Quick take: At 31 weeks pregnant you’re deep into the third trimester. Your baby is about the size of a cantaloupe, weighing roughly 3 lb 5 oz (1.5 kg) and measuring 16 inches (41 cm). Expect common third‑trimester symptoms—backaches, leg cramps, swelling, and more—plus a few key prenatal visits. Stay hydrated, keep moving with safe exercises, and watch for warning signs like bleeding or severe pain. Use this guide to know what’s normal, what to eat, how to ease discomfort, and how to prepare for labor.
Imagine it: you’re scrolling through a pregnancy forum at 2 a.m., heart racing because you just felt a flutter and wondered, “Is my baby moving enough?” You’re not alone. Many expectant mothers hit the 31‑week mark feeling a mix of excitement and fatigue, and they crave clear, reassuring answers about what comes next.
In this article we answer the exact question you typed into Google: 31 weeks pregnant what to expect. We’ll walk you through your baby’s development, the symptoms you might be dealing with, nutrition and exercise tips, upcoming appointments, signs that need urgent care, and practical steps for labor and a birth plan. All advice is grounded in reputable sources such as the American College of Obstetricians and Gynecologists (ACOG) and the Mayo Clinic.
Read on for a day‑by‑day snapshot, a handy checklist, and a few myths busted along the way. By the end you’ll have a solid roadmap for the weeks ahead, plus a confidence boost that you’re doing everything you can for you and your baby.
What is the baby’s size and development at 31 weeks pregnant?
At 31 weeks, your baby is entering the final stretch of growth before birth. On average, the fetus weighs about 3 lb 5 oz (1.5 kg) and measures 16 inches (41 cm) long—roughly the size of a cantaloupe. The head is still the largest part, but the body is catching up as fat stores increase to help regulate temperature after delivery.
The lungs are maturing rapidly, producing surfactant that will keep the air sacs open once the baby takes its first breath. The brain’s surface folds (gyri) are becoming more pronounced, supporting higher-order functions. Your baby’s eyes can now focus, and the eyelids can open and close. The sense of hearing is fully developed, and the baby can respond to external sounds, especially familiar voices.
Below is a quick reference chart for fetal size at 31 weeks:
These numbers are averages; each baby grows at its own pace. If you’re tracking movements, you should feel more distinct kicks and rolls as the baby has less room to maneuver.
Common symptoms and discomforts at 31 weeks pregnant
Third‑trimester discomforts are common, but they don’t have to dominate your days. Below is a symptoms checklist that many women report around week 31:
- Backaches, especially in the lower back
- Leg cramps, often at night
- Swelling (edema) in ankles, feet, and hands
- Shortness of breath when climbing stairs
- Frequent urination or urgency
- Heartburn or indigestion
- Braxton‑Hill (practice) contractions
- Fatigue and trouble sleeping
How to soothe these discomforts:
- Back pain: Use a maternity support belt, practice gentle pelvic tilts, and keep a pillow between your knees when lying on your side.
- Leg cramps: Stretch calf muscles before bed, stay hydrated, and consider a magnesium supplement after discussing it with your provider.
- Swelling: Elevate feet whenever possible, wear compression socks, and avoid standing for long periods.
- Heartburn: Eat smaller meals, avoid lying down right after eating, and keep a glass of water handy.
Many women find that a warm (not hot) shower before bedtime relaxes muscles and reduces nighttime awakenings. If a symptom feels severe or sudden—like sharp pain, heavy bleeding, or a sudden loss of fetal movement—contact your provider right away.
What foods should I avoid and what should I eat at 31 weeks pregnant?
Nutrition remains a cornerstone of a healthy third trimester. The goal is to support fetal growth while keeping you energized and comfortable.
Foods to limit or avoid:
- Unpasteurized dairy and soft cheeses (risk of Listeria)
- Raw or undercooked eggs, meat, and seafood (risk of salmonella or parasites)
- High‑mercury fish such as shark, swordfish, king mackerel, and tilefish
- Excessive caffeine (>200 mg per day)
- Processed meats high in sodium and nitrates
What to eat (aligned with the Academy of Nutrition and Dietetics recommendations):
- Protein: Lean poultry, beans, lentils, tofu, and low‑fat dairy.
- Iron‑rich foods: Spinach, fortified cereals, and red meat—pair with vitamin C sources (citrus, bell peppers) to boost absorption.
- Calcium: Yogurt, cheese, fortified plant milks, and leafy greens.
- Omega‑3 fatty acids: Low‑mercury fish like salmon, sardines, or algae‑based supplements.
- Fiber: Whole grains, fruits, and vegetables to alleviate constipation.
Stay hydrated—aim for 8‑10 glasses of water daily. If you’re experiencing swelling, a pinch of sea salt in your meals can help maintain electrolyte balance, but keep overall sodium moderate.
How to manage back pain and leg cramps at 31 weeks pregnant
Back pain and leg cramps are among the top complaints at this stage. Below is a treatment options comparison table to help you choose what might work best for you, based on safety and evidence from ACOG and the Mayo Clinic.
In addition to the options above, try these natural remedies with evidence:
- Hydration: Dehydration can trigger cramps; aim for at least 2 L of fluid daily.
- Gentle calf stretches: Sit with legs extended, loop a towel around the ball of the foot, and gently pull toward you.
- Massage: Light self‑massage of the lower back or using a tennis ball against a wall can reduce tension.
Remember to discuss any supplement or new routine with your obstetric provider, especially if you have a history of hypertension or kidney issues.
What prenatal tests and appointments are scheduled at 31 weeks pregnant?
At 31 weeks, most providers will have you on a regular prenatal visit schedule—typically every two weeks until 36 weeks, then weekly. Key appointments and tests include:
- Routine check‑up: Blood pressure, weight, fundal height measurement, and fetal heart rate auscultation.
- Glucose screening (if not done earlier): Some clinicians repeat the test if risk factors develop.
- Group B Streptococcus (GBS) screening: Usually performed between 35‑37 weeks, but some clinics start at 31 weeks for high‑risk patients.
- Ultrasound (optional): To assess fetal growth, placental position, and amniotic fluid volume if concerns arise.
- Discussion of birth plan: Review preferences for pain management, delivery location, and support people.
If you’re experiencing decreased fetal movements, your provider may request a non‑stress test (NST) or biophysical profile (BPP) to assess well‑being.
How much weight should I gain and what is a healthy weight gain at 31 weeks pregnant?
Weight gain recommendations vary based on pre‑pregnancy BMI. The Institute of Medicine (IOM) suggests the following total gains for a singleton pregnancy:
- Underweight (BMI < 18.5): 28–40 lb (12.5–18 kg)
- Normal weight (BMI 18.5–24.9): 25–35 lb (11.5–16 kg)
- Overweight (BMI 25–29.9): 15–25 lb (7–11.5 kg)
- Obese (BMI ≥ 30): 11–20 lb (5–9 kg)
By 31 weeks, most women have gained roughly 70‑80 % of the total recommended weight. If you’re within the target range, continue a balanced diet and moderate activity. If you’re ahead or behind, discuss a personalized plan with your provider—rapid weight gain can increase the risk of gestational diabetes and hypertension, while insufficient gain may affect fetal growth.
Warning signs and when to call the doctor at 31 weeks pregnant
While many symptoms are normal, certain signs warrant immediate medical attention. Red‑flag symptoms include:
- Vaginal bleeding heavier than spotting
- Severe abdominal pain or cramping that doesn’t subside
- Sudden swelling of face or hands (possible preeclampsia)
- Persistent headaches, vision changes, or upper‑right abdominal pain
- Decrease in fetal movements (less than 10 kicks in 2 hours)
- Leakage of fluid (possible rupture of membranes)
If you notice any of these, call your OB‑GYN or go to the nearest emergency department. For less urgent concerns—like mild swelling or occasional heartburn—schedule a routine visit or call your provider’s office during business hours.
Preparing for labor and creating a birth plan at 31 weeks pregnant
Now is an ideal time to fine‑tune your birth plan and gather the essentials you’ll need when the big day arrives.
Key components of a birth plan
- Labor environment: Preference for lighting, music, and room temperature.
- Pain management: Options such as epidural, nitrous oxide, IV pain meds, or natural techniques (breathing, water immersion).
- Support team: Who will be present—partner, doula, family member.
- Delivery preferences: Vaginal birth after cesarean (VBAC) considerations, position for pushing, use of forceps or vacuum.
- Newborn care: Immediate skin‑to‑skin contact, delayed cord clamping, breastfeeding initiation.
Hospital bag checklist for 31 weeks pregnant
Pack your bag by the end of this month so you’re ready for any early arrival. Many women find it helpful to keep the bag in the car or at a trusted friend’s house.
Safe exercises for 31 weeks pregnant
Staying active supports circulation, reduces back pain, and can improve mood. The American College of Obstetricians and Gynecologists (ACOG) recommends at least 150 minutes of moderate‑intensity aerobic activity per week, provided there are no contraindications.
Safe options include:
- Walking: Low‑impact, easy to modulate intensity.
- Prenatal yoga: Focuses on flexibility and breathing.
- Swimming or water aerobics: Relieves joint pressure.
- Stationary cycling: Keeps heart rate steady without risk of falls.
Avoid contact sports, deep squats, or any activity with a high risk of falling. If you’ve never exercised before, start with short 10‑minute sessions and gradually increase.
Travel guidelines for 31 weeks pregnant
Most airlines allow travel up to 36 weeks for uncomplicated pregnancies, but it’s wise to check the carrier’s specific policy. Bring your prenatal records, stay hydrated, and move your legs every hour to reduce clot risk.
Driving is safe as long as you use a seat belt correctly—low‑back portion under the belly and shoulder strap between the breasts. If you’re planning a long car trip, schedule stops every 1‑2 hours to stretch.
Sex during pregnancy at 31 weeks
For most women with a normal pregnancy, sex remains safe up to labor. The amniotic sac and strong uterine muscles protect the baby, and the cervix stays closed. However, avoid intercourse if you have:
- Placenta previa or low‑lying placenta
- Preterm labor signs
- Vaginal bleeding or discharge
- Infections like herpes or STIs
Communicate openly with your partner about comfort levels. Using pillows for support and choosing positions that reduce abdominal pressure can make the experience more enjoyable.
How to reduce swelling at 31 weeks pregnant
Swelling, or edema, is common because increased blood volume and pressure on veins from the uterus slows return flow from the lower body. Strategies to keep it in check:
- Elevation: Prop your feet on a stool while sitting.
- Compression stockings: Graduated compression helps venous return.
- Hydration: Paradoxically, drinking more water reduces fluid retention.
- Limit sodium: Avoid overly salty snacks and processed foods.
- Gentle movement: Short walks or ankle circles every hour.
If swelling suddenly becomes severe or is accompanied by headaches, visual changes, or protein in the urine, seek medical care promptly as it may signal preeclampsia.
Myth vs. fact
Myth: “You can’t exercise after the first trimester.”
Fact: Moderate, low‑impact exercise is recommended throughout pregnancy, including the third trimester, unless your provider advises otherwise.
Myth: “All seafood is dangerous for the baby.”
Fact: Low‑mercury fish such as salmon, sardines, and trout provide essential omega‑3s and are safe when cooked properly.
Myth: “If you feel the baby move less, it always means trouble.”
Fact: Fetal movement can vary day to day; however, a noticeable decrease warrants a prompt check‑in with your provider.
Key takeaways
- Your baby at 31 weeks is about the size of a cantaloupe, weighing ~3 lb 5 oz.
- Common symptoms include back pain, leg cramps, swelling, and heartburn—most can be eased with simple lifestyle tweaks.
- Follow a balanced diet rich in protein, calcium, iron, and omega‑3s; avoid raw/under‑cooked foods and high‑mercury fish.
- Safe exercises like walking, prenatal yoga, and swimming keep you active and may reduce discomfort.
- Regular prenatal visits, blood pressure checks, and a planned GBS screen keep both you and baby safe.
- Know red‑flag signs—bleeding, severe pain, sudden swelling, or reduced fetal movements—and call your provider immediately.
- Start your birth plan now and pack a hospital bag with essentials to feel prepared.
Frequently asked questions
How big is my baby at 31 weeks pregnant?
At 31 weeks, the average baby weighs about 3 lb 5 oz (1.5 kg) and measures roughly 16 inches (41 cm) long—similar in size to a cantaloupe. Individual size can vary, but most fetuses are within a few ounces of this average.
What are the signs of preterm labor at 31 weeks?
Watch for regular contractions (every 5‑10 minutes), a sudden increase in vaginal discharge, pelvic pressure, or low‑back pain that doesn’t ease with rest. If any of these occur, contact your obstetrician right away.
Can I still have sex at 31 weeks pregnant?
Yes, if you have an uncomplicated pregnancy and no medical contraindications like placenta previa or preterm labor signs. Use comfortable positions and listen to your body—stop if you feel pain or discomfort.
What should I pack in my hospital bag at 31 weeks?
Essential items include a comfortable robe, slip‑on shoes, toiletries, phone charger, insurance documents, a going‑home outfit for baby, snacks, and a copy of your birth plan. Pack the bag by the end of the month so you’re ready for an early arrival.
Is it safe to travel by plane at 31 weeks pregnant?
Most airlines allow travel up to 36 weeks for uncomplicated pregnancies. Bring your prenatal records, stay hydrated, and move your legs every hour. If you have a high‑risk pregnancy, check with your provider before booking.
What are the most common discomforts at 31 weeks pregnant?
Backaches, leg cramps, swelling in the ankles and hands, shortness of breath, frequent urination, heartburn, and Braxton‑Hill contractions are typical. Gentle stretching, compression socks, and staying hydrated can help alleviate many of these symptoms.
How can I reduce swelling at 31 weeks pregnant?
Elevate your feet, wear compression stockings, drink plenty of water, limit sodium, and move regularly. Sudden or severe swelling, especially with headaches or vision changes, should be evaluated promptly for preeclampsia.
When to see a doctor or specialist
If you notice any of the following, contact your OB‑GYN or go to the nearest emergency department immediately:
- Vaginal bleeding heavier than spotting
- Sharp, persistent abdominal or pelvic pain
- Sudden swelling of face, hands, or severe edema
- Persistent headaches, vision changes, or upper‑right abdominal pain
- Decrease in fetal movements (fewer than 10 kicks in 2 hours)
- Leakage of fluid (possible rupture of membranes)
This article is for informational purposes only and does not replace personalized medical advice. Always discuss any concerns or new symptoms with your healthcare provider.
References
- American College of Obstetricians and Gynecologists (ACOG). “Routine Prenatal Care.” 2023.
- Mayo Clinic. “Third Trimester Pregnancy: What to Expect.” Updated 2024.
- National Institute of Child Health and Human Development (NICHD). “Fetal Development: 31 Weeks.” 2022.
- Academy of Nutrition and Dietetics. “Nutrition During Pregnancy.” 2023.
- American Heart Association (AHA). “Physical Activity and Pregnancy.” 2022.
- U.S. Food and Drug Administration (FDA). “Pregnancy and Medication Safety.” 2023.
- World Health Organization (WHO). “Guidelines on Antenatal Care.” 2022.
- Institute of Medicine (IOM). “Weight Gain During Pregnancy.” 2009.
- National Library of Medicine (PubMed). “Magnesium Supplementation for Leg Cramps in Pregnancy.” 2021.
