How to Choose the Right Size in Maternity Underwear

Quick answer

To choose the right size in maternity underwear, measure your hips and belly at their current size, then pick a style that matches your fit preference: under-bump for low-rise comfort, over-bump for full coverage, or seamless for no lines. When in doubt, size up—stretchy fabrics accommodate growth, but too-tight elastic can irritate a postpartum belly.

Shopping for maternity underwear feels different from buying regular panties because your body changes week to week. The right size isn't about your pre-pregnancy number—it's about how the fabric and waistband sit on your bump and postpartum belly. This guide breaks down sizing rules for the most common maternity underwear styles so you can buy with confidence once and avoid a drawer full of misfits.

We'll cover how to measure, how each style fits at different stages, and when to choose a specific cut. You'll also see how real product features—like stretchy fabric and no-roll waistbands—translate into everyday comfort.

How Maternity Underwear Sizing Works

Most maternity underwear uses the same size chart as your regular underwear, but the fit depends on where the waistband sits. Under-bump styles (like bikinis) sit below your belly, so your hip measurement matters most. Over-bump styles (like briefs) stretch over your bump, so you need enough fabric and stretch to cover your growing belly without digging in.

Because maternity fabrics are designed to stretch, you often don't need to size up until late pregnancy or if you gain significant weight. The key is to check the fabric content and the waistband design. Look for words like 'stretchy,' 'no-roll,' or 'adaptive'—these features do more for comfort than a larger size number.

• Measure your hips at the widest point and your belly at its current size, then compare to the brand's size chart.
• If you're between sizes, size up for over-bump styles and down for under-bump styles if you prefer a snug fit.
• Remember that postpartum bodies change quickly; buying a multi-pack in your current size is safer than stocking up too early.

Under-Bump vs. Over-Bump: Which Fit Is Right?

Under-bump underwear sits below your belly, making it a favorite for moms who don't want anything pressing on their bump. It's also easier to wear with low-rise pants or during early postpartum when your belly is still shrinking. The trade-off is less coverage and a potential for the waistband to roll if it's not designed well.

Over-bump briefs provide full coverage and support, which can feel reassuring in late pregnancy. However, they can feel warm or restrictive in summer, and some moms find them uncomfortable after a C-section because the waistband sits near the incision. Your choice should reflect your stage and personal sensitivity.

• Try a mix: under-bump for daytime and over-bump for lounging or sleeping.
• If you have a C-section scar, choose underwear with a soft, stretchy waistband that sits below the incision.

Fabric and Features That Affect Fit

The fabric determines how forgiving the underwear is. Bamboo and modal blends are breathable and soft, while cotton gussets add hygiene. Seamless designs reduce irritation and are invisible under leggings. A no-roll waistband is crucial for under-bump styles, as it prevents the dreaded roll-down that causes discomfort.

Pay attention to the rise: high-rise briefs offer more belly coverage, while low-rise styles are cooler. If you're between sizes, a stretchy fabric can make the smaller size work, but never choose a size that leaves red marks or digs in—that's a sign it's too tight.

• Look for a cotton gusset for breathability and to reduce infection risk.
• Seamless styles are ideal for wearing under fitted dresses or yoga pants.

Decision Rules for Buying Maternity Underwear

• Stage of pregnancy: First trimester: your pre-pregnancy size likely fits. Second trimester: switch to maternity styles when your regular underwear feels tight. Third trimester: choose over-bump briefs for support or under-bump for comfort. Re-evaluate your size each trimester.
• Postpartum recovery: After birth, your belly shrinks gradually. High-rise briefs can provide gentle support, but avoid anything with a tight waistband if you had a C-section. Under-bump styles are often more comfortable initially. Buy a few pairs in a size that fits your immediate postpartum belly.
• Style preference: Under-bump bikinis are best for low-rise comfort and wearing under pants. Over-bump briefs offer full coverage and support. Thongs eliminate lines but may not be suitable if you have hemorrhoids or need extra coverage. Match the style to your daily outfits and comfort needs.

Real Maternity Underwear Options to Consider

• Under-the-Bump Bikini Underwear Pack | Low Rise Style - Neutrals: Features stretchy fabric that sits just below your baby bump and naturally conforms to your changing body, with a clever notched design and no-roll waistband. This style is ideal if you prefer low-rise coverage that doesn't press on your belly. The no-roll waistband means it stays put all day, and the five-pack gives you options as your size fluctuates.
• Bamboo Maternity & Postpartum Thong | Beige: Seamless maternity thong with a non-rolling, crossover waistband that sits below the bump, made from soft bamboo with a 100% cotton gusset. If you hate panty lines, this thong offers a seamless option with breathable bamboo fabric. The crossover waistband adapts to your changing shape without digging, and the cotton gusset is gentle for sensitive postpartum skin.

Fit Guidance at a Glance

Best for

• Under-the-Bump Bikini Underwear Pack: Best for moms who want low-rise comfort without pressure on the bump, especially in the second and third trimesters.
• Bamboo Maternity & Postpartum Thong: Best for moms who prioritize no panty lines and prefer breathable, seamless fabric.

Not for

• Under-the-Bump Bikini Underwear Pack: Not ideal if you prefer full belly coverage or need support over your bump.
• Bamboo Maternity & Postpartum Thong: Not suitable if you dislike thongs or need extra coverage for postpartum discharge or hemorrhoids.

Finding the right maternity underwear size comes down to measuring your current body, choosing a style that matches your comfort needs, and being willing to adjust as you progress through pregnancy and postpartum. Start with a versatile pack that covers your early needs, and don't hesitate to try a different cut when your body changes.