You're heavily pregnant and you want everything ready. The hospital bag is packed, the crib is up, and there's one thing left on your list: a nursing bra. So you measure yourself, or get measured, and you order a lovely set in your size. Done. One less thing to worry about.
And then, in week one, your milk comes in. Within a day your breasts turn hard, full and noticeably bigger than they were at 36 weeks. That perfectly fitting bra you so sensibly bought in advance suddenly digs in. And you think: did I order the wrong size?
No. You measured at the wrong moment. On every forum where expectant mums ask about this, the same experienced voice comes back: hold off for now, you don't yet know what your breasts are going to do. It sounds like putting things off, but it's the best advice you'll get. Below you'll read why, and what to buy in advance instead.
Short answer, in two parts. One: before the birth, don't buy your final fitted set. Buy one or two soft, wire-free bras with stretch that move with your breasts while your size shifts. Two: hold the real shopping until after your milk comes in, once the biggest surge has settled and your size has steadied a few weeks later. That's when you measure what you'll actually wear.
Why your 36-week bra digs in by week one
Here's the mistake nearly every expectant mum makes. And it's a reasonable one. You think of your breast size as one number you measure once. In reality, over a few weeks you don't have one breast but three different ones.
Breast one is the late-pregnancy breast. During pregnancy your breast tissue grows under the hormones and your ribcage widens. You've probably already gone up a cup size or two compared with before you were pregnant. This is the breast you measure at 36 weeks.
Breast two is the engorged breast, and this is the biggest. Around day three to five after the birth your milk comes in. Your breasts fill up, turn taut, warm and hard, and within a day they can get considerably bigger than they've ever been. Mums describe breasts that went genuinely huge with the engorgement. This peak is temporary. It's also exactly the moment when a fitted 36-week bra can't possibly fit any more. Some women find their size changes hour to hour in this phase: full just before a feed, emptier straight after.
Breast three is the settled nursing breast. After the first few weeks your milk supply settles to your baby. The biggest swelling goes down, and for a lot of women the size drops back a little. A cup that got added during engorgement often partly comes back off within weeks. This is the size you'll wear for months. It's usually not the peak size, and not your 36-week size either.
That's exactly why the bra you bought in advance digs in. Not because you measured wrong, but because you locked in one size for a breast that has three of them in a short space of time. And how much your breasts swing isn't something you can predict. One woman goes from a DD to a G cup in the first months, another adds a single cup and it drops back quickly, someone else barely changes. Your old size and your 36-week size aren't a reliable starting point for what happens after the birth.
When measuring actually makes sense
The root of the confusion is the assumption that you can measure during pregnancy for the time after it. That doesn't work, and the mums who've been through it are very firm about it: what you measure before the birth tells you little about what happens after. For one, the breasts get enormous; another loses a bit around the bust. So measuring isn't pointless, it just only makes sense at the right moments.
Measure moment one around week 38, for a bridge bra. By late pregnancy your breasts have already changed from your old size. Measure then, so you can buy a soft bra that's comfortable now and has enough stretch to take in the first swelling after the birth. This is a bridge, not a final size.
Measure moment two a few weeks after the birth, once your size steadies. Wait until the milk-coming-in peak has settled and you're holding roughly the same size several days in a row, rather than a different one every feed. That's when you measure what you'll actually wear, and that's when you buy your final set. The exact technique for band and cup, and how to feel with two fingers whether it fits without digging in, is in how to measure a nursing bra and find the right fit.
Measuring during the engorgement peak itself is pointless. You'd be measuring the biggest, most temporary spike, and a bra in that size will be too loose within weeks.
How many nursing bras should you buy in advance?
The pattern in the mum threads is strikingly consistent. And it runs straight against the urge to have everything ready in advance. Almost nobody recommends a full fitted set before the birth. The advice that keeps coming back: buy two in advance, see how it goes, and stock up on the rest only after the birth, once the biggest size change is behind you.
There's a reassuring logic to it, and it's kinder to your wallet too. A lot of women worry they'll have to buy twice: first in the wrong size, then a whole expensive set again straight after the birth. That's exactly the worry you avoid by keeping it small in advance. One or two good, stretchy bras bridge the whole period when your size is still moving every which way. You buy the rest deliberately later, once you know what you're wearing.
Plan for change rather than one perfect size. Keep enough of your bridge bras to rotate while one's in the wash. Only top up once you notice your size is stable. That way you never buy a drawer full of bras that stop fitting after two weeks.
Old size or a size up? The gamble you don't have to take
This is where most mums get stuck. Do you go for your current size in advance, or take a punt on a size up for the swelling that's coming? The honest answer: both are a gamble, and you don't have to do either if you choose stretch in advance instead of a fixed number.
Still, it helps to know what actually shifts, because it's more than you'd think. It isn't only the cup. Your band size isn't fixed either. During pregnancy your ribcage widened, but after the birth it can narrow again once the baby is no longer pushing your ribs up. For some women the band size changes the other way. A woman might have a narrow band with a large cup before the birth and end up on both a different band and a bigger cup while nursing. So if you blindly buy a cup size up in advance, your band still won't necessarily be right.
If you do want something fitted in advance, use the rule of thumb experienced mums pass on: there should be room in the cup. A handy check is that your flat hand fits comfortably alongside your breast in the cup, so there's space for the milk coming in and for a breast pad. If the cup is already snug around your breast alone, it'll be too small within days.
But the better approach is that you don't have to take that gamble at all. A soft, wire-free bra with stretch in the band and the cup moves with the swing, from your late-pregnancy breast, through the engorgement peak, to your settled size. It's exactly why so many mums prefer a soft, wire-free nursing bra for the end of pregnancy and the first stretch after: it takes in the changing size without you having to guess in two directions, and without spending again straight after the birth. Stretch instead of a fixed number isn't one of the options, it's the answer to this whole phase. And if you're also wondering whether you're leaking now or will leak later, and which bra keeps you dry, compare the absorbent options in which nursing bra is genuinely leak-proof?.
When a bra that digs in is a reason to get in touch
A bra that digs in, you take off and swap. Usually that's the whole story, especially in those first days when your breasts are full and taut. But a few things aren't part of a normal size change and are worth getting looked at. Contact your GP or midwife, or during the day a lactation consultant or your health visitor, if you have:
- A fever or a flu-like, run-down feeling alongside a breast symptom.
- A red, warm, painful patch or a hard area in your breast, especially if you feel yourself getting unwell quickly. This can be a sign of mastitis (an inflamed, and sometimes infected, breast) and needs checking.
- A hard spot or lump that doesn't clear after a feed or after a couple of days.
- Bloody or unusual discharge from the nipple that comes from one breast only, keeps going, or smells or looks odd, aside from cracked nipples. If you notice discharge like this during pregnancy too, that's one for your GP or midwife.
In the UK you can get breastfeeding support from your health visitor, an NHS breastfeeding helpline, or a local infant feeding team. But with a fever or a red, painful breast, your GP is the first port of call, not the helpline, or NHS 111 out of hours. In that full first week, watch too that your bridge bra doesn't cut in anywhere: constant pressure on full breast tissue can contribute to a blocked milk duct. The right nursing bra keeps you comfortable and dry. It isn't a fix for a medical problem, and it should never hide one.
A bra that moves with all three sizes
We built our nursing bra for exactly this phase, when your size is still shifting. It's wire-free and the band gives as your breasts swell, so it moves with the peak instead of cutting in. That's exactly what you're after in advance: not a fixed number that stops fitting once your milk's in, but stretch that takes in the swing.
And because the protection against leaking is already in the cup, four layers with a core that holds up to 30 ml per cup, there's no loose pad to shift out of place just when your breasts are at their fullest. The clip opens one-handed, handy for a feed and in the dark at night too. Knitted from an OEKO-TEX Class I certified fabric (certificate number 11-36224), the strictest category, for textiles that touch the skin of babies under three. Designed in Belgium, knitted in Türkiye.
If you'd like to see it, you can here: see the nursing bra. If you're still in the thick of pregnancy and already leaking a little colostrum, read what's normal at that stage in leaking colostrum during pregnancy. And if you'd like everything about nursing bras, fit and comfort in one place first, head to the guide to nursing bras, fit and comfort.
Frequently asked questions
When is the best time to buy a nursing bra, during pregnancy or after the birth?
A bit of both. Around week 38, buy one or two soft, wire-free bras with stretch as a bridge, and hold your final set until a few weeks after the birth. By then the biggest swelling from your milk coming in has settled and your size has steadied, so you measure and buy what you'll actually wear.
Can I get my nursing bra size measured during pregnancy?
Measuring during pregnancy tells you little about the time after. Around day three to five your breasts fill up and get temporarily much bigger, then it goes down again. So measure around week 38 for a bridge bra only, and measure again once your size has steadied a few weeks after the birth. That's when you get your real nursing size.
How many nursing bras do I need before the birth?
One or two is enough. Almost no experienced mum recommends a full fitted set in advance, because your size still changes too much. Two stretchy bras bridge the whole shifting period, and you keep one clean while the other's in the wash. You buy the rest deliberately after the birth, once you know what fits.
Should I buy a size up in advance for when my milk comes in?
You don't need to if you choose stretch. A blind size up is a gamble, because it isn't only your cup that changes but your band size too, sometimes in both directions. A soft, wire-free bra with stretch in the band and cup moves with the swelling, so you don't have to guess the exact size, and you don't have to buy again straight after the birth.
More articles
- Which nursing bra suits which moment: night, work, sport, pumping
- Signs of a poor fit or compression
- Breast pads: which ones do you need, and when?
- When does the leaking stop? Patterns from week 1 to winding down
- Nursing bras, fit and comfort: the guide
