# Day 249: The penicillin question

> Thirty-five weeks and four days. If you've ever been told you're allergic to penicillin, today is the day to ask whether that's still true, before labor.

- Series: Your eighth month of pregnancy, day by day (https://chorevia.com/learn/pregnancy-month-8), day 249 of 280, 35 weeks + 4 days
- Your baby this week: about the size of a honeydew melon; around 46.2 cm from head to heel
- Canonical URL: https://chorevia.com/learn/pregnancy-month-8/day-249
- Last reviewed: 2026-10-22
- Publisher: Chorevia (https://chorevia.com)
- Cite as: Chorevia. "Day 249: The penicillin question." Last reviewed October 22, 2026. https://chorevia.com/learn/pregnancy-month-8/day-249

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.

Thirty-five weeks and four days. A question that sounds like paperwork and matters more than it looks: does your chart say you're allergic to penicillin, and is it right?

## Your baby

Around now your baby is around 46.2cm long from head to heel, about the size of a honeydew melon ([NHS](https://www.nhs.uk/best-start-in-life/pregnancy/week-by-week-guide-to-pregnancy/3rd-trimester/week-35/)). MedlinePlus puts their weight at weeks 35 to 37 at about 5 1/2 pounds (2.5 kilograms) ([MedlinePlus](https://medlineplus.gov/ency/article/002398.htm)). Every week from here is mostly about filling out.

## Your body

If your group B strep (GBS) swab comes back positive, you'll get antibiotics through an IV during labor ([MedlinePlus](https://medlineplus.gov/ency/patientinstructions/000511.htm)). The AAP says they work best when given at least 4 hours before delivery, and that antibiotics taken before labor don't prevent passing GBS to the baby ([AAP](https://www.healthychildren.org/English/ages-stages/prenatal/Pages/Get-Tested-for-Group-B-Strep.aspx)). So the timing is labor itself, and the plan needs to be ready before then.

That's where allergies come in. Roughly nine in ten women who think they are allergic to penicillin are not truly allergic, the AAP says, and it recommends allergy testing ([AAP](https://www.healthychildren.org/English/ages-stages/prenatal/Pages/Get-Tested-for-Group-B-Strep.aspx)). Finding out now, rather than in labor, gives your team the full picture while there's still time to act on it.

## Try today

### The penicillin-allergy check

- **Time:** 15 minutes

1. Look at what your records say about penicillin, and write down what you remember: what happened, how old you were, who said it was an allergy.
2. If you think you're allergic, ask your provider this week whether testing makes sense for you, as the AAP recommends ([AAP](https://www.healthychildren.org/English/ages-stages/prenatal/Pages/Get-Tested-for-Group-B-Strep.aspx)).
3. Ask what your team would give in labor if you test GBS positive and the allergy stands.
4. Write the answer on the same page as your GBS swab date, so it's all in one place.

**Make it work:** No allergy history? Then this one's done in a minute. Use the time to check your swab date is booked.

## Watch for

- **Normal:** feeling completely well if you carry GBS; most carriers have no symptoms ([AAP](https://www.healthychildren.org/English/ages-stages/prenatal/Pages/Get-Tested-for-Group-B-Strep.aspx)). **Call your provider right away** if your waters break, and tell them the time and the color or smell ([OWH](https://womenshealth.gov/pregnancy/childbirth-and-beyond/labor-and-birth)); 18 or more hours after the waters break without delivery raises the chance of passing GBS ([MedlinePlus](https://medlineplus.gov/ency/patientinstructions/000511.htm)).
- **Normal:** feeling hot, which the NHS lists for these weeks ([NHS](https://www.nhs.uk/best-start-in-life/pregnancy/week-by-week-guide-to-pregnancy/3rd-trimester/week-36/)). **Call your provider** for a fever of 100.4°F (38°C) or higher ([CDC](https://www.cdc.gov/hearher/maternal-warning-signs/index.html)); a fever in labor is another GBS risk factor ([MedlinePlus](https://medlineplus.gov/ency/patientinstructions/000511.htm)).
- **Normal:** getting short of breath more easily in the third trimester ([OWH](https://womenshealth.gov/pregnancy/youre-pregnant-now-what/stages-pregnancy)). **Call 911** for trouble breathing, chest pain, or a fast-beating heart; the CDC lists each as an urgent warning sign ([CDC](https://www.cdc.gov/hearher/maternal-warning-signs/index.html)).

## For you

There is no vaccine to protect women and babies from GBS ([MedlinePlus](https://medlineplus.gov/ency/patientinstructions/000511.htm)), and every pregnancy needs its own test, whatever your last result was ([AAP](https://www.healthychildren.org/English/ages-stages/prenatal/Pages/Get-Tested-for-Group-B-Strep.aspx)). If you test positive, you can still breastfeed ([AAP](https://www.healthychildren.org/English/ages-stages/prenatal/Pages/Get-Tested-for-Group-B-Strep.aspx)).

If you're the partner: know whether she has a penicillin allergy on file and what the plan is. In labor, you may be the one answering the question.

## Sources

- NHS. "Week 35." Week-by-week guide to pregnancy, Best Start in Life. https://www.nhs.uk/best-start-in-life/pregnancy/week-by-week-guide-to-pregnancy/3rd-trimester/week-35/
- MedlinePlus. "Fetal development." Medical Encyclopedia, National Library of Medicine. https://medlineplus.gov/ency/article/002398.htm
- MedlinePlus. "Group B streptococcus - pregnancy." National Library of Medicine. https://medlineplus.gov/ency/patientinstructions/000511.htm
- American Academy of Pediatrics. "Pregnant Moms: Get Tested for Group B Strep." HealthyChildren.org, 2019. https://www.healthychildren.org/English/ages-stages/prenatal/Pages/Get-Tested-for-Group-B-Strep.aspx
- Office on Women's Health. "Labor and birth." U.S. Department of Health and Human Services. https://womenshealth.gov/pregnancy/childbirth-and-beyond/labor-and-birth
- NHS. "Week 36." Week-by-week guide to pregnancy, Best Start in Life. https://www.nhs.uk/best-start-in-life/pregnancy/week-by-week-guide-to-pregnancy/3rd-trimester/week-36/
- Centers for Disease Control and Prevention. "Urgent Maternal Warning Signs and Symptoms." HEAR HER campaign, 2024. https://www.cdc.gov/hearher/maternal-warning-signs/index.html
- Office on Women's Health. "Stages of pregnancy." U.S. Department of Health and Human Services. https://womenshealth.gov/pregnancy/youre-pregnant-now-what/stages-pregnancy