Third Trimester Guide: Weeks 28–40 of Pregnancy

The third trimester (weeks 28–40) is the home stretch — your baby is gaining weight rapidly, your body is preparing for labor, and the nesting instinct is in full swing. These final weeks bring their own set of challenges, from Braxton Hicks contractions to trouble sleeping, but they're also filled with anticipation and preparation.

This guide covers everything from baby's final development stages to labor preparation, hospital bag packing, and knowing when it's time to call your provider.

Baby's Final Growth Spurt

Your baby enters the third trimester weighing about 2.5 pounds and measuring roughly 15 inches. Over the next 12 weeks, your baby will more than double in weight and add several inches. By week 32, your baby's bones are fully formed (though still soft), and they're practicing breathing movements. Weeks 33–36 bring rapid brain development — the brain grows by about one-third during this period.

By week 37, your baby is considered "early term." The lungs are mature, and your baby is spending time in the head-down position preparing for birth. At week 39 ("full term"), the average baby weighs 7–8 pounds and is about 20 inches long. The final weeks are critical for brain development, fat accumulation for temperature regulation, and lung maturity.

Your Body in the Third Trimester

Braxton Hicks contractions become noticeable — these "practice contractions" feel like your belly tightening and relaxing. They're irregular, don't increase in intensity, and usually stop with position changes or hydration. True labor contractions are regular, get closer together, increase in intensity, and don't stop with movement.

Sleep becomes challenging. The Sleep Foundation reports that up to 78% of pregnant people experience sleep disturbances in the third trimester. Sleep on your side (left side is ideal for blood flow), use a pregnancy pillow between your knees, and limit fluids before bed. Heartburn, frequent urination, and restless legs are common sleep disruptors.

Swelling in the feet and ankles (edema) is normal and caused by increased blood volume and fluid retention. Elevate your feet, stay active, drink plenty of water (counterintuitive but it helps), and wear comfortable, supportive shoes. Sudden severe swelling — especially in the face and hands — along with headache or vision changes may indicate preeclampsia and requires immediate medical evaluation.

Prenatal Visits & Tests

Prenatal visits increase in frequency: every two weeks from weeks 28–36, then weekly from weeks 36–40. At week 36, your provider will check your baby's position (head-down or breech) and do a Group B Strep (GBS) test — a vaginal and rectal swab testing for a common bacteria that can be passed to baby during vaginal birth. If positive (about 25% of people are), you'll receive IV antibiotics during labor.

Your provider will also begin checking for cervical changes (dilation and effacement) in the final weeks. Keep in mind that you can be 3cm dilated for weeks or go from 0 to delivery in hours — cervical checks are snapshots, not predictors. According to ACOG, true labor begins when contractions cause progressive cervical change.

Preparing for Labor & Delivery

Take a childbirth education class between weeks 28–32. These cover the stages of labor, pain management options, breathing techniques, and what to expect during delivery. Many hospitals offer free or low-cost classes, and online options are available from organizations like Lamaze International.

Write a birth plan or birth preferences document. This isn't a rigid script — it's a communication tool for your care team. Include your preferences for pain management, who you want in the room, immediate skin-to-skin contact, cord clamping timing, and feeding plans. Be flexible — labor doesn't always follow the plan, and that's okay. See our hospital bag checklist for what to pack.

Hospital Bag Essentials

Pack your bag by week 36. For you: comfortable robe, nursing bra, going-home outfit (maternity-sized, not pre-pregnancy), toiletries, phone charger with a long cord, snacks, and any comfort items (pillow, essential oils, music playlist). For baby: going-home outfit, car seat (installed and inspected before labor), a swaddle blanket, and a hat. For your partner: change of clothes, snacks, charger, and a pillow.

Don't forget: insurance card, ID, birth plan copies, and any medications you take. Most hospitals provide diapers, wipes, and basic supplies for your stay, but confirm with your facility.

Warning Signs to Watch For

Contact your provider immediately if you experience regular contractions before week 37 (preterm labor), a gush or steady trickle of fluid (possible ruptured membranes), vaginal bleeding, severe headache with vision changes (preeclampsia signs), decreased fetal movement (fewer than 10 movements in 2 hours during a kick count), or severe abdominal pain that doesn't resolve.

Call 911 for heavy bleeding, seizures, difficulty breathing, or loss of consciousness.

Frequently Asked Questions

How do I know if I'm in real labor?

Real contractions follow the 5-1-1 rule: contractions every 5 minutes, lasting 1 minute each, for at least 1 hour. They get progressively stronger and closer together, and don't stop when you change positions or drink water. Braxton Hicks contractions are irregular and stop with rest.

What if my baby is breech at 36 weeks?

About 3–4% of babies are breech at term. Your provider may suggest an external cephalic version (ECV) — a procedure to manually turn the baby. Success rates are about 50–60%. If the baby remains breech, a planned C-section is typically recommended. Some providers are experienced in vaginal breech deliveries — discuss options with your care team.

When should I go to the hospital?

Follow the 5-1-1 rule for first-time parents. If your water breaks (even without contractions), call your provider — most recommend going to the hospital within a few hours. Go immediately if the fluid is green or brown (possible meconium), you're bleeding heavily, or you're less than 37 weeks.

What is the "bloody show"?

A small amount of blood-tinged mucus passed from the cervix as it begins to dilate. It can appear days or hours before labor starts and is a normal sign that your body is preparing. It's different from heavy bleeding, which warrants immediate medical attention.

Can I still exercise in the third trimester?

Yes, with modifications. Walking, swimming, and prenatal yoga remain excellent choices. Listen to your body — you may need to reduce intensity. Stop exercising and contact your provider if you experience dizziness, headache, chest pain, contractions, or vaginal bleeding.