Maternity Bra Size and Fit by Trimester

Reviewed by The Mom Store editorial team, October 2026. See our editorial policy.

A maternity bra is a soft, stretchy, usually non wired bra made to support your breasts as they grow in pregnancy. The time to switch is when your regular bras feel tight, often late in the first trimester or early in the second, and nursing bras take over in the third.

The band changes as your ribcage widens, and the cup changes on a schedule of its own. Outgrowing something you bought six weeks ago is annoying, and it is also normal. Once the baby is here, the question becomes feeding access, which is covered in our nursing bra buying guide.

What Is a Maternity Bra, and Do You Need One?

A maternity bra has stretchier cups, wider straps, a broader band and softer seams than a regular bra, so it adapts as your size changes. You do not need one on the day of a positive test. If your usual bra still fits without digging in, keep wearing it.

A bra extender, the small strip of extra hooks sold at most lingerie counters, can buy you a few more weeks in a bra you already own.

It is time to switch when:

The band rides up or leaves a red line
You spill over the top or sides of the cup
The wire sits on breast tissue instead of flat against your ribs
You are on the last hook and it is still tight

Which Maternity Bra Do You Need in Each Trimester?

In the first trimester, choose softness, because tenderness is usually the first thing you notice. In the second, choose support with room to adjust, as both band and cup grow. In the third, buy nursing bras that will carry you through the birth and into feeding.

Stage	What usually changes	What to look for	From our range
First trimester (weeks 1 to 12)	Tenderness, sensitivity, early fullness	Soft cotton, no wires, flat seams, stretch	Maternity Nursing Sleep Bra
Second trimester (weeks 13 to 27)	Ribcage widens, cups fill out, breasts feel heavier	Full coverage cups, wide straps, a stretchy band	Nursing and Feeding Non Padded Bra
Third trimester (weeks 28 to 40)	Fullest and heaviest, some leaking is possible	Nursing access, room in the cup, space for breast pads	Non padded nursing bras
First weeks after birth	Milk comes in, size shifts through the day	Stretchy cups, one hand opening, nothing tight	Crossover sleep bras

First trimester: you probably do not need to buy yet

A soft bra you already own, or a sports bra that is not tight, usually covers these weeks. If you want one new thing, make it a sleep bra. You can use it again for night feeds.

Second trimester: the one real shopping trip

This is when the band tends to get tight as the ribcage widens, and a bra that digs in all day makes anyone irritable. Look for full coverage cups, wide straps that spread the weight, and fabric with real stretch.

Our Nursing and Feeding Non Padded Bra has all three, in 92% cotton and 8% elastane, sizes S (32) to 3XL (42). The cups unclip, so it stays useful after the birth.

From our range

Nursing and Feeding Non Padded Bra, Beige

Non wired, full coverage stretch cups, with nursing clips for later. View product

Third trimester: buy for feeding

From about week 28, shop with breastfeeding in mind. NCT, a UK charity for parents, says in its guide to maternity and nursing bras that a bra bought from around 28 weeks should still fit after the birth, and that it may be best to avoid wires in the early months of breastfeeding. If your breasts feel sore, the NHS week 34 pregnancy guide suggests a light bra at night and a more supportive one during the day. Two day bras and a sleep bra or two will cover the hospital stay and the first fortnight.

From our range

Combo of 3 Maternity Nursing Sleep Bras

Three cotton crossover bras with no hooks, for late pregnancy and night feeds. View product

How Do You Find Your Maternity Bra Size?

Measure your band under the bust and your bust at its fullest point, then match both numbers to the size chart on the product page. Measure again after about two months, or on the day a bra starts to dig in, because pregnancy sizes do not stay put for long.

Wear a thin, unpadded bra and stand straight.
Band: wrap a soft tape around your ribcage right under the bust, level all the way round. Note the inches.
Bust: wrap the tape around the fullest part, loose enough to breathe easily. Note the inches.
Match both numbers to the size chart on the product page. Our clip down bras are labelled by band, S for 32 through 3XL for 42.
Try the bra on in the evening, when you tend to be at your fullest.

Three things tell you it fits:

The band sits level and two fingers slide under it
The cup covers the whole breast with no gaping and no spilling
You can take a deep breath, and the straps stay put without digging

If your bra has rows of hooks, fasten a mid pregnancy bra on the tightest row so you can let it out as your ribcage widens. Fasten a nursing bra bought in the last weeks on the loosest row so you can tighten it after the birth.

Is Underwire Safe During Pregnancy?

There is no single rule for pregnancy. As your ribcage widens, a wire that used to sit flat can start to rest on breast tissue, and that is when it gets uncomfortable. NCT advises that it may be best to avoid wires in the early months of breastfeeding. If you prefer a wired bra in pregnancy, get the fit checked, and ask your doctor about any pain or lumps.

We sell non wired bras in S to 3XL. For a wired bra, or one sized by cup, a 36D rather than an L, you will need to look elsewhere for now.

Is a Maternity Bra and Panty Set Worth Buying?

It is when you are replacing everything at once, which tends to happen around the middle of pregnancy, because both pieces arrive in the same size in one order. If your underwear still fits, skip the set.

How Many Maternity Bras Should You Buy?

Two or three at a time. Your size is likely to change again, so filling a drawer in one go usually means some of it never gets worn. A workable plan is two day bras in the second trimester, then two nursing bras and a sleep bra in the third.

How Do You Care for Maternity Bras?

Start with the care label on the bra, because fabrics differ. As a general habit, fasten the hooks before washing, use a gentle cycle or wash by hand, and let the bra air dry away from high heat. Hard wringing and hot drying wear out elastic, and the elastic is what keeps the fit.

What Mistakes Should You Avoid When Buying Maternity Bras?

Buying too many too early. Your size can keep changing, so start with two or three.
Going a size up without measuring. A bigger bra is not a better fit. Use the tape and the size chart.
Ignoring the band. It should feel secure without digging in.
Choosing looks over comfort. A pretty bra that pinches stays in the drawer.
Forgetting life after the birth. A bra with nursing clips keeps working once feeding starts.