This is sizing guidance, not medical advice. Breast changes in pregnancy and feeding vary a great deal from person to person. If you have pain, a lump, redness or anything that worries you, contact your midwife, health visitor or GP.
How your size changes, stage by stage
During pregnancy
Breasts often begin to change in the first trimester, and the ribcage expands as the baby grows, particularly in the last few months. Both the band and the cup tend to go up, and at different rates for different people.
There is no need for a special bra the moment you are pregnant. Change when your usual bras stop being comfortable. When you do, choose one that fits on the tightest hook, so there is room to let it out as your ribcage expands. Re-check your size every six to eight weeks.
Late pregnancy: buying nursing bras
From about 36 weeks your measurements are a reasonable guide to the first weeks after birth. Two adjustments apply:
- Allow extra room in the cup, typically one cup size, for when your milk comes in.
- Fit the band on the loosest hook. Your ribcage normally draws in again after birth, and the remaining hooks let you tighten the band as it does.
Buy one or two at this stage. A larger set is better left until you know what size you settle at.
The first six weeks
This is when size is least predictable. Breasts can be much fuller for a few days when milk first comes in, and they change from feed to feed. Soft, stretchy, non-wired styles and sleep bras are the most forgiving. A precisely fitted bra bought now may not fit in a month.
Established feeding
After six to eight weeks supply usually settles and your breasts change less through the day. This is the time to measure properly and buy the nursing bras you will wear for the months ahead. Measure when you are comfortably full, and look for a cup with a little stretch at the top edge.
After you stop breastfeeding
Breasts commonly change again in size and shape. Give it a few months to settle, then measure from scratch. It is normal to end up in a different size from the one you wore before pregnancy.
Each stage is covered in more depth in maternity bra size by trimester, when to buy nursing bras and bra size after breastfeeding.
What to look for in a nursing bra
- Clips you can undo with one hand. You will be holding a baby with the other.
- A full sling or A-frame behind the drop cup. This keeps the breast supported while the cup is open.
- Four or more rows of hooks. More adjustment covers more of the changes in your ribcage.
- Soft, breathable fabric. Skin is often more sensitive, and breast pads need room.
- No pressure points. Nothing should press into breast tissue at the sides or underneath. The usual fit checks still apply.
Types of nursing bra, and which suits each stage and cup size, are compared in best nursing bras: what to look for. For nights, see sleep bras for pregnancy and nursing.
Getting fitted in person
Maternity fittings are widely available. John Lewis offers a dedicated maternity fitting appointment, and many independent lingerie shops and specialist fitters do the same. A fitter can judge shape and room in a way a tape measure cannot, which is especially useful at a time when your size is moving. Our guide to the best places for a bra fitting in the UK covers the options.
Frequently asked questions
When should I buy nursing bras?
Most fitters suggest late pregnancy, from around 36 weeks, for the first one or two. Your ribcage and breasts are then close to the size they will be in the first weeks after birth. Buy only what you need to start with, because your size will settle again once feeding is established.
How much room should I allow in a nursing bra?
A common rule of thumb is about one cup size of room in late pregnancy, to allow for your milk coming in. Some people need more. Cups with stretch in the upper section cope with the changes through the day better than rigid ones.
Which hook should a nursing bra fasten on?
Bought in late pregnancy, it should fit on the loosest hook. Your ribcage usually narrows in the weeks after birth, and the tighter hooks let the band follow it. A maternity bra bought early in pregnancy is the opposite: fit it on the tightest hook so you can let it out as you grow.
Can I wear an underwired bra while breastfeeding?
Many people do, but fit matters more than usual. Any bra that presses on breast tissue can be uncomfortable when your breasts are full, and breast size changes through the day while feeding. This is why non-wired and flexible-wire styles are popular, especially in the early weeks. If you have pain, redness or a lump that does not clear, speak to your midwife, health visitor or GP.
When should I re-measure after having a baby?
Once feeding has settled, usually around six to eight weeks after birth, and again a few months after you stop breastfeeding. Your size at each of these points can be different.
Finished feeding? Your size has probably changed again.
Re-measure with the main calculator →