Maternity Underwear: What to Look for in Each Trimester

By Lace Laboratory | Published: 2026-10-13

Category: Buying Guides

A trimester-by-trimester guide to maternity underwear fit, including when to size up, how stretch lace adapts as your body changes, and what to skip.

Quick answer

Buy for the trimester you are in, not the one you plan to be in. In the first trimester, most people can keep their usual underwear and simply size up when a waistband starts digging. By the second and third trimesters, prioritize a waistband that sits below or well above the belly, fabric that stretches without losing shape, and a bralette that clips at the back so you can adjust as your ribcage expands. Stretch lace that adapts to your body, like Lace Laboratory's signature lace, handles that change better than rigid cotton because it moves with you instead of fighting you.

First trimester: the waistband is your first warning sign

Early pregnancy bloating can make your regular underwear feel tight before you look any different. The practical rule: if you have to tug at the waistband more than once a day, it is already too small. You do not need a full maternity drawer yet. Buy one size up in a style you already like and keep the rest of your rotation.

This is also the trimester where a thong works well for many people because there is no fabric riding up under a changing belly. The catch is the waistband height. A low-rise band that sat flat before may now roll or dig. Check where the band lands when you sit down, not just when you stand.

Second trimester: switch to a band that respects the bump

Once your belly starts to round, the decision is between a below-bump band and an over-bump band. Below-bump styles sit on the hip and stay out of the way, which suits people who feel pressure on the belly. Over-bump styles, including high-waist cuts, distribute pressure across a wider area and can feel more secure if you are active.

Stretch percentage matters more than size number here. Lace that stretches up to 150% and returns to shape will follow a bump that grows week to week, so you are not rebuying every month. Rigid fabrics with a fixed waistband will not do that, no matter how many sizes you try.

Third trimester: support, breathability, and a bralette that adjusts

In the final stretch, comfort is about pressure distribution and heat. Look for a waistband that is wide enough not to cut in and a fabric that breathes. A high-waist thong gives you coverage across the lower belly without a full brief silhouette, which some people prefer under dresses and leggings.

Your ribcage can expand by a band size or more, so a bralette with adjustable straps and a back clip is more forgiving than a fixed-band bra. Wire-free construction matters too: wires that fit at 20 weeks may not fit at 34. A bralette that stretches and clips lets you tighten or loosen as your shape changes, and it pairs with matching panties if you want a set for photos or the hospital bag.

Postpartum and the weeks after: keep the stretchy pieces

Do not pack away your maternity underwear at delivery. The first weeks after birth often call for the same below-bump or high-waist bands you relied on in the third trimester, especially if you had a cesarean and want nothing pressing on the incision. Stretch lace that adapted to your pregnant shape will also adapt as your body settles.

If you are building a hospital bag, bring two sizes of the same style. Swelling and pad use can change what fits from one day to the next, and having a backup size is easier than doing laundry at 3 a.m.

Decision rules for buying maternity underwear

Rule 1: Buy for now, not for nine months from now: Underwear that fits at 12 weeks will not fit at 36 weeks, and buying ahead usually means guessing wrong. Buy one or two pieces that fit today, then replace when the waistband starts leaving marks. Checkpoint: if you can see a red line on your skin after 30 minutes, size up or change band height.
Rule 2: Choose band height by where you feel pressure: Below-bump bands sit on the hip and avoid belly pressure. Over-bump and high-waist bands spread pressure across a wider area. Neither is universally better; pick based on whether you want the band off your belly or supporting it. Checkpoint: sit, stand, and bend over in the fitting room before deciding.
Rule 3: Prioritize stretch percentage over size number: A style that stretches up to 150% and returns to shape will adapt across trimesters. A rigid band will not, even in a larger size. Read the fabric description, not just the size chart. Checkpoint: if the fabric has no stated stretch, assume it will not grow with you.
Rule 4: For bras, adjustable beats fixed: Ribcage expansion is common in pregnancy, so a bralette with adjustable straps and a back clip gives you room to resize. Wire-free construction avoids pressure points that become more sensitive. Checkpoint: fasten the bralette on the loosest setting first so you have room to tighten later.
Rule 5: Keep two sizes for the hospital bag: Swelling and pad use can change your fit day to day after birth. Packing one size up alongside your current size saves a middle-of-the-night laundry run. Checkpoint: pack both sizes before 36 weeks so you are not scrambling.

Products that fit the trimester rules

Lace Thong - Liquorice Therapy: Lace Thong - Liquorice Therapy is made with signature stretch lace that stretches up to 150% while maintaining support, with a lightweight, soft feel and a smooth, minimal-show finish under clothing. The 150% stretch is what lets one size follow you from early bloating through a growing bump, and the minimal-show finish keeps it invisible under leggings and dresses.
High Waist Thong - Terra: High Waist Thong - Terra is a super high-waisted style in buttery soft lace that is super stretchy but supportive, designed to create a smooth silhouette and stretch up to 150%. The high band spreads pressure across the belly instead of cutting under it, which suits second- and third-trimester days when below-bump bands feel too low.
Lace Bralette - Teal Tide: Lace Bralette - Teal Tide is wire-free and padding-free, made in signature stretchable lace, with a back clip on the elastic band and adjustable straps, and it stretches up to 150%. Adjustable straps and a back clip let you resize as your ribcage expands, and the wire-free build avoids pressure points that get more sensitive during pregnancy.

Who this approach fits

Best for

Anyone in the first trimester who wants to size up gradually instead of replacing the whole drawer
Second- and third-trimester shoppers who want a high-waist band that spreads pressure across the belly
People who prefer a thong silhouette with a smooth, minimal-show finish under leggings and dresses
Anyone whose ribcage has changed and wants a wire-free bralette with adjustable straps and a back clip

Not for

Shoppers who want a single purchase to last the entire pregnancy and postpartum period without any size change
Anyone who needs firm, structured compression or medical-grade support, which these styles are not designed to provide
People who dislike lace against the skin and prefer smooth microfiber or cotton