Maternity Bra Size by Trimester

First trimester (weeks 1 to 12)

• What often happens: tenderness and a feeling of fullness, sometimes within the first few weeks. Some people gain a cup size early. The ribcage has not changed much yet.
• What to do: if your bras are comfortable, keep wearing them. If they feel tight or the wires press, move to a soft, non-wired bra or a crop-top style. There is no need to buy maternity bras in advance.

Second trimester (weeks 13 to 27)

• What often happens: steady growth in the cup. The ribcage starts to widen as the baby grows, so bands begin to feel tight.
• What to do: this is when most people need new bras. Measure, and buy one or two maternity or nursing bras that fit on the tightest hook, leaving room to let the band out. A bra extender is a cheap way to get more wear from bras whose cups still fit.

Third trimester (weeks 28 to birth)

• What often happens: the ribcage is at its widest. Breasts may feel heavier, and some people leak a little colostrum.
• What to do: check your size again around 28 to 30 weeks. From about 36 weeks, buy your first nursing bras, fitted on the loosest hook with room in the cup. See when to buy nursing bras.

After the birth

• What often happens: milk comes in a few days after birth, and breasts can be much fuller for a time. The ribcage gradually narrows over the following weeks. Size settles at around six to eight weeks if you are feeding.
• What to do: wear soft, flexible nursing bras at first, and re-measure once things settle.

Which hook, when

Measuring while pregnant

1. Measure under the bust, snug but comfortable. Do not pull the tape tight.
2. Measure around the fullest part of the bust, wearing a soft, unpadded bra if going without is uncomfortable.
3. Enter both in the nursing bra calculator with your stage.
4. Repeat every six to eight weeks, or whenever a bra stops being comfortable.

Signs your bra no longer fits

• The band feels tight on the loosest hook
• Wires press into breast tissue at the side or centre
• You are bulging over the top or sides of the cups
• You have red marks that last, or you are relieved to take it off

What to look for in a maternity bra

• Soft, breathable fabric with some stretch in the cup
• Four or more rows of hooks, or room for an extender
• Wide straps and a deep band
• Non-wired, or with flexible wires
• Drop-cup clips, if you want it to serve as a nursing bra later

For night-time comfort, see sleep bras for pregnancy and nursing.

Frequently asked questions

Do you need a bigger bra when pregnant?

Most people do at some point, though how much and when varies a great deal. Both the cup and the band commonly increase. Change when your current bras become uncomfortable, not at a set week.

How many cup sizes do you go up in pregnancy?

It varies from very little to several cup sizes. One to two is often quoted as typical, with a further increase when milk comes in. Measure, and do not rely on averages.

How do I measure my bra size while pregnant?

In the usual way: snugly under the bust for the band, and around the fullest part for the cup. Go by comfort on the band, since your ribcage is expanding, and re-measure every six to eight weeks.

Can I wear underwired bras while pregnant?

Many people do if they are comfortable and the wire sits on the ribcage, not on breast tissue. As size changes quickly, a wire that fitted last month may press this month, which is why non-wired styles are popular. Ask your midwife if you are unsure.