How Your Size Changes
Breast and ribcage size change significantly throughout pregnancy and nursing — and not just once. Most women go through at least three distinct size phases, each requiring different bra solutions.
Early breast growth and tenderness
Breast tissue begins growing almost immediately due to hormonal changes. Many women experience significant tenderness and soreness. Existing bras can feel painfully tight even when the size hasn't changed dramatically yet. The ribcage typically hasn't expanded yet at this stage.
Ribcage expansion begins
As the uterus grows upward, the ribcage expands outward to accommodate it. Band size typically increases by 2–4 inches over this period. Cup size also continues growing. This is when most existing bras stop fitting entirely — both too tight in the band and too small in the cup.
Maximum size reached
The ribcage is at or near its maximum expansion. Breasts have grown significantly — typically 1–3 cup sizes from pre-pregnancy. Many women find they've gone from a 34C to a 38E or from a 36D to a 40G or larger. This is also when colostrum may begin to be produced, making nursing preparation relevant.
Milk comes in
When milk production begins (typically day 3–5 after birth), breasts can increase by another 1–2 cup sizes almost overnight. This is temporary — engorgement settles as supply regulates, usually within 4–8 weeks. This is the most dramatic size change and the most uncomfortable if the bra no longer fits.
Size stabilises for nursing
Milk supply regulates and breast size becomes more predictable. The ribcage begins contracting back toward pre-pregnancy size, but may not fully return if this was not your first pregnancy. This is the right time to invest in 3–4 nursing bras for the duration of breastfeeding.
When to Buy
| Stage | When to buy | How many | Type |
|---|---|---|---|
| Early pregnancy (tender) | As needed from week 6–8 | 1–2 | Soft wire-free or sleep bra |
| Maternity bras (main) | Around week 14–16 | 2–3 | Maternity underwired or wire-free |
| Third trimester update | Week 36–37 | 1–2 more if needed | Maternity or nursing bra |
| Nursing bras (first weeks) | Week 36–38 (before birth) | 2–3 | Soft nursing bra with stretch |
| Nursing bras (long-term) | 6–8 weeks postpartum | 3–4 | Full nursing bra with underwire |
| Post-weaning | When fully weaned | As needed | Regular bras in new size |
How to Measure During Pregnancy
The measurement method is the same as always — but timing and interpretation require care.
Taking measurements
Measure your underbust snugly (not tight — two fingers should fit) and your bust loosely around the fullest point. During pregnancy, wear a non-padded bra or no bra. The difference between bust and underbust is your cup size.
When to remeasure
During pregnancy: measure every 4–6 weeks or whenever current bras feel tight. After birth: measure again at 3–5 days postpartum, then again at 6–8 weeks when supply stabilises. After weaning: measure 4–6 weeks after fully stopping breastfeeding.
Maternity Bras
A maternity bra looks similar to a regular bra but is specifically engineered for a changing body — more adjustability in the band, softer materials, expandable cups, and construction that avoids pressure on growing breast tissue.
Maternity underwired
A maternity bra with underwire that is positioned slightly lower and wider than in a regular bra, avoiding pressure on breast tissue that extends further during pregnancy. Provides more lift and shape than wire-free alternatives. Safe from the second trimester onwards for most women.
Wire-free maternity
Structured maternity bra without underwire. Uses wide bands, seamed cups, and reinforced fabric for support without metal. Ideal throughout the first trimester and for women who find any underwire uncomfortable during pregnancy. Also appropriate for post-surgical situations.
What to look for
Multiple rows of hooks (at least 3–4 positions) to accommodate band expansion. Soft, non-irritating fabrics. Wider straps for comfort. Cups with some additional volume or stretch for growth. Avoid under-bust seaming that digs in as the ribcage expands.
Maternity vs nursing
Maternity bras are for wearing during pregnancy. Nursing bras have an additional drop-down cup mechanism (clip or pull-aside) that allows access to the breast for feeding. Some bras are designed as maternity-to-nursing bras that serve both purposes — a practical choice for the third trimester purchase.
Nursing Bras
A nursing bra has a drop-down or pull-aside cup that allows breastfeeding access without removing the bra. The mechanism matters — some are more convenient than others depending on where and how you nurse.
Clip-down nursing cup
The most common nursing bra mechanism. A clip at the top of each strap releases the cup, which folds down to expose the breast. Can be operated one-handed once you're practiced — important for feeding a baby while standing or in public. Most supportive nursing bra type.
Pull-aside cup
The cup fabric pulls to the side to expose the breast rather than folding down. Usually found in softer, sleep-style nursing bras. More comfortable but slightly less discreet than clip-down styles — the cup doesn't stay fully out of the way. Good for home use and night nursing.
Underwired nursing
A nursing bra with underwire. Provides the best shape and support, particularly for larger cup sizes. Once controversial — old advice warned against underwire during nursing due to blocked duct risk — but modern nursing underwires are positioned correctly and safe if the bra fits well. Never wear a nursing underwire that feels tight or digs in.
How many do you need?
Plan for 3–4 nursing bras in regular rotation — one on, one in the wash, one drying, one spare. Nursing bras get washed frequently (leaking, spit-up, sweat). Invest in 2 good underwired nursing bras for daytime and 2 soft sleep nursing bras for night. Replace when the band stretches or the clips fail.
Sleep & Night Bras
Many women choose to wear a bra at night during pregnancy and nursing — for comfort during engorgement, to hold breast pads in place, and to reduce leaking onto clothing.
Sleep nursing bra
A soft, wire-free bra with pull-aside or clip-down nursing access, made from stretch jersey or modal fabric. Should feel like wearing nothing — no hooks digging in, no underwire, full stretch. Holds a breast pad in place. The most important feature is softness: you'll spend 8 hours in it while sleeping and nursing multiple times.
Do you have to wear a bra at night?
No — it is entirely personal preference. Wearing a bra at night does not prevent sagging (that is determined by ligament integrity and genetics, not bra use). During nursing, a sleep bra helps hold breast pads in place to prevent milk from soaking clothing. Many women find comfort support during engorgement helpful.
Brands to Shop
Recommended maternity & nursing brands
All stock extended sizes — most go to at least G or H cup in nursing styles.
Frequently Asked Questions
Measure today — get your current size
Your size changes throughout pregnancy and nursing. Use our free calculator at every stage to stay in the right bra — for comfort, support, and your health.
Calculate My Size →