Week 33 of Pregnancy: Your Baby Is the Size of a Celery

TL;DR

• Your baby is about 43.7 cm long — roughly the size of a celery bunch
• Bones are hardening throughout their body, but the skull stays flexible for birth
• You may be dealing with increased pelvic pressure, swelling, and difficulty finding a comfortable position
• Install your car seat and have it inspected — one less thing to worry about later

Your Baby This Week

Your baby's skeleton is going through an important transformation this week. Bones throughout their body are hardening and strengthening as calcium deposits increase. By now, about 250 milligrams of calcium are being deposited in your baby's skeleton every day — which is why your own calcium intake is so important right now.

But here's a clever bit of design: the bones of your baby's skull will remain soft and flexible, connected by gaps called fontanelles. These soft spots allow the skull to compress slightly during birth, making it possible for your baby's head to navigate the birth canal. The fontanelles won't fully close until your baby is about 18 months old, giving the brain plenty of room to continue its rapid growth after birth.

At 43.7 cm and about 4.2 pounds, your baby is putting on roughly half a pound per week now. Their immune system is continuing to develop, with antibodies passing from you through the placenta. Your baby is also practicing sucking and swallowing — essential skills for feeding after birth.

Your baby's sleep patterns are becoming more distinct. You might notice periods of quiet (when they're sleeping) and periods of intense activity. Many parents report that their baby seems most active in the evening, right when they're trying to wind down. Your baby's awake time might not align with yours — but this gives you a preview of those early newborn days.

Your Body This Week

Pelvic pressure is likely increasing as your baby continues to grow and settle lower. Walking might feel uncomfortable, and you might notice a waddle creeping into your gait. This is your body's way of accommodating the extra weight and shifted center of gravity. Wide-legged sitting, gentle stretching, and pelvic tilts can help ease discomfort.

Swelling in your feet and ankles may be more noticeable, especially at the end of the day or in warm weather. Your body is retaining more fluid, and the weight of your uterus can compress blood vessels that return fluid from your legs. Elevating your feet, wearing comfortable shoes, and staying hydrated all help. Remember: sudden or severe swelling, especially in your face or hands, warrants a call to your provider.

You might also be experiencing carpal tunnel symptoms — tingling, numbness, or pain in your hands and wrists. Fluid retention can put pressure on the nerves in your wrist, causing these sensations. Wrist splints, especially at night, can provide relief. For most people, these symptoms resolve after delivery.

Sleep continues to be challenging. Between the physical discomfort, the mental to-do list running through your head, and your baby's nighttime dance parties, getting solid rest requires strategy. Keep your room cool and dark, establish a wind-down routine, and don't feel guilty about napping during the day when you can.

Common Questions at Week 33

When should I install the car seat?

Now is a great time. Install the car seat in the back seat of your car, rear-facing, and then have it inspected by a certified car seat technician. Many fire stations, police departments, and hospitals offer free car seat inspections. Getting this done now means it's one less thing to scramble for when labor starts. The last thing you want is to be figuring out a car seat harness while a newborn is waiting.

What are fontanelles and are they dangerous?

Fontanelles are the soft spots on your baby's skull where the bones haven't fused together yet. They serve two purposes: they allow the skull to compress during birth, and they give the brain room to grow rapidly during the first year and a half of life. They're covered by a tough membrane, so gentle touching during baths or hair washing won't hurt your baby. The posterior fontanelle usually closes by 2-3 months, and the anterior (top) fontanelle by 18 months.

Is it normal to feel like I can't take a deep breath?

Yes. Your uterus is pushing up against your diaphragm, and there's simply less room for your lungs. Good posture helps, and you may get some relief in the coming weeks as your baby drops lower. If you're experiencing sudden difficulty breathing, chest pain, or a rapid heart rate, contact your provider — but the general feeling of not being able to breathe deeply is a normal third trimester experience.

How much longer until my baby could survive if born early?

Babies born at 33 weeks have an excellent chance of survival — over 98% — though they would likely need time in the NICU to develop their lungs and feeding skills. Every day in the womb counts, and the next few weeks are especially important for lung maturation and weight gain. But it's reassuring to know that if your baby arrived early, they would be well-supported by medical teams.

This Week's Tip

Install the car seat and have it inspected. This might seem like something you can put off, but getting it done now is a gift to your future self. Choose a rear-facing car seat, install it in the center of the back seat if possible, and then find a local inspection station (your hospital, fire station, or police department can usually help). Car seat installation is one of those things that seems straightforward until you're actually doing it — and having a professional check your work gives you real peace of mind.

Sources

• American College of Obstetricians and Gynecologists (ACOG) — Third Trimester
• Mayo Clinic — Fetal Development: The Third Trimester

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