Pregnancy is one of the most extraordinary things a body can do. Over the course of nine months, you'll grow, shift, expand, and soften in ways that surprise even the most body-aware among us. And through all of it, the one thing pressed against your skin from morning to night? Your bra.

At Perk by Kate, we've spent over a decade in the fitting room with real women at every stage of pregnancy and postpartum. We know that a bra that fits beautifully at 8 weeks may feel suffocating by week 20 — and that the right support can genuinely change how you feel in your body on a hard day. This guide walks you through what to expect, trimester by trimester, how to measure yourself accurately as your body changes, and which PBK styles are designed to carry you through every stage with both comfort and a little grace.

Because you deserve to feel like a goddess — bump and all.

First Trimester Weeks 1-13: Tender, swollen & sensitive

For many women, breast tenderness is the very first sign that something is changing. Even before a bump is visible, your breasts are already preparing, increasing in glandular tissue and blood flow. The result: a fullness that can range from mildly uncomfortable to achingly sensitive to touch.

This is not the time for underwires. Any bra with a rigid frame can press into tender, developing breast tissue, which may cause discomfort. There is no strong clinical evidence that underwire bras interfere with milk duct development but many women prefer wire free styles during pregnancy for comfort alone.

You may only go up half a cup to a full cup size in these early weeks so it is tempting to hold off on new bras. However, if you are already finding your usual bra fitting tight on the band or uncomfortable against the cup, it is time to switch or get a bra extender. Comfort is not a luxury during pregnancy, it is a necessity. 

PBK pick for your first trimester:

Mia Convertible Soft Bra 

Our beloved best-seller in a sustainable milk silk and cotton blend. No wires, no fuss, just gentle support that moves with you. The convertible straps mean you can adjust the fit as your body changes and the soft fabric is kind to even the most tender skin. Customers come back to this one pregnancy after pregnancy.

Second Trimester Weeks 14-27- Growing, changing & finding your rhythm 

The second trimester is often called the ‘golden’ one as the fatigue and nausea of early pregnancy lifts, energy returns and your bump becomes a beautiful reality. Your body is doing the most. Your breasts are continuing to grow and change and many women notice the underbust area widening as the ribcage expands.

Between weeks 20-36, every body will be different, some women notice rapid changes, other less so. Some women find their old maternity bras still work well, whereas others find them becoming tights and restrictive week after week. Pay attention to the signs that your bra is no longer fitting correctly: red marks on your skin, straps slipping off, bra riding up at the back or cups gaping or overflowing.

Re-measuring during this trimester is wise as a well-fitting bra is important. It should feel like a supportive second skin and you should not have to tug on it at all or adjust it throughout the day. If you are, it is time to change to a comfortable size that honours your changing body.

This is also a beautiful time to invest in something that makes you feel genuinely lovely. Your body is doing extraordinary things and your lingerie should honour that.

PBK picks for your second trimester:

Harper Full-Cup Padded Bralette

Designed with your curves in mind, Harper combines feminine elegance with everyday durability. The full-cup construction offers meaningful coverage and support as your bust grows, while the padded cups and wide band distribute weight comfortably. It is the bra you will reach for on days when you want to feel put together and supported.

Third Trimester Weeks 28-40 - Almost there: Preparing for baby & beyond

By week 36, your bra size may offer a general starting point for what you might need postpartum for nursing, but breast size can change significantly when milk comes in (usually 2-5 days after birth). This is the right moment to invest in maternity and nursing bras that will serve you through birth, early postpartum and your feeding journey because in those first hazy newborn weeks, the last thing you want to think about is lingerie shopping.

The third trimester often brings a final breast growth and the underbust may expand further as your uterus pushes upwards. You may also begin to experience colostrum leaks, some women do and some don't, and nursing pads will become your best friend. Working hand in hand with a bra that has a nursing clip or sling means you do not need to remove it with each feed.

Night bras or sleep bralettes are worth considering now too. Many women in late pregnancy and early postpartum find sleeping braless uncomfortable, particularly once milk comes in. A soft, wirefree sleep bralette can make those middle of the night feeds more manageable.

PBK picks for your third trimester:

Do-It-All Maternity Nursing Soft Bra 

Endearing Maternity Nursing Padded Bralette 

The Do-It-All is your practical hero, it is wirefree with a nursing clasp and sling for easy access and base cup ruching that accommodates your changing shape. The Endearing Maternity Nursing Padded Bralette brings the beauty in its stunning rose lace motif,  full coverage cups and a soft elastic underband that is as gentle as it is supportive. Together, they cover everything from a Monday morning feed to a maternity shoot moment.

After baby- the fourth trimester

The “fourth trimester”, those first twelve weeks after birth, deserves its own conversation. Your body is recovering, hormones are regulating and if you are breastfeeding, your breasts are doing something entirely new. Engorgement in the early days can increase cup size significantly. For many women, this settles within a few weeks as milk supply regulates, but some find their postpartum breast size remains larger than during pregnancy.

Ease and access are everything in the newborn post baby phase. You do not want complicated closures when you are feeding in the dark at 3am. Nursing clips, drop-down cups and front zip styles are not just for conveniences but also to preserve your sanity. Adding on, if you are pumping, a hands-free pumping bra is genuinely life-changing.

PBK pick for postpartum:

UPLIFT Hands-Free Cotton Pumping Bra

Removable convertible straps, a velcro back extender for a custom underbust fit and a front zip bust extender so you can define your fit as your body changes week by week. Hands-free pumping means you can actually eat, work or just breathe while you pump. Made from OEKO-TEX certified fabric, because what is closest to your skin and your body, should always be safe.

Every body is different.

Every fit should be too.

How to Measure Your Size:

Because pregnancy changes your shape so quickly, we don't recommend relying on a tape measure alone. Instead, try on bras in two adjacent cup sizes — the one that fits best without gaping or digging is your size right now. If you'd like to measure at home, here's how...

Step 1 — Band (Rib Cage)

Measure around your rib cage, right under your breasts, keeping the tape level and snug but not tight. Exhale normally. If the number falls between two sizes, size up — your rib cage will continue expanding through the second and third trimesters.

Step 2 — Bust (Over Fullest Part)

Measure around the fullest part of your breasts while standing, with the tape loose enough not to compress tissue. If your breasts are tender or you're later in pregnancy, also measure while sitting or leaning slightly forward — this catches side tissue that standing alone might miss.

Step 3 — Compare But Don't Obsess

Subtract your band measurement from your bust measurement. One inch = A cup, two inches = B cup, etc. However: during pregnancy, this calculation often underestimates cup size because breast shape changes. Many pregnant women need one cup size larger than the tape suggests.

Step 4 — The Real Test

The tape measure gives you a starting size. The real test is how the bra feels. Put the bra on the loosest hook. If the band rides up, it's too big. If the underwire (if any) sits on breast tissue instead of rib cage, or if the center gore floats instead of lying flat, go up a cup size. If you're between sizes, choose comfort over math.

Final note:

During pregnancy, we recommend measuring every 4–6 weeks, not because you're doing it wrong, but because your body isn't. If measuring feels frustrating or uncomfortable, skip it entirely, our fit specialists can help without a tape measure.

Whether you are weeks away from your due date or deep in the newborn haze, we are always here to help you find the right bra for any moment. You deserve to feel held, supported and genuinely beautiful at every stage of this extraordinary journey.