Chorevia

Day 245 of 280 · 35 weeks

The swab

Last reviewed · 3 min read · 9 sources · Plain-text version

Thirty-five weeks. Sometime in the next two weeks you'll be offered a quick swab for group B strep. Today you learn what a positive result does and doesn't mean.

Size this week
about the size of a honeydew melon
Length this week
around 46.2 cm from head to heel
A woman with a full bump in a striped t-shirt sitting on an exam-room chair, chatting with a smiling midwife who holds a clipboard, soft daylight, no equipment in focus.

Thirty-five weeks. One of the last routine tests of pregnancy is coming up, and it's one of the simplest: a swab. It helps to know what it's for before the result arrives.

Your baby

A single honeydew melon on a plain pale wooden table, soft window light.

Around now your baby is around 46.2cm long from head to heel, about the size of a honeydew melon (NHS). They're getting chubbier, and that fat will help them stay at the right temperature once they're born (NHS).

Your body

Group B strep (GBS) is a common bacterium. The NHS says up to 2 in 5 people carry it, and that most GBS infections in newborns are preventable (NHS). The AAP's figure for the US is about 1 in 4 women, usually without any symptoms or harm to themselves (AAP). It lives in the intestines and vagina and isn't spread through sex (MedlinePlus).

Most babies exposed during birth don't get sick, but a few develop serious illness (MedlinePlus). That's why you're tested: a swab of the outer vagina and rectum between 35 and 37 weeks, with results often back in a few days (MedlinePlus). The AAP and the Office on Women's Health put it at 36 to 37 weeks (AAP; OWH). The test has no risks (AAP).

Try today

  1. The GBS swab explainer

    Time: 10 minutes

    1. Ask at your next visit which week your swab will be, and write it down.

    2. Under it, write: "Positive means carrier, not infection." A positive result means the bacteria are present; it isn't an infection or an STD (AAP).

    3. Add what happens if it's positive: antibiotics through an IV during labor (MedlinePlus).

    4. Add: "Tell labor and delivery when I check in." The Office on Women's Health says to tell the staff (OWH).

    Make it work:

    If a C-section or an early labor is possible for you, the AAP says to make a GBS plan before 35 weeks (AAP). That's now: call and ask.

Watch for

  • Normal

    more vaginal discharge in the last weeks (NHS).

    Call your provider

    if it smells bad, looks greenish, itches, or hurts; vaginal infections matter in pregnancy because they may cause preterm labor (MedlinePlus).

  • Normal

    a little urine leaking when you laugh or cough (NHS).

    Call your provider right away

    if you might be leaking amniotic fluid (MedlinePlus). Waters breaking before 37 weeks is one of the things that raises the chance of passing on GBS (MedlinePlus).

  • Normal

    short, irregular tightenings that don't hurt (MedlinePlus).

    Call your provider right away

    for regular, painful contractions 5 to 10 minutes apart, or contractions lasting 60 to 90 seconds (MedlinePlus).

For you

A positive result can land like a judgment. It isn't one. GBS isn't spread through sex (MedlinePlus). It's a common bacterium that a lot of healthy people carry, and the swab simply tells your team whether to plan for antibiotics in labor.

If you're the partner: learn the one line, "positive means carrier, not infection." You may be the one repeating it at check-in.

Sources

This guide is general education that summarizes published research and guidance from groups like the American Academy of Pediatrics, the CDC, and the WHO. It isn’t medical advice, and every child develops on their own timeline. Your pediatrician knows your child; if something feels wrong, call them. In an emergency, call 911.

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