# Third Trimester for Dads: What's Happening and What to Do

> What happens to the baby and your partner in weeks 28 to 40, the visits, tests and vaccines to expect, the decisions to make together, and the warning signs that mean call now.

By Yoedhistiera, Bapak Life. Topic: Pregnancy. Published October 29, 2026.
Canonical: https://bapaklife.com/third-trimester-for-dads/

## Key takeaways

- The third trimester runs from week 28 to the due date and beyond. ACOG says it's usually the most uncomfortable part of pregnancy for her.
- Prenatal visits go to every 2 weeks, then every week from week 36. Expect the Group B strep test at 36 to 37 weeks, and vaccines for her: Tdap at 27 to 36 weeks and, in season, RSV at 32 to 36 weeks.
- Your list: car seat installed and checked, pediatrician chosen, bag packed, your own Tdap and flu shots, and decisions on cord blood and circumcision.
- A change in the baby's movement, sudden swelling of her face or hands, a headache that won't go away or vision changes mean calling her provider right away.

The third trimester for dads is when the to-do list gets real. The baby is putting on weight fast, your partner is getting more uncomfortable by the week, and the appointments speed up. It's also the stretch where a dad can take the most off her plate. This guide covers what's happening with the baby and with her, the visits and tests to expect, the decisions you'll make together, and the warning signs to know.

Earlier along? See [the first trimester](/first-trimester-for-dads/) or [the second trimester for dads](/second-trimester-for-dads/).

## The short answer

- **When is it?** Week 28 until the birth, according to ACOG. Full term is 39 weeks 0 days to 40 weeks 6 days.
- **What's new?** The baby gains weight quickly and usually turns head down by about week 36 or 37. She'll likely be short of breath, tired and up at night.
- **Appointments:** every 2 weeks, then weekly from week 36, with the Group B strep test at 36 to 37 weeks.
- **Your list:** car seat installed and checked, pediatrician chosen, bag packed, your vaccines, and decisions on cord blood and circumcision.
- **Call right away for:** a change in the baby's movement, sudden swelling of her face or hands, a headache that won't go away, vision changes, bleeding, or signs of labor before 37 weeks.

## How the third trimester is counted

The American College of Obstetricians and Gynecologists (ACOG) counts the third trimester from 28 weeks 0 days to 40 weeks 6 days. The federal Office on Women's Health starts it at week 29, so your app may say something slightly different.

"Due date" and "full term" aren't the same thing. ACOG and the Society for Maternal-Fetal Medicine use these labels:

| Label | Weeks |
|---|---|
| Early term | 37 weeks 0 days to 38 weeks 6 days |
| Full term | 39 weeks 0 days to 40 weeks 6 days |
| Late term | 41 weeks 0 days to 41 weeks 6 days |
| Postterm | 42 weeks and beyond |

If the pregnancy reaches 41 weeks, ACOG says her ob-gyn may recommend extra testing and may recommend inducing labor.

## What's happening with the baby

From ACOG's week-by-week guide:

- **Week 31:** major development is finished, and the baby is gaining weight very quickly.
- **Weeks 36 to 37:** most babies turn head down for birth.
- **Weeks 37 to 40:** the lungs, brain and nervous system are finishing their development.
- **Week 40:** the head may have dropped lower into her pelvis.

**How big?**

| By the end of | Length | Weight |
|---|---|---|
| Week 28 | Nearly 15 inches | About 2½ pounds |
| Week 32 | Almost 17 inches | A little more than 4 pounds |
| Week 36 | About 18 inches | A little more than 6 pounds |
| Week 40 | About 20 inches | 7½ to 8 pounds |

**If the baby is breech** (bottom or feet first), ACOG says this happens in 3 to 4% of full-term births. After 36 weeks her provider may suggest trying to turn the baby from the outside, a procedure called external cephalic version.

## What's happening with her

ACOG's guide for partners says weeks 28 to 40 are usually the most uncomfortable part of pregnancy. The Office on Women's Health explains why: as the baby gets bigger, it puts more pressure on her organs, so many women find breathing harder and need the bathroom even more often. Other common changes it lists:

- **Heartburn,** which is more common later in pregnancy as the uterus pushes on the stomach.
- **Mild swelling** of the ankles, fingers and face, more noticeable near the due date.
- **Trouble sleeping,** from the baby's movements, bathroom trips and leg cramps. Exhaustion often comes back in the third trimester.
- **Back pain,** from the extra weight on her muscles and joints, according to MedlinePlus.
- **Braxton Hicks contractions,** the "practice" ones, which ACOG says can happen for many weeks before real labor. See [when to go to the hospital for labor](/when-to-go-to-the-hospital-for-labor/) for how to tell them apart.

**Where you come in:** take over the lifting, the groceries and anything that needs bending down. Offer the back rub. Take the night jobs that are yours to take, like the dog or the toddler, so she gets every hour of sleep she can.

## Appointments and tests

**More visits.** MedlinePlus says prenatal visits are every 2 weeks until week 36, then every week, and that it's fine to bring her partner. Her provider will check her weight, blood pressure and the size of her belly, find the baby's position, and talk about the birth. These are good visits to go to: you'll hear the plan first-hand.

**Group B strep test, 36 to 37 weeks.** ACOG recommends testing every pregnant woman for Group B streptococcus (GBS) between 36 weeks 0 days and 37 weeks 6 days, with a swab from the vagina and rectum. ACOG says about 1 in 4 pregnant women carry GBS. If she tests positive, she'll get antibiotics through an IV once labor starts, to protect the baby. Make sure the hospital has the result.

**If she's Rh-negative,** ACOG says she'll usually get a shot of Rh immunoglobulin at 28 weeks and another within 72 hours after the birth if the baby is Rh-positive. The baby can inherit the Rh factor from either parent, so your blood type is part of this.

**Extra monitoring** isn't for everyone. ACOG says tests like the non-stress test are for higher-risk pregnancies and usually start between 32 and 34 weeks.

## Vaccines in the third trimester

**For her,** from the CDC and ACOG's 2026 maternal immunization schedule:

- **Tdap (whooping cough):** between 27 and 36 weeks, in every pregnancy, preferably early in that window.
- **RSV:** the CDC recommends the maternal RSV vaccine at 32 to 36 weeks if she's pregnant during September through January in most of the US. Babies can get an RSV antibody shot instead, and the CDC says most babies don't need both. Decide with her provider and your pediatrician.
- **Flu and COVID-19:** ACOG recommends both during pregnancy.

**For you:** ACOG's guide for partners says you need a Tdap shot at least 2 weeks before the baby is born if you haven't had one, and a flu shot if it's flu season (October to May). Vaccinating the people around a newborn is called "cocooning." The CDC still recommends it, though its vaccine advisers say the evidence that cocooning alone protects the baby is inconclusive; the main protection is her Tdap shot during pregnancy.

## Your third-trimester to-do list

1. **Install the car seat, then get it checked.** ACOG is blunt: you can't take the baby home without an infant car seat. The American Academy of Pediatrics (AAP) suggests working with a certified child passenger safety technician before the baby is born, and registering the seat with the maker so you hear about recalls. Step by step: [how to install an infant car seat](/how-to-install-infant-car-seat/).
2. **Choose a pediatrician.** The AAP recommends that parents-to-be visit a pediatrician during the third trimester.
3. **Pack the bag.** See our [hospital bag checklist for dads](/hospital-bag-checklist-for-dads/).
4. **Tour the hospital and plan the route.** ACOG suggests asking who can be in the room, whether you can stay overnight, and where to park and check in.
5. **Talk through her birth preferences.** MedlinePlus suggests thinking of a birth plan as preferences, not a script, sharing it with her provider well before the due date and taking a copy to the hospital. Ask her what she wants from you: who cuts the cord, whether you stay if she needs a C-section, what to say to visitors.
6. **Learn infant CPR.** MedlinePlus says all parents and caregivers should learn infant and child CPR.
7. **Sort your leave.** Confirm the dates and paperwork with your employer. See [paternity leave in the US](/paternity-leave-in-the-us/).
8. **Get the basics ready.** See [newborn essentials for dads](/newborn-essentials-for-dads/) for what you need for the first weeks.
9. **Finish the registry.** Our [baby registry checklist](/baby-registry-checklist-for-dads/) has quantities and what to skip.
10. **Call the insurer.** Ask about your deductible and how to add the baby. See [what it costs to have a baby](/cost-of-having-a-baby/).

## Decisions to make together

**Cord blood banking.** You can donate the baby's cord blood to a public bank, store it in a private bank, or do neither. From ACOG:

- Public banks don't charge to store cord blood, and it can be used by anyone who matches.
- Private banks charge a yearly fee.
- ACOG says storing a child's cord blood privately as "insurance" against future disease is not recommended.
- If you want to do it, tell the bank and get a collection kit usually 6 weeks or more before the due date. Not all hospitals offer it.

**Circumcision, if it's a boy.** ACOG says it's the parents' choice, not required by law or hospital policy, and may not be covered by insurance. The AAP's position is that the health benefits outweigh the risks, but aren't great enough to recommend it for every baby boy. Talk it over with her provider and your pediatrician before the birth so you're not deciding in the hallway.

**Feeding.** If she plans to breastfeed, ACOG suggests ways a partner can share in it: bring the baby to her for feeds, burp and change the baby, and feed pumped milk later on. Ask the hospital about lactation help before you need it. More in our guide to [night feeds for dads](/night-feeds-for-dads/).

## When to call her provider right away

Don't wait for the next appointment for any of these. From the CDC, ACOG and MedlinePlus:

- **A change in the baby's movement.** The CDC says there's no specific normal number of kicks: a change is what matters. MedlinePlus suggests that if the baby suddenly seems to move less, she eats a snack and lies down for a few minutes, and calls if there's still not much movement. Her provider may also ask her to do kick counts.
- **Sudden or extreme swelling of her face or hands,** or gaining a lot of weight very quickly, which the Office on Women's Health says can be a sign of preeclampsia. The CDC notes this is different from the usual mild swelling of late pregnancy.
- **A headache that won't go away, vision changes,** or pain in the upper belly or shoulder, also possible signs of preeclampsia, according to ACOG.
- **Trouble breathing or chest pain.** Some breathlessness is normal; this is more.
- **Bleeding, fever, chills or burning when she urinates.**
- **Her water breaking, or regular painful contractions.** Before 37 weeks, any sign of labor means calling now.

## Look after yourself too

You're allowed to feel this. A 2019 systematic review of studies on fathers found their anxiety tended to rise through pregnancy and peak around the birth, then fall. A review of 23 studies put anxiety in fathers around the birth at about 1 in 10, though it varied a lot from study to study. Fear of the birth itself and worry about not knowing how to care for a baby came up often. Knowing what's coming helps, which is why you're reading this. If it doesn't ease after the baby arrives, see [postpartum depression in dads](/postpartum-depression-in-dads/).

**After the birth,** ACOG recommends that she has contact with her ob-gyn within the first 3 weeks, not just a single check at 6 weeks, and the CDC's urgent warning signs apply for a year after the birth. Put the dates in your calendar too.

## FAQ

### What should dads do in the third trimester?

Install the car seat and have it checked, choose a pediatrician, pack the hospital bag, get your own Tdap and flu shots, tour the hospital, talk through her birth preferences, and decide on cord blood and circumcision. Go to as many of the visits as you can.

### When does the third trimester start?

ACOG counts it from 28 weeks 0 days to 40 weeks 6 days. Some sources, like the Office on Women's Health, start it at week 29.

### How often are prenatal visits in the third trimester?

MedlinePlus says every 2 weeks until week 36, then every week until the birth.

### Does dad need vaccines before the baby is born?

ACOG says partners need a Tdap shot at least 2 weeks before the birth if they haven't had one, plus a flu shot in flu season. The CDC recommends vaccinating people in close contact with a newborn.

### When is the baby full term?

At 39 weeks 0 days. ACOG calls 37 to 38 weeks early term and 39 to 40 weeks full term.

### Is it normal for the baby to move less at the end of pregnancy?

MedlinePlus says the pattern of movement changes as the baby grows, but she should still feel the baby move often during the day. The CDC says a change in movement is what matters. If it seems to drop, call her provider.

## Sources

- [A Partner's Guide to Pregnancy](https://www.acog.org/womens-health/faqs/a-partners-guide-to-pregnancy), [How Your Fetus Grows During Pregnancy](https://www.acog.org/womens-health/faqs/how-your-fetus-grows-during-pregnancy), [Changes During Pregnancy](https://www.acog.org/womens-health/infographics/changes-during-pregnancy), [If Your Baby Is Breech](https://www.acog.org/womens-health/faqs/if-your-baby-is-breech), [When Pregnancy Goes Past Your Due Date](https://www.acog.org/womens-health/faqs/when-pregnancy-goes-past-your-due-date), [Group B Strep and Pregnancy](https://www.acog.org/womens-health/faqs/group-b-strep-and-pregnancy), [The Rh Factor](https://www.acog.org/womens-health/faqs/the-rh-factor-how-it-can-affect-your-pregnancy), [Special Tests for Monitoring Fetal Well-Being](https://www.acog.org/womens-health/faqs/special-tests-for-monitoring-fetal-well-being), [Preeclampsia and High Blood Pressure During Pregnancy](https://www.acog.org/womens-health/faqs/preeclampsia-and-high-blood-pressure-during-pregnancy), [Cord Blood Banking](https://www.acog.org/womens-health/faqs/cord-blood-banking), [Newborn Male Circumcision](https://www.acog.org/womens-health/faqs/newborn-male-circumcision), [Breastfeeding Your Baby](https://www.acog.org/womens-health/faqs/breastfeeding-your-baby) and [How to Tell When Labor Begins](https://www.acog.org/womens-health/faqs/how-to-tell-when-labor-begins), American College of Obstetricians and Gynecologists
- [Definition of Term Pregnancy (Committee Opinion No. 579)](https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2013/11/definition-of-term-pregnancy), [Prevention of Group B Streptococcal Early-Onset Disease in Newborns (Committee Opinion No. 797)](https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2020/02/prevention-of-group-b-streptococcal-early-onset-disease-in-newborns), [Optimizing Postpartum Care (Committee Opinion No. 736)](https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2018/05/optimizing-postpartum-care) and [Maternal Immunizations (Committee Statement No. 26)](https://www.acog.org/clinical/clinical-guidance/committee-statement/articles/2026/02/maternal-immunizations), ACOG
- [Prenatal care in your third trimester](https://medlineplus.gov/ency/patientinstructions/000558.htm), [What to include in your birth plan](https://medlineplus.gov/ency/patientinstructions/000567.htm) and [CPR: infant](https://medlineplus.gov/ency/article/000011.htm), MedlinePlus (National Library of Medicine)
- [Stages of pregnancy](https://womenshealth.gov/pregnancy/youre-pregnant-now-what/stages-pregnancy) and [Body changes and discomforts](https://womenshealth.gov/pregnancy/youre-pregnant-now-what/body-changes-and-discomforts), Office on Women's Health (HHS)
- [Immunizations to Protect Infants](https://www.cdc.gov/rsv/vaccines/protect-infants.html), [Vaccinating Pregnant Patients (pertussis)](https://www.cdc.gov/pertussis/hcp/vaccine-recommendations/vaccinating-pregnant-patients.html) and [Urgent Maternal Warning Signs](https://www.cdc.gov/hearher/maternal-warning-signs/index.html), Centers for Disease Control and Prevention
- [Car Seats: Information for Families](https://www.healthychildren.org/English/safety-prevention/on-the-go/Pages/Car-Safety-Seats-Information-for-Families.aspx) and [Expectant Parents Encouraged to Visit Pediatrician Before Birth of Baby](https://www.healthychildren.org/English/news/Pages/Expectant-Parents-Encouraged-to-Visit-Pediatrician-Before-Birth-of-Baby.aspx), American Academy of Pediatrics (HealthyChildren.org)
- [Anxiety in fathers in the perinatal period: a systematic review](https://pubmed.ncbi.nlm.nih.gov/31176080/), Philpott et al., *Midwifery*, 2019
- [Anxiety among fathers during the prenatal and postpartum period: a meta-analysis](https://pubmed.ncbi.nlm.nih.gov/33632067/), Leiferman et al., *Journal of Psychosomatic Obstetrics and Gynecology*, 2021
- [Stress in fathers in the perinatal period: a systematic review](https://pubmed.ncbi.nlm.nih.gov/28992554/), Philpott et al., *Midwifery*, 2017