How to Choose Maternity Activewear for Every Trimester
By AIM'N Sportswear NZ - By women | Published: 2026-10-17
Category: Buying Guides
A trimester-by-trimester guide to maternity workout clothes: what to size up, when to switch to maternity fits, and how to build pregnancy gym wear that lasts.
Quick answer
Buy maternity workout clothes one size up from your pre-pregnancy size in stretch jersey styles, and switch to dedicated maternity tops once your regular training tops start riding up. For bottoms, stay with your normal size unless the fit notes say the style runs small. Prioritise moisture-wicking, quick-drying fabric over compression, because you will re-wear these pieces through all three trimesters and into postpartum.
Trimester 1: buy for stretch, not for bump
In the first trimester your shape has not changed much yet, so this is the cheapest window to buy. Choose regular-fit training tops in soft stretch jersey rather than maternity-specific cuts, because they will still fit you at 20 weeks and again after birth. Check the fabric content before you buy: a polyester and elastane blend gives you the stretch and quick-drying performance you want, while cotton-heavy tops stay damp after a session.
If you are still running or doing higher-impact training, a supportive maternity sports bra matters more than a new top. Look for one that adjusts at the band, since ribcage measurements change faster than cup size in early pregnancy.
Trimester 2: the switch point for tops
The moment your regular tops start riding up mid-workout, move to maternity cuts. Maternity tops are cut longer through the body and shaped over the bump, so they stay put during squats, rows and mat work. This is also when you should stop sizing down in the hope of a tighter fit; a top that pulls across the bust restricts breathing and will not last to the third trimester.
Shorts and leggings usually still work in your pre-pregnancy size at this stage if the waistband sits below the bump. If a waistband digs in, that is your signal to change style rather than size.
Trimester 3: comfort and coverage over compression
By the third trimester, breathability and easy on-and-off matter more than sculpting. High-waisted styles that sit over the bump distribute pressure better than low-rise bands, and laser-cut edges reduce bulk under clothing. Keep your session intensity in mind: for walking, yoga and strength work you do not need heavy compression, just fabric that wicks and dries.
Buy fewer pieces at this stage. A long sleeve, a short sleeve and one pair of shorts will cover most weeks, and they will still fit postpartum while your body settles.
Fabric and care checks before you pay
Read the material list on every product page. A blend around 88% polyester and 12% elastane gives you the soft handfeel and recovery you want for a garment that will be washed twice as often as your pre-pregnancy kit. Avoid anything described only as 'cotton-rich' for sweaty sessions, and skip delicate trims that will not survive frequent washing.
Wash in cold water and air dry where you can. Heat is what kills elastane recovery, and losing stretch is the main reason maternity activewear stops fitting before the pregnancy ends.
Decision rules for each trimester
- If your regular tops still cover your bump: Stay in your normal size and buy regular-fit stretch jersey rather than maternity cuts. You get more wear out of the piece and can keep using it postpartum. Switch to maternity cuts only when tops start riding up mid-session.
- If a fit note says the style runs small: Size up one, as advised for the Sense Biker Shorts. Maternity sizing is not vanity sizing; a band that digs in is a fit problem, not a motivation problem. Trust the brand's fit note over your usual size.
- If you are buying for the third trimester only: Choose high-waisted bottoms and one long sleeve and one short sleeve in the same size. Skip compression-led styles unless your training specifically calls for them. Fewer, softer pieces beat a full new wardrobe at 35 weeks.
- If you are unsure between two sizes: Take the larger size in tops and follow the fit note on bottoms. Fabric with elastane will relax slightly with wear, but it will not stretch to cover a bump it was not cut for. Buy for the size you will be in a month, not today.
AIM'N pieces that work across trimesters
- Black Soft Basic Maternity Long Sleeve: Soft Basic Maternity Long Sleeve in black, made from a super-soft, quick-drying stretch jersey in 88% polyester and 12% elastane, with a rounded neckline, shaping details and a regular fit. The long sleeve is the piece to buy if you train outdoors or in a cold gym, and the regular fit means it works from the second trimester into postpartum without sizing up again.
- Black Soft Basic Maternity Short Sleeve: Soft Basic Maternity Short Sleeve in black, same Soft Basic maternity fabric, moisture-wicking and quick-drying, with a rounded neckline and regular fit. A short sleeve is the better choice for indoor sessions and warmer months; because it shares the same fabric and fit as the long sleeve, you can buy both in one size and know they will behave the same way.
- Dark Clay Sense Biker Shorts: Sense Biker Shorts in Dark Clay, made from brushed Sense fabric with a second-skin feel, a high waist, laser-cut edges, and a tight fit that runs small, so the brand advises choosing one size larger. This is the one piece where you should deliberately size up rather than trust your usual size, and the high waist sits over the bump instead of cutting under it.
Who this approach suits
Best for
- Mums-to-be who want maternity workout clothes that last from the second trimester into postpartum
- Walkers, yoga and strength-training sessions where breathability matters more than compression
- Anyone building pregnancy gym wear around two tops and one pair of shorts
Not for
- Runners who need high-compression support and should look at a dedicated maternity sports bra first
- Anyone shopping for high-impact sport-specific kit, where fit and support requirements differ
