# Day 197: Rh, and the 28-week shot

> Twenty-eight weeks and one day. One line on your blood test result decides whether you need a shot around now. Today you find that line.

- Series: Your seventh month of pregnancy, day by day (https://chorevia.com/learn/pregnancy-month-7), day 197 of 280, 28 weeks + 1 day
- Your baby this week: about the size of an aubergine; around 37.6 cm from head to heel
- Canonical URL: https://chorevia.com/learn/pregnancy-month-7/day-197
- Last reviewed: 2026-10-22
- Publisher: Chorevia (https://chorevia.com)
- Cite as: Chorevia. "Day 197: Rh, and the 28-week shot." Last reviewed October 22, 2026. https://chorevia.com/learn/pregnancy-month-7/day-197

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.

Twenty-eight weeks and one day. Today is about a single word on a lab result from your first visit: positive or negative. For most people it changes nothing. For some it means one injection around now, and it's worth knowing which you are.

## Your baby

Your baby's heart has been changing pace all along. The NHS says it was about 110 beats a minute around weeks 5 to 6, when it could first be picked up, rose to about 170 in weeks 9 and 10, and has now slowed to about 140 ([NHS](https://www.nhs.uk/best-start-in-life/pregnancy/week-by-week-guide-to-pregnancy/3rd-trimester/week-28/)). Length around now: around 37.6cm from head to heel, about the size of an aubergine ([NHS](https://www.nhs.uk/best-start-in-life/pregnancy/week-by-week-guide-to-pregnancy/3rd-trimester/week-28/)).

## Your body

Your blood type and Rh factor were checked at your first prenatal visit ([OWH](https://womenshealth.gov/pregnancy/youre-pregnant-now-what/prenatal-care-and-tests)). If you are Rh-negative, MedlinePlus says you may need an injection of RhoGAM around 28 weeks ([MedlinePlus](https://medlineplus.gov/ency/patientinstructions/000557.htm)).

Here's why. Rh incompatibility develops when the pregnant woman is Rh-negative and her baby is Rh-positive: the baby's red blood cells can cross the placenta, and her body may make antibodies that destroy them, which can cause jaundice in the newborn ([MedlinePlus](https://medlineplus.gov/ency/article/001600.htm)). RhoGAM prevents that. It's given in pregnancy if the baby's father is Rh-positive or his type is unknown, with a second dose within a few days after delivery if the baby turns out to be Rh-positive ([MedlinePlus](https://medlineplus.gov/ency/article/001600.htm)). MedlinePlus's verdict is reassuring: "Rh incompatibility is almost completely preventable" ([MedlinePlus](https://medlineplus.gov/ency/article/001600.htm)).

## Try today

### The RhoGAM question

- **Time:** 5 minutes

1. Find your blood type in your notes or patient portal. You're looking for a plus or minus sign, or the words Rh-positive or Rh-negative.
2. If you're Rh-positive, cross this off. There is nothing to schedule.
3. If you're Rh-negative, ask at your next visit when your RhoGAM shot is booked, and write the date down.
4. Ask whether your partner's blood type matters for your plan, since MedlinePlus ties the decision to the father's type ([MedlinePlus](https://medlineplus.gov/ency/article/001600.htm)).

**Make it work:** Rh-negative women should get RhoGAM in every pregnancy ([MedlinePlus](https://medlineplus.gov/ency/article/001600.htm)), so a shot last time doesn't cover this one.

## Watch for

- **Normal:** bumping into a doorframe or a counter edge now that you're wider than you used to be. **Call your provider** after a fall or a blow to your belly, and say if you're Rh-negative: MedlinePlus lists abdominal injury as a reason for RhoGAM ([MedlinePlus](https://medlineplus.gov/ency/article/001600.htm)).
- **Normal:** a nosebleed, which the NHS says can even happen while you sleep at this stage ([NHS](https://www.nhs.uk/best-start-in-life/pregnancy/week-by-week-guide-to-pregnancy/3rd-trimester/week-28/)). **Call your provider** right away for dizziness or fainting ([CDC](https://www.cdc.gov/hearher/maternal-warning-signs/index.html)).
- **Normal:** the occasional queasy morning. **Call your provider** for severe nausea and vomiting: if you can't drink for more than 8 hours or eat for more than 24 ([CDC](https://www.cdc.gov/hearher/maternal-warning-signs/index.html)).

## For you

A minus sign on a lab result can look like a problem. Here it's just a blood type, and the plan for it is routine: Rh-negative mothers "should be followed closely by their providers during pregnancy" ([MedlinePlus](https://medlineplus.gov/ency/article/001600.htm)), which is what is already happening.

If you're the partner: do you know your blood type? If you do, say so. If you don't, that's fine too; the guidance covers an unknown type ([MedlinePlus](https://medlineplus.gov/ency/article/001600.htm)). Either way, put the shot date in your calendar as well as hers.

## Sources

- NHS. "Week 28." 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-28/
- Office on Women's Health. "Prenatal care and tests." U.S. Department of Health and Human Services. https://womenshealth.gov/pregnancy/youre-pregnant-now-what/prenatal-care-and-tests
- MedlinePlus. "Prenatal care in your second trimester." National Library of Medicine. https://medlineplus.gov/ency/patientinstructions/000557.htm
- MedlinePlus. "Rh incompatibility." Medical Encyclopedia, National Library of Medicine. https://medlineplus.gov/ency/article/001600.htm
- 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