Group B strep positive: what it actually means

What GBS is

A common bacterium that lives harmlessly in the gut and vagina of roughly a quarter of pregnant people. It is not a sexually transmitted infection, not a sign of poor hygiene, and not something you caught. Most carriers have no symptoms and would never know without the swab.

It matters only because a baby can pick it up during birth, and in a small number of cases that causes serious early infection. The screening-and-antibiotics approach exists because it substantially reduces those cases.

Why the timing of the test

Screening happens between 36 0/7 and 37 6/7 weeks — a deliberately narrow window, because carriage fluctuates. A swab at 28 weeks wouldn't reliably predict your status at delivery, so testing close to birth is what makes the result actionable. It's a quick vaginal and rectal swab, sometimes one you can take yourself.

What happens in labor

IV antibiotics, usually penicillin, given during labor and repeated at intervals until birth. The target is at least four hours of antibiotics before delivery, which is why you'll be told to come in promptly rather than laboring at home for a long stretch.

Tell them you're GBS positive at the first call. If you have a penicillin allergy, make sure it's on record well before labor — the alternative antibiotic sometimes depends on additional lab testing that's better done in advance.

What it doesn't mean

It doesn't mean a cesarean, and a planned cesarean without labor or ruptured membranes usually doesn't need the antibiotics at all. It doesn't usually rule out a water birth or midwife-led care, though it does mean a cannula. And it doesn't carry over automatically to a future pregnancy — you'd be swabbed again, since carriage changes.