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31 Weeks Pregnant: Baby Size, Symptoms and What to Do

Week 31 is in the third trimester, month 7 of pregnancy. Here's how big your baby is, what's developing, what you may feel and what to do this week.

Week 31 · 3rd trimester · month 7
About the size of a pineapple
about 16.1 in (41 cm) · 3.8 lb (1,710 g) (head to heel)

Your baby this week

Your baby is very active and filling out nicely. Familiar voices, especially yours, are becoming recognizable.

At 31 weeks your baby is gaining weight quickly: birth weight is several times what it is at the start of the third trimester. All five senses are working, and your baby moves between sleep and wake more smoothly. With less room, movements can feel different: fewer big kicks and more stretching and squirming. The amount of movement shouldn't drop, though; if you feel less, call labor and delivery right away. For you, shortness of breath is common because your uterus presses on the diaphragm. Good posture and an extra pillow at night can help. Sudden breathlessness, chest pain or a racing heart needs urgent care.

By the numbers

Week 31 covers days 217 to 223 counted from the first day of your last period, which is 78% of a 40-week pregnancy. About 63 days remain until a 40-week due date. Since last week, an average baby gains about 6.7 oz (190 g). By date of conception, your baby is about 29 weeks old.

Pregnancy is dated from the first day of your last period, so conception happens around week 2. Your due date is 280 days (40 weeks) from that day, and an early ultrasound may adjust it.

Your body

With less room for your lungs, stairs can leave you winded. Tell your provider about intense itching, especially on your palms or soles or at night.

Tests and to-dos this week

Start a list for your hospital bag: ID, insurance card, comfortable clothes and a going-home outfit for your baby.

  • Tdap (whooping cough) vaccine · weeks 27–36 · vaccine

    Recommended during each pregnancy, preferably early in this window.

Coming up: RSV vaccine (September–January) (from week 32). Full prenatal visit schedule

Tips for the third trimester

  • From 28 weeks, go to sleep on your side; if you wake on your back, just roll over.
  • Pack your hospital bag and agree with your provider on when to head in.
  • Call right away, even at night, if your baby moves less or differently.
  • Know the signs of labor: regular, strengthening contractions, your water breaking or a bloody show.

Call your provider or labor and delivery right away if you have:

  • your baby is moving less or differently than usual
  • your water breaks, especially if the fluid is green, brown or smells bad
  • bright red bleeding or constant, severe belly pain
  • a severe headache, vision changes, pain under the ribs or sudden swelling
  • intense itching, especially on the palms and soles

In an emergency, call 911.

Last week and next week

Last week (30): Your baby's eyes can now focus.

Next week (32): Your baby is fully formed and mostly gaining weight now.

Frequently asked questions

How big is the baby at 31 weeks?

About the size of a pineapple: about 16.1 in (41 cm) · 3.8 lb (1,710 g), measured head to heel. These are rounded averages, and every baby grows at their own pace.

How many months is 31 weeks pregnant?

31 weeks is in month 7 and the third trimester. About 9 weeks (63 days) remain until a 40-week due date. Months are approximate; providers count weeks and days.

Do baby movements change in the third trimester?

They can feel different as space gets tight, with more squirming and fewer big kicks, but they shouldn't slow down right up to birth. If they do, call labor and delivery right away.

What's the next test or appointment after week 31?

Next up: RSV vaccine (September–January), from week 32. Your provider may schedule things differently depending on your health and local practice.

Sources

Last reviewed: November 14, 2026 · Kitpebble editorial team

This page is for general information. It isn't medical advice or a diagnosis and doesn't replace your OB-GYN or midwife. Sizes are rounded averages. Our editorial policy

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