33 Weeks Pregnant: The Week You Give Your Baby Their First Shield

Last week, your baby was getting into position for the big day. This week, you begin giving them something extraordinary, a gift only you can give. Your own hard-won immunity.

Welcome to week thirty-three. While your baby keeps growing and getting ready, your body is quietly arming them with a lifetime of your defences, a shield to carry them safely into a world they have not yet met. Let me show you.

You are giving your baby your immunity

This week, your body begins one of the most generous things it will ever do. It starts handing your baby your own immunity.

Floating in your blood are antibodies, tiny defenders your body has built up over your entire life, from every cold you have shrugged off and every illness you have ever recovered from. And now, through the placenta, those antibodies are crossing over into your baby.

This sharing has been trickling along quietly for a while, but in these final weeks it ramps right up. So much so that by the time your baby is born, they will carry a whole arsenal of your defences in their tiny body, sometimes even more than you have yourself. A ready-made shield, passed straight from you.

Why this gift matters so much

Here is why this is such a precious thing. When your baby is born, their own immune system is still brand new and learning. For the first few months of life, while it slowly finds its feet, your baby leans almost entirely on the protection you are giving them right now.

It is a borrowed immunity, a head start, holding them safe through those tender early weeks until their own defences grow strong enough to take over.

And once your baby arrives, your body simply carries on giving this protection through your milk. But more on that wonder in the weeks to come.

How big is my baby at 33 weeks?

Around forty-three to forty-four centimetres now, head to heel, and over two kilograms. Your baby is rounding out, their skin smooth and pink, and they are snug in a womb that is just about as full of fluid as it will ever get.

Strong, well-cushioned, and busy stockpiling everything they need for the world.

What is happening in my body?

Your bump is big and round now, and likely the firm, high focus of your whole body.

You may be feeling breathless, struggling with heartburn or indigestion, and finding sleep harder to come by, between needing the loo, an active baby, and the simple challenge of getting comfortable. Swollen feet and ankles are common too. Try to put your feet up when you can, sip water through the day, and sleep on your side with a pillow between your knees if it helps. And if you ever notice sudden or severe swelling, a bad headache, or changes to your vision, contact your midwife promptly, just to be safe.

From Courtney. I have looked after a lot of babies, and this is one of the things about mothers that never stops moving me. Long before you can pack a hospital bag or settle on a name, your body is already defending your baby, handing over the immunity you have spent your whole life building. Every bug you have ever fought off, quietly written into the shield you are giving them now. And it does not stop at birth. It carries them through those tender first months, when they are far too new for the world to be safe on their own. You are, in the most literal way, your baby's first line of defence, and you have been all along. That is not nothing, mama. That is everything.

The one thing to do this week

This week, with your body quietly doing the extraordinary work of protecting your baby, the one thing I would ask is this. Be as gentle with yourself as your body is being with your baby.

You are carrying a great deal right now, in every sense. So rest without guilt. Eat what feels good and steadies you. Say no to the things that can wait. Let people help you, and let some jobs simply go undone. Your only real task in these final weeks is to look after the two of you, and you are already doing it, beautifully, just by being here.

Feet up, mama. You have more than earned it.

Coming up in week thirty-four

Next week, your baby starts rehearsing the most important skill of their first day. How to feed. They practise the delicate dance of sucking, swallowing, and breathing, all in the right order, so that when they are finally placed in your arms, they will know just what to do.

Week thirty-four is where your baby gets ready for their very first feed. I will see you there.

Written by Courtney Garland, NICU nurse, lactation consultant and mother of four, and founder of The Mama Years. This is here to inform and reassure you. It is not a substitute for medical advice, so always follow the guidance of your own doctor or midwife.

The Mama Years. 2026.

References

Cleveland Clinic. (2023). Fetal development: Stages of growth. https://my.clevelandclinic.org/health/articles/7247-fetal-development-stages-of-growth

Mayo Clinic. (2025). Fetal development: The third trimester. https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/fetal-development/art-20045997

Merck Manual. (2024). Stages of fetal development (Consumer Version). https://www.merckmanuals.com/home/women-s-health-issues/normal-pregnancy/stages-of-fetal-development

Palmeira, P., Quinello, C., Silveira-Lessa, A. L., Zago, C. A., & Carneiro-Sampaio, M. (2012). IgG placental transfer in healthy and pathological pregnancies. Clinical and Developmental Immunology, 2012, 985646. https://doi.org/10.1155/2012/985646

The Mama Years is written by Courtney Garland, a NICU registered nurse and IBCLC lactation consultant, against the research. When the science is genuinely unsettled, she says so instead of guessing. Nothing here replaces the advice of the clinician looking after you.