Do you size up in maternity clothes?
The instinct is to buy bigger — you’re growing, after all. It’s also the most expensive mistake in maternity shopping. Here’s what actually happens to your size, and the handful of times you genuinely should go up. It’s the whole reason 9Edits exists: honest, measurement-based fit advice instead of guesswork.
The short answer: no — in most maternity clothes you take your pre-pregnancy size. A well-made maternity garment is engineered to grow: the panel, the ruching and the stretch do the expanding, so the number on the label stays the same from first bump to birth.
Why “just size up” is usually wrong
The whole craft of maternity design is expansion that’s already in the garment. Stretch panels that unfold over the bump. Ruching at the side seams that releases as you grow. Empire seams that fall from above the bump rather than the waist. None of that needs a bigger size — that is the bigger size, built to arrive exactly when you need it.
Buy up on top of all that and you get the worst of both ends: swamped and shapeless early on, and — once the bump fills the panel — a saggy seat and dropped shoulders that never quite sit right. The same size is meant to carry you the whole way.
The five times you actually should size up
The pre-pregnancy rule holds most of the time — but not always. These are the honest exceptions, and knowing them in advance is the difference between one order and three.
- The brand runs small. Some labels — usually premium, tailored ranges — cut slim to begin with. If a brand runs small in its regular line, it runs small in maternity too. Our brand-by-brand jean fit guide flags who does.
- You’ve gained beyond the bump. Many people carry a little extra through the hips, back and thighs — places the panel doesn’t cover. If that’s you, size up for the leg and seat even when the bump would fit your usual number.
- It’s your bust. Your ribcage and cup size change early and a lot. Bras, and anything fitted through the chest, follow their own rules — measure rather than assume.
- The style is tailored with little stretch. Structured blazers, stiff woven dresses and non-stretch trousers have no give to spare. On those, size up one for comfort through the bump and hips.
- You’re between sizes on an under-bump cut. An under-bump band can’t stretch upward, so if you’re on the line, size up so it sits securely below the bump. On an over-bump panel, do the opposite — take the smaller size.
How maternity sizes actually map
Most UK maternity ranges use your pre-pregnancy dress size — a maternity 12 is built for someone who wore a 12 before. Some brands switch to S/M/L, which is more forgiving but vaguer; when they do, size to the body measurement on their chart, not the letter. A few bake a trimester assumption into the cut, running slightly roomy on the expectation you’ll grow in. The label alone won’t tell you which — but the measurement will. Our full sizing guide walks through reading a chart.
The one measurement that settles it
Forget the dress-size label and measure the fullest part of your hip and seat — that’s the number that decides fit in a true-to-size maternity garment, because the panel handles the bump and the hip handles everything else. Take it once, keep it on your phone, and check it against each brand’s own chart. It’s a two-minute habit that ends the returns cycle for good — our guide to measuring yourself shows how to take the number properly.
Common questions
Do maternity clothes run true to size?
Most quality maternity clothes are designed to run true to your pre-pregnancy size — the garment expands through built-in panels, ruching and stretch, so the label stays the same. Exceptions are brand-specific: budget ranges often run generous, premium tailored labels often run slim. Check the brand’s own size chart to be sure.
Should I buy my normal size in maternity clothes?
Usually yes — order the size you wore before pregnancy. The panels and stretch are engineered to accommodate the bump at that size, so going bigger just leaves excess fabric that sags once the bump fills out.
Won’t maternity clothes get too big after the bump goes down?
Under-bump and side-panel styles carry over best after birth — they look most like regular clothes and support a softer middle. Over-bump styles are lovely while pregnant but tend to slide once there’s no bump to hold the panel up, so they’re less useful afterwards regardless of size.
Do I need to size up for the third trimester?
No — a true-to-size maternity garment is designed to fit through the third trimester at your original size; that’s the whole point of the panel. If something feels tight late on, it’s usually a brand that runs small or growth beyond the bump, not a sign you needed a bigger size all along.