At 33 weeks pregnant you are about 7 1/2 months along, in the third trimester, with about 7 weeks to go until your estimated due date.
At 33 weeks pregnant your baby is mostly built and is now busy gaining weight, and your to-do list is getting real: a car seat, a hospital bag, a pediatrician and two vaccine windows that are open right now.
This guide covers development, size, symptoms, appointments, sleep and the signs that mean you should call. Every clinical detail was read in October 2026 on the primary sources named in the text.
Key Takeaways
33 weeks pregnant is about 7 1/2 months, or 31 weeks after conception (Mayo Clinic), with about 7 weeks to go.
Mayo Clinic says the bones are hardening but the skull stays flexible and soft. Nemours KidsHealth says the lungs are almost completely matured.
Mayo Clinic puts a baby at about 3 3/4 pounds at week 32 and more than 4 1/2 pounds at week 34.
The CDC’s Tdap window runs from week 27 through 36 and its RSV vaccine window from week 32 through 36, during September to January.
Call right away for regular tightening, leaking fluid, bleeding, a severe headache, vision changes or a baby who is moving less.
Table of Contents
33 Weeks Pregnant at a Glance
Quick Answer
At 33 weeks pregnant you are about 7 1/2 months along, in your 8th month, with about 7 weeks to go. You are in the third trimester by every definition we checked. Mayo Clinic says your baby’s bones are hardening while the skull stays soft, and the CDC’s Tdap and RSV vaccine windows are both open.
33 weeks pregnant
What to know
Trimester
Third trimester on every definition we checked (ACOG via UPMC, MedlinePlus, Office on Women’s Health). See the table below.
Month
About 7 1/2 months, so you are in your 8th month. This counts 4 weeks and a few days per month. Months are a convention, not a medical unit.
Weeks to go
About 7 (40 minus 33, counted from the first day of your last menstrual period).
Baby’s size
Between Mayo Clinic’s week 32 figure (about 3 3/4 pounds) and its week 34 figure (more than 4 1/2 pounds).
Common symptoms
Shortness of breath, heartburn, swelling of the ankles and fingers, Braxton Hicks contractions, trouble sleeping.
This week’s care focus
Tdap and RSV vaccines if not done yet (CDC), your baby’s movements, and your birth to-do list.
33 weeks pregnant: quick facts with sources.
How the weeks are counted. The Office on Women’s Health says pregnancy lasts about 40 weeks, counting from the first day of your last normal period (LMP), not from conception. That is why Mayo Clinic describes week 33 as 31 weeks after conception. If an early ultrasound changed your due date, go by your adjusted dates.
Which trimester is 33 weeks? Sources start the third trimester at different points, but week 33 is inside it on all of them:
Source
Third trimester
Where week 33 falls
ACOG, as reported by UPMC
Starts at the beginning of the 29th week (28 weeks, 0 days) and runs until delivery
Sixth week of the third trimester
MedlinePlus (NIH)
Week 28 through week 40
Third trimester
Office on Women’s Health
Week 29 to week 40
Fifth week of the third trimester
Trimester definitions differ by source, so all three are printed.
Your Baby’s Development at 33 Weeks
Mayo Clinic says that by week 31 your baby has finished most major development, and that it is now time to gain weight quickly.
Source and timing
What it says is happening
Mayo Clinic, week 33 (31 weeks after conception)
The pupils can change size in response to light. The bones are hardening, but the skull is still flexible and soft.
Nemours KidsHealth, week 33
The lungs are almost completely matured. Like a newborn, the baby sleeps much of the time, including REM sleep. Fat keeps building for protection and warmth.
Office on Women’s Health, week 32
The bones are fully formed but still soft. The eyes can open, close and sense light. The baby is gaining about one half pound a week.
Mayo Clinic, week 32
Toenails are visible. Lanugo, the soft, downy body hair, starts to fall off.
Mayo Clinic, week 34
The fingernails have reached the fingertips.
Mayo Clinic, week 35
The baby fills most of the space in the amniotic sac and has less room to move, though you will probably still feel lots of stretches, rolls and wiggles.
Fetal development around week 33, by source.
Weight gain is the big job now. Nemours KidsHealth says babies gain a good deal of their weight in the final few weeks before birth.
How Big Is Your Baby at 33 Weeks?
None of the primary sources we read gives a week 33 measurement, so here are the closest figures on either side, printed as each source wrote them.
Source
Week
Length
Weight
Mayo Clinic
32
11 inches (280 mm), crown to rump
About 3 3/4 pounds (1,700 g)
Office on Women’s Health
32
About 15 to 17 inches
About 4 to 4 1/2 pounds
Mayo Clinic
34
Nearly 12 inches (300 mm), crown to rump
More than 4 1/2 pounds (2,100 g)
Office on Women’s Health
36
About 16 to 19 inches
About 6 to 6 1/2 pounds
Baby size near 33 weeks, by source.
Mayo Clinic measures crown to rump, which leaves out the legs, so its lengths are shorter. The Office on Women’s Health does not say how it measures. A baby at 33 weeks sits somewhere between the week 32 and week 34 rows. Healthy babies vary.
A 33 week ultrasound? MedlinePlus says there are no routine lab tests or ultrasounds for every pregnant woman in the third trimester other than the group B strep test. UPMC says a scan may be ordered for concerns about growth, fluid or the placenta.
33 Weeks Pregnant Symptoms
The Office on Women’s Health and UPMC list these third trimester changes. You may have many or few.
Shortness of breath: UPMC says to get medical help immediately if shortness of breath is sudden or severe.
Heartburn: UPMC says eating smaller meals throughout the day can help.
Swelling: of the ankles, fingers and face (Office on Women’s Health). UPMC says to seek treatment for sudden or extreme swelling, which can be a sign of preeclampsia.
Leaking colostrum: the Office on Women’s Health says tender breasts may leak a watery pre-milk called colostrum.
Braxton Hicks or preterm labor? Labor before 37 weeks is preterm labor (March of Dimes). Irregular tightenings that ease with rest or movement fit Braxton Hicks (UPMC). Regular or frequent ones are a reason to call right away (March of Dimes).
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Your bump is big now. At each visit your provider measures your abdomen to see whether your baby is growing as expected and checks your weight, blood pressure and the baby’s position (MedlinePlus).
Belly button: the Office on Women’s Health says it may stick out.
Dropping: the baby moving lower in your abdomen is on the Office on Women’s Health third trimester list. UPMC says it can happen around week 36, when the head may drop lower into your pelvis to prepare for birth.
Appetite: UPMC reports that ACOG puts your extra need at about 450 calories a day in the third trimester.
Your baby’s movements. UPMC says forceful kicks may feel less frequent as space runs out, but you will still feel movements and stretches. MedlinePlus says you will notice periods of activity and inactivity.
Kick counts. Cleveland Clinic says kick counting becomes more important in the third trimester and reports that ACOG recommends checking whether you feel 10 kicks, flutters, swishes or rolls within two hours. Lie on your left side or sit with your feet up and count to 10. If you have not felt 10 movements after two hours, or movement slows down or feels very different, call your provider. Ask when your provider wants you to start counting.
Prenatal Care, Tests and Appointments Around Week 33
What
Window
Source
Prenatal visits
Every 2 weeks until week 36, then weekly
MedlinePlus
Tdap (whooping cough) vaccine
During the 27th through 36th week of each pregnancy
CDC
RSV vaccine
You can choose it during weeks 32 through 36, during September to January
CDC
Flu vaccine
By the end of October
CDC
Group B strep test
A few weeks before your due date (coming up)
MedlinePlus
Glucose screening
Done in the third trimester if it was not done earlier
UPMC
Tests and vaccines near week 33, as read in October 2026.
At your visits MedlinePlus says your provider may also discuss the timing of delivery and possible modes of delivery, and may do a pelvic exam to see whether your cervix is dilating. March of Dimes notes that providers check whether the cervix is thinning and opening, which is called effacement and dilation.
Vaccines. The windows above are from the CDC page as read in October 2026 (updated October 7, 2026). Guidance changes, so confirm Tdap, RSV, flu, COVID-19 and any other vaccines with your own provider.
Group B strep. UPMC explains that a positive swab result means you get antibiotics during birth. It is coming soon, not this week.
What to Do This Week: A Simple Checklist
Ask about Tdap and the RSV vaccine if you have not had them, and confirm timing with your provider.
Choose a pediatrician for your baby (UPMC).
Install your newborn’s car seat (UPMC), following the seat and vehicle manuals.
Pack your hospital bag (UPMC), including a going-home outfit for the baby.
Write your birth plan if you have not already, and discuss it with your provider (UPMC).
If you have other children, arrange childcare for when you go into labor (UPMC).
Save your provider’s after-hours number and learn the warning signs at the end of this guide.
Pace your nesting energy: short bursts, no ladders, and plenty of rest.
Pain relief options. Nemours KidsHealth names breathing techniques, pain relief medicines given by injection, and epidurals, and suggests discussing your choices with your provider soon.
Sleep at 33 Weeks Pregnant
Trouble sleeping is on the Office on Women’s Health third trimester list: breathlessness, heartburn, bathroom trips and a big belly all compete with rest.
Sleep position. UPMC says that as your belly grows, you should avoid sleeping on your back, because the weight of your uterus may compress a blood vessel that supplies blood to your uterus, which could make you feel dizzy and reduce blood flow to your baby. UPMC adds that if you roll onto your back at night, the discomfort usually wakes you, so just roll back to your side.
Use a body pillow: UPMC suggests one for comfort. Our guide on how to use a pregnancy pillow walks through the options.
Breathe and move: UPMC suggests deep breathing to help you fall asleep and walking during the day.
Ask before any sleep aid: check with your provider before taking any sleep medicine or supplement. Read can you take melatonin while pregnant first.
For Partners: How to Help at 33 Weeks
Own one item on the checklist above from start to finish, such as the car seat installation or choosing the pediatrician.
Learn the warning signs below so you can make the call if she is unsure.
Take on jobs that strain a sore back, like laundry baskets and grocery bags.
Talk and read to the bump. Nemours KidsHealth says the baby can listen at this stage.
Looking Ahead: What Comes Next
Weeks 34 and 35: fingernails reach the fingertips, and the baby fills most of the amniotic sac (Mayo Clinic).
Week 36: the CDC’s Tdap and RSV windows close at the end of week 36. MedlinePlus says visits become weekly after week 36. UPMC says the baby’s head may drop lower into your pelvis around now.
Week 37: labor is no longer preterm (March of Dimes).
Signs of preterm labor. March of Dimes says that before 37 weeks you may be in preterm labor if you have any of these, and to call your provider right away if you have even one:
Regular or frequent contractions that make your belly tighten like a fist.
A change in your vaginal discharge (watery, mucus or bloody), or more discharge than usual.
Pressure in your pelvis or lower belly, like your baby is pushing down.
A constant low, dull backache.
Belly cramps, with or without diarrhea.
Your water breaks.
Seek care right away. UPMC and MedlinePlus list these warning signs for the third trimester:
A decrease in your baby’s movement.
Any vaginal bleeding.
A severe headache that does not go away, or changes or blind spots in your eyesight.
Sudden or severe swelling of your hands and face, or significant swelling with weight gain.
Chest pain, a fast heart rate or difficulty breathing.
A fever above 100.4 F, chills, or pain when you pass urine.
Severe cramping, or regular, painful contractions.
Headache, vision changes and sudden swelling can be signs of preeclampsia. UPMC also says thoughts of harming yourself warrant immediate help.
If you cannot reach your provider quickly, go to labor and delivery or the nearest emergency room. If you have severe chest pain, severe trouble breathing, a seizure or heavy bleeding, call 911. When you call, say how many weeks pregnant you are. This article is general education, not medical advice.
Frequently Asked Questions
How many months is 33 weeks pregnant?
About 7 1/2 months, which puts you in your 8th month, counting 4 weeks and a few days per month. You have about 7 weeks to go. Months are only a convention, which is why your provider counts in weeks.
How big is a baby at 33 weeks pregnant?
Our sources give no week 33 figure. Mayo Clinic says about 3 3/4 pounds and 11 inches crown to rump at week 32, and more than 4 1/2 pounds and nearly 12 inches crown to rump at week 34. Healthy babies vary.
Is it normal to have Braxton Hicks contractions at 33 weeks?
Yes, UPMC lists them as a common third trimester symptom: they are not regular and go away with rest or a change of position. Regular or frequent contractions before 37 weeks can signal preterm labor, so call your provider right away.
How often should my baby move at 33 weeks?
Cleveland Clinic says 10 movements in one or two hours is considered typical and reports that ACOG recommends checking for 10 within two hours. If movement slows, feels very different, or you do not reach 10 in two hours, call your provider.
What if I go into labor at 33 weeks?
Labor before 37 weeks is preterm labor. March of Dimes says to call your provider right away with even one sign, such as regular tightening, a change in discharge, pelvic pressure, a constant dull backache or your water breaking. Getting help quickly is the best thing you can do.
What position should I sleep in at 33 weeks pregnant?
Sleep on your side. UPMC says that as your belly grows you should avoid sleeping on your back, because the weight of your uterus may press on a blood vessel and reduce blood flow to your baby. A body pillow can help.
Calmer days, better nights.
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