Third Trimester Pregnancy Dos and Don'ts: A Complete Guide

Quick take: In the third trimester, focus on balanced nutrition, gentle exercise, steady weight gain, safe sleep positions, and regular prenatal visits. Avoid high‑risk foods, listen to your body for labor signs, and pack a hospital bag early. Most of these dos and don’ts keep you and baby healthy, but always check with your provider if anything feels unusual.

It’s 10 p.m., you’ve just felt that familiar “twinge” in your lower belly, and the internet is buzzing with advice about what’s normal in the last months of pregnancy. You’re not alone—many expectant parents wonder which habits truly help and which could cause trouble as the due date looms.

In the third trimester, the little changes you make each day add up to big benefits for you and your baby. This guide walks you through the most common questions—what to eat, how to move, when to see your doctor, and how to prepare for the birth day—so you can feel confident about every decision.

Read on for clear, evidence‑based answers, practical tips you can start using tonight, and a handy checklist for the hospital stay. All the advice aligns with guidance from ACOG, the NHS, and WHO, and we’ve highlighted the moments when a quick call to your provider is the safest move.

What foods should I avoid in the third trimester pregnancy?

Why certain foods can be risky

During the final stretch, your body’s immune system is slightly more tolerant, but some foods still pose a higher risk of food‑borne illness or excess nutrients that could stress you. The main culprits are:

• Unpasteurized dairy and soft cheeses (e.g., brie, feta, queso fresco) that can harbor Listeria—a bacterium linked to miscarriage and stillbirth.
• Raw or undercooked animal products such as sushi with raw fish, rare steak, or partially cooked eggs, which may contain Salmonella or Campylobacter.
• High‑mercury fish like shark, swordfish, king mackerel, and tilefish; mercury can affect fetal brain development.
• Unwashed fruits and vegetables that might carry Toxoplasma parasites.
• Excess caffeine (more than 200 mg per day) because it can slightly increase the risk of low birth weight.
• Alcohol—no safe amount has been established, and it can lead to fetal alcohol spectrum disorders.

Safe nutrition and a sample diet plan

Focus on foods that boost iron, calcium, omega‑3s, and folate while keeping you satisfied. A typical day might look like this:

• Breakfast: Whole‑grain toast with avocado, a boiled egg, and a glass of fortified orange juice (calcium‑rich).
• Mid‑morning snack: Greek yogurt with berries and a sprinkle of chia seeds.
• Lunch: Quinoa salad with roasted sweet potatoes, spinach, chickpeas, and a drizzle of olive oil.
• Afternoon snack: A handful of almonds and an apple.
• Dinner: Baked salmon (low‑mercury) with steamed broccoli and brown rice.
• Evening snack (if needed): A small bowl of cottage cheese with pineapple.

These meals provide roughly 2,200–2,500 kcal, 30 g of protein, 1,200 mg of calcium, 400 µg of folate, and 200 mg of DHA—nutrients highlighted by the ACOG Committee on Nutrition for the third trimester.

Best prenatal vitamins for the third trimester

Even with a balanced diet, a prenatal vitamin helps fill any gaps. Look for a product that includes:

• Iron (27 mg) to support the expanding blood volume.
• Calcium (1,000 mg) and vitamin D (600 IU) for bone health.
• Folate (800 µg) and vitamin B12.
• Omega‑3 DHA (200–300 mg) for brain development.

Both the NHS and the American College of Obstetricians and Gynecologists recommend a daily prenatal vitamin that meets these thresholds. If you have a specific deficiency (e.g., iron‑deficiency anemia), your provider may prescribe a higher‑dose supplement.

Which exercises are safe in the third trimester pregnancy?

Regular activity helps reduce back pain, improve circulation, and prepare your body for labor. ACOG advises pregnant people to aim for at least 150 minutes of moderate‑intensity aerobic activity per week, unless contraindicated.

“Moderate‑intensity” means you can talk but not sing while moving. Walking, swimming, and stationary cycling fit this definition well. The NHS adds that low‑impact activities are especially safe after 28 weeks.

Examples of safe workouts

• Walking – 30‑minute brisk walks most days, preferably on flat surfaces.
• Prenatal yoga – Focus on gentle stretches, breathing, and pelvic‑floor activation.
• Swimming or water aerobics – The buoyancy reduces joint stress and eases swelling.
• Stationary cycling – Keep resistance low and avoid high‑speed sprints.
• Strength training – Light dumbbells (≤5 lb) for upper‑body work, using proper form.

How to modify if you feel discomfort

If you notice shortness of breath, dizziness, or uterine contractions, stop immediately, sit down, and sip water. A quick talk test can tell you if you’re pushing too hard—if you’re gasping, slow down.

For back pain, try pelvic‑tilt exercises on a stability ball or side‑lying leg lifts. A warm shower before a walk can also loosen tight muscles.

How much weight should I gain in the third trimester?

Weight gain is not a single number; it depends on your pre‑pregnancy body‑mass index (BMI). The Institute of Medicine (IOM) outlines the following total‑gain ranges:

Most of the gain occurs in the third trimester because the baby’s brain, lungs, and fat stores accelerate. Aim for a steady increase—rapid spikes may indicate excess fluid retention or gestational diabetes.

Track your weight at each prenatal visit. If you’re gaining more than the weekly target for two consecutive appointments, discuss dietary adjustments with your provider.

What are the signs of preterm labor in the third trimester pregnancy?

Early warning signs

Preterm labor can begin as early as 20 weeks, but the most common window is 28–36 weeks. Watch for:

• Regular uterine contractions (every 5–10 minutes) lasting 30–60 seconds.
• Persistent lower‑back pressure that doesn’t ease with rest.
• Change in vaginal discharge—especially a watery, mucus‑filled, or bloody fluid.
• Pelvic cramping that feels like menstrual cramps.
• Sudden increase in pelvic or abdominal pain.

Labor signs vs. false alarms

False labor (Braxton‑Hicks) often feels like irregular, “practice” contractions that don’t become progressively stronger or closer together. In true preterm labor, the pattern intensifies over a few hours.

If you experience any combination of the above, especially a change in discharge, call your provider right away. Early intervention—such as steroids for fetal lung maturity—can improve outcomes.

Which sleep positions matter most in the third trimester and why?

Why the left‑side position is recommended

From about 20 weeks onward, the uterus can compress the inferior vena cava when you lie on your back, reducing blood return to the heart. The ACOG advises sleeping on the left side to keep circulation optimal for both you and the baby.

Tips for staying comfortable

• Use a full‑length body pillow or a wedge pillow behind your back to keep you from rolling onto your back.
• Place a pillow between your knees to align the hips and lessen lower‑back strain.
• Wear a loose, breathable nightgown to avoid overheating.
• If you wake up on your back, simply shift back to your left side; there’s no need for a panic‑inducing “sleep study.”

When side‑sleeping isn’t possible

Some people find it hard to stay on one side all night. The NHS notes that occasional back‑sleep is acceptable if you’re otherwise comfortable, but try to return to the side as soon as you’re able.

What travel tips should I follow as a third‑trimester pregnant woman?

Air travel considerations

Both the CDC and ACOG consider air travel safe up to 36 weeks for uncomplicated pregnancies. Keep these pointers in mind:

• Choose an aisle seat for easier bathroom access.
• Wear compression stockings to reduce swelling and deep‑vein thrombosis risk.
• Stay hydrated—drink a cup of water every hour.
• Move your legs every 30 minutes (heel‑toe circles or short walks down the aisle).
• Bring a copy of your prenatal records in case of emergency.

Driving and long‑distance car trips

Plan for stops every 1‑2 hours to stretch, use the restroom, and walk around. Keep a seatbelt snug under your belly, and avoid sitting for more than 90 minutes without a break.

Traveling abroad

If you’re heading overseas, check the destination’s medical facilities, Zika risk, and vaccination requirements. The WHO advises against travel to areas with high malaria incidence after the first trimester unless you have prophylaxis.

When should I schedule prenatal appointments in the third trimester?

Typical visit timeline

Most providers follow this schedule:

• 28 weeks – Routine check‑up, anatomy scan review, and blood work.
• 32 weeks – Growth assessment, blood pressure, and discussion of birth plan.
• 36 weeks – Cervical check (if indicated), Group B Strep screening, and final vaccine updates.
• 38 weeks – Final ultrasound (if needed), discussion of labor signs, and hospital bag reminder.
• 40 weeks – Weekly or bi‑weekly visits until delivery.

What to expect during the third‑trimester ultrasound

The ACOG ultrasound at 28‑32 weeks confirms fetal growth, placental location, and amniotic fluid volume. It also lets you see the baby’s facial features, practice bonding, and hear the heartbeat—a moment many parents describe as “the most emotional scan.”

Third‑trimester fetal development milestones

By week 28, the baby’s brain continues rapid development, eyes can open and close, and lungs produce surfactant. At 34 weeks, the baby gains about 0.5 lb (225 g) per week and can respond to sounds. By 36 weeks, the majority of body fat is accumulated, and the baby often turns head‑down.

Symptoms timeline and how to manage them

Common discomforts intensify as the uterus expands:

• Back pain – Try a warm‑compress or prenatal‑yoga stretches.
• Heartburn – Eat smaller meals, avoid spicy foods, and stay upright after eating.
• Leg cramps – Stretch calves before bed and stay hydrated.
• Frequent urination – Reduce fluid intake an hour before bedtime.

If any symptom becomes severe (e.g., sudden swelling, severe headaches, or vision changes), contact your provider immediately.

What should I pack for a hospital stay during the third trimester?

Essential items for you

• Comfortable maternity or loose‑fitting nightgown (front‑open for easy nursing).
• Non‑slip socks or slippers.
• Personal toiletries (toothbrush, toothpaste, lip balm, hairbrush).
• Phone charger and a small bag for your hospital ID.
• Any prescribed medications, including prenatal vitamins.

Essentials for the baby

• Two or three newborn outfits (including a hat).
• Soft blanket or swaddle.
• Infant car seat (installed in your car before labor).
• Newborn diapers and wipes (the hospital usually provides a few, but a small supply is handy).

Optional comfort items

• Music playlist or favorite podcast with headphones.
• Reusable water bottle.
• Snacks for your partner or support person.
• Eye mask and earplugs for better sleep.

Pack your bag by week 36 so you’re not scrambling at the last minute. A quick “hospital bag checklist” on your phone can keep you organized.

From our medical team: Every pregnancy is unique. The dos and don’ts listed here reflect broad, evidence‑based guidance, but your provider knows your individual health history best. If you ever feel unsure—whether it’s about a new food, a sudden cramp, or a travel plan—don’t hesitate to call your midwife or obstetrician. A quick check can keep both you and your baby safe.

Myth vs. fact

Myth: You must avoid all carbs in the third trimester.

Fact: Carbohydrates provide essential energy for you and the growing baby. Choose complex carbs like whole grains and fruits, and limit simple sugars.

Myth: If you’re not feeling contractions, labor won’t start until after 40 weeks.

Fact: Some women go into labor naturally before 40 weeks, especially if they have certain risk factors. Regular prenatal visits help monitor timing.

Myth: You can’t travel after the 30th week.

Fact: Air travel is generally safe up to 36 weeks for uncomplicated pregnancies, provided you follow hydration and movement guidelines.

Key takeaways

• Eat a balanced diet, avoid unpasteurized dairy, raw fish, high‑mercury seafood, and excess caffeine.
• Aim for at least 150 minutes of moderate exercise each week; walking, swimming, and prenatal yoga are top choices.
• Target a weekly weight gain of 0.3–0.7 lb (0.15–0.3 kg) depending on pre‑pregnancy BMI.
• Sleep on your left side with supportive pillows to maintain optimal blood flow.
• Travel safely by staying hydrated, moving regularly, and using compression stockings for flights.
• Schedule prenatal visits at 28, 32, 36, and 38 weeks, and keep an eye on labor‑related symptoms.
• Pack your hospital bag by week 36, including comfort items for both you and the newborn.

Frequently asked questions

What are the warning signs of complications in the third trimester?

Sudden swelling of hands or face, severe headaches, vision changes, persistent abdominal pain, or a gush of fluid are red‑flag symptoms; call your provider immediately.

Can I continue to exercise during the third trimester?

Yes—moderate activities like walking, swimming, and gentle prenatal yoga are safe; just avoid high‑impact or contact sports and listen to your body.

How much weight is safe to gain in the third trimester?

Most guidelines recommend a steady gain of 0.5 lb (0.2 kg) per week for normal‑weight individuals, with total third‑trimester gain of about 7–10 lb (3–4.5 kg).

When should I start packing my hospital bag?

Begin assembling your bag by week 36 so you have time to add any last‑minute items and avoid stress as labor approaches.

Is it safe to travel by plane in the third trimester?

Air travel is generally considered safe up to 36 weeks for uncomplicated pregnancies; stay hydrated, move your legs frequently, and wear a seatbelt under your belly.

What foods should I avoid during the third trimester?

Steer clear of unpasteurized dairy, raw or undercooked meats and eggs, high‑mercury fish, unwashed produce, and excessive caffeine or alcohol.

When to call your doctor

If you notice any of the following, contact your provider right away: sudden swelling, severe headache or visual disturbances, persistent abdominal pain, regular contractions before 37 weeks, leaking fluid, or a fever over 100.4 °F (38 °C). This article is for general information only and does not replace personalized medical advice.

References

1. American College of Obstetricians and Gynecologists. “Nutrition During Pregnancy.” ACOG Committee Opinion, 2023.
2. National Health Service (NHS). “Eating well during pregnancy.” Updated 2022.
3. World Health Organization. “Guidelines on maternal health.” WHO Publication, 2021.
4. Centers for Disease Control and Prevention. “Pregnancy and travel safety.” CDC Health Information, 2023.
5. Mayo Clinic. “Third trimester weight gain.” Mayo Clinic Proceedings, 2022.
6. Royal College of Obstetricians and Gynaecologists (RCOG). “Management of preterm labor.” RCOG Green-top Guideline, 2020.
7. Institute of Medicine. “Weight Gain During Pregnancy: Reexamining the Guidelines.” National Academies Press, 2009.
8. U.S. Food and Drug Administration (FDA). “Guidance for industry: Food safety for pregnant women.” FDA Consumer Update, 2022.
9. American Academy of Pediatrics. “Safe travel during pregnancy.” AAP Policy Statement, 2021.
10. Harvard Health Publishing. “Exercise during pregnancy.” Harvard Medical School, 2023.