How to tell the difference between…

[Drizzlesfr]

Hydrogen sulfide and open drain/sewer smell?!

We have an intermittent eggy smell in the house and I’m getting concerned it’s something awful.

Hydrogen sulfide IS the gas that comes from sewers and causes the unpleasant smell.

If you're smelling open drain/sewer smell, that is hydrogen sulfide. It's what causes that smell in plumbing; it's just usually in very small quantities along with ammonia, methane, CO2. A very, VERY small amount of it still creates a powerful odor.

Unless you live next door to a tannery or a waste treatment plant the culprit is pretty unlikely to be pure H2S and your house isn't considered a "confined space" for it to be dangerous. It is super unpleasant though so maybe call a plumber to inspect? It tends to happen when a drain is cracked or clogged, or there's buildup in the pipes.

Ok got it thanks. Is it harmful to health? I’m worried as I’m pregnant and it’s been like this throughout.

It's harmful in concentrations much larger than "drain smell". We can start smelling it at around one hundredth of one part per million. It takes a concentration of roughly 200x that to cause mild health impacts like watery eyes, coughing, etc.

Pregnancy heightens the sense of smell -- probably worth getting your plumbing looked at, just for your own comfort!