purposes. 1
2. Carbon monoxide is specifically dangerous because it's colorless, odorless, tasteless, and nonirritating, meaning exposure can happen unnoticed, unlike a gas leak that announces itself with the added mercaptan smell; common carbon monoxide sources include malfunctioning furnaces, gas stoves, and blocked chimneys or vents. 2
3. A scoping review of documented community gas-odorant exposure events found the most common symptoms were headache, eye and throat irritation, and respiratory complaints like coughing, generally transient rather than causing lasting harm at the exposure levels studied. 3
4. The human nose can detect mercaptan odorants at extremely low concentrations, often below 0.1 parts per billion, meaning you'll typically smell a leak long before the odorant itself reaches a concentration of real toxicological concern. 3
5. Carbon monoxide, a separate and more dangerous risk that can result from gas appliances not burning fuel completely, is colorless, odorless, and tasteless, causes symptoms including headache, nausea, and dizziness, and has been linked to a higher chance of miscarriage and effects on fetal brain development, which is why any suspected gas problem, not just the smell itself, warrants leaving the home and getting it checked. 4

Is smelling a natural gas leak safe in each trimester?

• First trimester. There's no trimester-specific data on mercaptan odorant exposure. The universal advice applies from the start: leave immediately, don't use light switches or flames, and call from outside.
• Second trimester. Same guidance continues. If you have ongoing symptoms like headache or nausea that started around when you first noticed a gas smell, mention the timing to your provider.
• Third trimester. Same guidance continues. A working carbon monoxide detector is a separate, worthwhile safeguard alongside gas-leak awareness, since CO is a distinct and more dangerous risk from any appliance burning gas incompletely.