Pregnancy & Maternity Bras: How Your Size Changes | HauteFlair

HauteFlair EditorsUpdated August 202613 min readMaternity & Nursing Fit

Quick Answer

What is the difference between a maternity bra and a nursing bra?

A maternity bra, also called a pregnancy bra, is built to accommodate a body that is changing. A nursing bra is a maternity bra that also opens. Both have a wide soft band, several rows of hooks so the band can be let out and taken back in, stretch or seamed cups rather than moulded ones, wide adjustable straps, and usually no rigid wire. A nursing bra adds cup access for feeding, normally a drop-cup released by a clip at the top of the strap. So every nursing bra works as a maternity bra, while a maternity bra without cup access cannot be used for feeding. That asymmetry is why many people buy nursing bras from around 36 weeks and skip buying maternity-only bras for the third trimester. And the reason any of this is needed is that size does not drift gently upward. It moves through four distinct phases, the band changes before the cup, and the biggest jump is also the briefest.

Skip straight to shoppingBrowse maternity and nursing bras, bands 28 to 46 and cups A to K.

Shop Maternity & Nursing

Most advice on this treats pregnancy as one long gradual increase, which is why people buy six bras in month four and none of them fit by month nine.

The change happens in stages, each with a different shape, and knowing which stage you are in tells you what to buy and how much.

Maternity vs Nursing The Four Phases Why the Band Goes First Sizing at 36 Weeks What to Buy When Ask a Midwife FAQ

Quick Answer: The Short Version

Nursing bras do both jobs. Maternity bras do not open, so they only work before the birth.
The band changes first, because the ribcage expands. The cup follows later.
Measure at 36 weeks and buy one cup larger, for engorgement.
Four rows of hooks, so the band can take up slack as the ribcage settles back.
Never moulded cups. Volume changes within a single day; a fixed shape cannot follow it.
Two or three at a time, not a full set. Size keeps moving.
Re-measure every 6 to 8 weeks rather than waiting for a bra to stop fitting.

4distinct phases, each with a different shape of change.

36 wksis when to measure for nursing bras. The ribcage has mostly finished by then.

2-3bras per phase, not six. Size moves faster than a wardrobe can keep up.

Maternity Bra, Nursing Bra, or Both

The two terms get used interchangeably and describe overlapping but different garments. The difference is one feature, and it is worth understanding because it changes how many bras you need to buy.

	Maternity / pregnancy bra	Nursing bra
Wide soft band	Yes	Yes
Multiple hook rows	Yes	Yes
Stretch or seamed cups	Yes	Yes
Wire-free or flexible wire	Usually	Usually
Cup opens for feeding	No	Yes, via a clip
Usable before birth	Yes	Yes
Usable after birth	Only if not feeding	Yes

The practical consequence is straightforward. If you are early in pregnancy and want comfort now, a maternity bra is fine and often cheaper. If you are past about 36 weeks, buy nursing bras instead, because they do everything a maternity bra does and continue working afterwards. Buying maternity-only bras in the third trimester means buying twice.

Close-up of a nursing bra clip at the top of the strap, shown unfastened

The one feature that separates the two categories: a clip at the top of the strap releasing the cup. Worth testing one-handed before you buy, since that is how you will always be using it.

The Four Phases

Size does not increase steadily. It moves in stages, and each stage has a different character.

What Changes, and When

Phase 1 · first trimesterTenderness Arrives Before SizeOften the earliest physical change anyone notices, sometimes before a bump. Breasts become tender and may increase slightly, and the ribcage begins to expand. What most people need here is not a bigger bra but a softer one: no rigid wire, a wide band, and nothing pressing. One or two soft bras is plenty, because this phase does not last and buying more means buying for a body you will not have in three months.

Phase 2 · second and third trimesterThe Band Expands, Then the CupThe ribcage flares outward to make room, so band size increases first and often surprises people, since the bra feels tight around the body before it feels tight in the cup. Cup volume then increases through the third trimester. This is where four rows of hooks earn their place, letting one band cover a range rather than needing replacement. Expect to move up a band size, sometimes two.

Phase 3 · the first week after birthEngorgement: Biggest and BriefestWhen milk comes in, usually within the first week, cup volume increases sharply. It is the largest jump of the entire period and also the shortest, typically settling within days as feeding establishes. This is why bras bought before birth should allow a cup size for it rather than being sized to fit it. Buying to fit engorgement exactly leaves you with bras that are too big a fortnight later.

Phase 4 · established feeding and weaningIt Settles Somewhere NewOnce feeding establishes, size becomes more stable but still varies within a day, fuller before a feed and softer after. The ribcage gradually settles back, which is what the tighter hooks are for. After weaning, size usually lands somewhere new rather than returning precisely to where it started, and both band and cup may differ. That is normal, and it is worth being re-measured once things have been stable for a couple of months.

Bras of increasing size laid in a row showing how band and cup change across pregnancy

The progression laid out. What the row does not show is the timing: most of the band change happens before most of the cup change, and the sharpest increase of all lasts only a few days.

Ready to shop?

Maternity and Nursing Bras That Follow the Change

Wide bands, four-row closures, seamed cups and drop-cup access. Bands 28 to 46, cups A to K.

Shop Maternity & Nursing Find Your Size

Why the Band Changes Before the Cup

The ribcage itself expands during pregnancy. The lower ribs flare outward to make room as the uterus grows and lung capacity increases, and the band measurement grows with them. That is a skeletal change, and it happens whether or not breast volume has changed at all.

This explains an experience almost everyone has and few expect: a bra that feels tight around the body before it feels tight in the cup. The instinctive reading is that the whole bra has become too small, and the instinctive fix is to buy a bigger cup, which does not address the problem.

The correct response is the same as it is in any bra: adjust both together. Going up a band while keeping the same cup letter actually increases cup volume, because a cup letter is defined relative to its band. If you want the same volume on a bigger band, go up a band and down a cup letter. If you genuinely need more volume too, which you will later, go up both.

It also explains why hook rows matter so much here. A four-row closure gives roughly three inches of range, which is often enough to cover the entire band expansion of a pregnancy on one bra, and then to take the slack back up as the ribcage settles afterwards.

How to Size a Nursing Bra While Pregnant

Step 1

Measure at Around 36 Weeks

By the third trimester the ribcage has done most of its expanding, so a measurement taken around 36 weeks is a far more useful basis than one taken earlier. Measure the ribcage directly under the bust, snug and level, rounded to the nearest even number. Add nothing.

Step 2

Measure the Bust and Subtract

Measure around the fullest part of the bust, level all the way round and not pulled tight. Subtract the ribcage measurement. Each inch of difference is one cup letter: one inch an A, two a B, three a C, and so on.

Step 3

Add One Cup Size for Engorgement

Buy one cup larger than you measure. Milk coming in produces the largest increase of the whole period and it arrives fast, so a bra sized exactly to your 36-week measurement will be too small in the week you most need it to fit.

Step 4

Buy the Band to Fit Now, on the Loosest Hook

The band should be comfortable on the loosest hook at 36 weeks. As the ribcage settles back after birth, the tighter hooks take up the difference. This is the opposite of the usual advice to buy tight, and it is correct here specifically because you know the body is going to shrink back around it.

Step 5

Re-Measure Every Six to Eight Weeks

Size does not hold still. Re-measuring periodically catches change before you conclude a bra has stopped working, and it prevents the common mistake of buying several bras that only fit one phase. The bra size calculator takes about two minutes.

What to Buy, and How Many

Phase	What to buy	How many
First trimester	Soft wire-free maternity bra, wide band, no moulded cups	1 to 2
Second trimester	Maternity bra with four hook rows, stretch cups	2
From 36 weeks	Nursing bras, one cup up, band on loosest hook	2 to 3
Overnight, any phase	Soft sleep bra, no back hardware to lie on	1 to 2
Established feeding	Re-measure, then replace as needed	2 to 3 in rotation
After weaning	Wait two months for stability, then get re-measured	Rebuild from scratch

Avoid moulded cups throughout

This is the one construction to rule out at every phase. A moulded cup is heat-pressed into a fixed three-dimensional shape and holds it regardless of what is inside. Volume during pregnancy and feeding changes across a single day, not just across weeks, so a fixed shape will gape at one point and cut at another. Stretch fabric and seamed panels accommodate a genuine range, which is exactly what you need.

Questions for a Midwife Rather Than a Fitting Guide

Everything above is about garments. Some things are not, and the distinction is worth being clear about.

Contact a midwife, health visitor or doctor promptly for

A firm, painful area that does not soften after feeding. Redness or a warm patch on the breast. Flu-like symptoms alongside breast pain. A lump that persists rather than coming and going with feeds. Any nipple change or discharge unrelated to feeding. Severe or worsening pain. None of these is a bra problem, and none should be worked around with a change of garment.

It is also worth stating plainly that a bra does not affect milk supply in either direction, provided it is not tight enough to compress the breast. That is a reason to avoid anything constricting rather than a reason to go without one. And whether to wear a bra at all during pregnancy is entirely a comfort decision, with no requirement either way.

People buy six bras at four months and none of them fit by nine. Two at a time, and re-measure. The body is moving faster than a wardrobe can keep up with.
HauteFlair Fit Team

What This Means for You

A maternity bra accommodates change; a nursing bra does that and opens. Past 36 weeks, buy nursing bras, because they cover both periods and buying maternity-only means buying twice.

Expect four phases rather than one gradual increase. The band goes first, because the ribcage expands. The cup follows. Engorgement in the first week is the biggest jump and the briefest, which is why you buy one cup larger rather than sizing to it. And after weaning, things settle somewhere new rather than back.

So measure at 36 weeks, add a cup, buy the band on the loosest hook with four rows to work with, avoid moulded cups entirely, and buy two or three at a time rather than a set. Then re-measure every couple of months instead of waiting for something to stop fitting.

Ready to shop?

Maternity and Nursing at HauteFlair

Maternity and nursing bras with wide bands, four-row closures, seamed cups and drop-cup access, plus soft sleep bras. Bands 28 to 46, cups A to K. Free returns on unworn bras.

Shop Maternity & Nursing Nursing Bras for Large Busts

Frequently Asked Questions

What is the difference between a maternity bra and a nursing bra?

A maternity or pregnancy bra is built to accommodate a changing body: a wide soft band, several rows of hooks, stretch cups, wide straps and usually no rigid wire. A nursing bra has all of that plus cup access for feeding, normally a drop-cup released by a clip at the strap. So every nursing bra works as a maternity bra, but a maternity bra without cup access cannot be used for feeding. Many people buy nursing bras from the third trimester so one purchase covers both.

When should I buy a maternity bra?

Most people need one during the first trimester, since breast tenderness and early band expansion often arrive before any visible bump. Buy one or two at that point rather than a full set, because size continues to change. A soft wire-free bra with several rows of hooks will carry you a long way.

When should I buy nursing bras during pregnancy?

Around 36 weeks is the usual advice, because by then the ribcage has done most of its expanding and a measurement taken at that point is a reasonable basis. Buy two or three, one cup size larger than you measure, to allow for engorgement in the first week after birth.

How do I determine my nursing bra size while pregnant?

Measure at around 36 weeks. Take the ribcage directly under the bust, snug and level, rounded to the nearest even number, then the bust at its fullest point, and subtract the first from the second for the cup. Then buy one cup size larger than that to allow for engorgement, with a band that fits comfortably on the loosest hook.

How many nursing bras do I need?

Two or three in rotation, plus one or two soft sleep bras. Two is the practical minimum because nursing bras need washing far more often than ordinary bras and one has to be available while another dries. Buying more than three before size settles usually leaves you with bras that no longer fit.

Should I wear a bra during pregnancy?

Entirely a comfort decision. Many people find a supportive bra eases the tenderness that is common in the first trimester, and many find any band uncomfortable at times and prefer to go without. There is no requirement either way. If you do wear one, prioritise a wide soft band and no rigid wire, since both size and sensitivity change.

How much does bra size change during pregnancy?

It varies considerably between people, and the pattern is more consistent than the amount. The band usually increases first, as the ribcage expands to accommodate the growing uterus and increased lung capacity. The cup follows later, and increases again sharply when milk comes in. Many people move up one to two band sizes and one to three cup sizes overall.

Why does my band size increase during pregnancy?

Because the ribcage itself expands. The lower ribs flare outward to make room as the uterus grows and lung capacity increases, and the band measurement grows with it. This is why band size often changes before cup size does, and why people are surprised when a bra feels tight around the body before it feels tight in the cup.

Can I wear an underwire bra during pregnancy?

A correctly fitted underwire is generally fine. The practical difficulty is that size changes frequently, and a wire that fitted last month may now sit on breast tissue rather than beside it. That is why wire-free and flexible-wire constructions are the more sensible default through pregnancy and nursing, not because wires are inherently harmful.

When does engorgement happen and how long does it last?

Engorgement most commonly occurs in the first week after birth when milk comes in, and typically settles within days as feeding establishes. It produces the largest and briefest size increase of the whole period, which is why bras bought before birth should allow a cup size for it rather than being bought to fit it exactly.

Will my bra size go back to what it was before?

Often not exactly. After weaning, size usually settles somewhere new rather than returning precisely to a pre-pregnancy measurement, and both band and cup may differ. That is normal. It is worth being re-measured once things have been stable for a couple of months rather than assuming an old size still applies.

What kind of bra is best during pregnancy?

A wide soft band with four rows of hooks, stretch or seamed cups rather than moulded, wide adjustable straps and either no wire or a flexible one. Those features accommodate change rather than fighting it. Moulded cups are the main thing to avoid, since they hold one fixed shape while your volume varies within a single day.

Do I need a sleep bra during pregnancy?

Only if you want one. Some people find a soft sleep bra eases tenderness overnight, particularly in the first trimester and after milk comes in, and others find any band uncomfortable to lie in. If you do use one, choose a soft wireless style with no hooks or sliders on the back panel to lie on.

How do I use a nursing bra?

Most use a drop-cup: a clip at the top of the strap releases, and the outer cup folds down while the band and cup frame stay in place. Practise operating the clip one-handed before you need to, since you will be doing it while holding a baby and often in the dark. See the nursing bra guide.

When should I speak to a midwife about breast changes?

Contact a midwife, health visitor or doctor promptly for a firm painful area that does not soften after feeding, redness or a warm patch, flu-like symptoms alongside breast pain, a persistent lump, or any nipple change or discharge unrelated to feeding. These are clinical questions rather than fitting questions.

This article is for informational purposes only and is not medical advice, and nothing here is guidance on feeding or milk supply. Timings and size ranges quoted are general patterns and vary considerably between individuals. Any pain, lump, redness, fever or nipple change during pregnancy or breastfeeding should be assessed by a midwife, health visitor, lactation consultant or doctor.