Pregnancy Shopping Guides Buyer's guide to maternity bras When to buy a maternity bra, and how to find the perfect style and fit in pregnancy 1 of Ad break What is a maternity bra?Think of your everyday bra. Add in extra support, comfortable fabrics, wider straps and extra back length and you’ve got a maternity bra. During pregnancy your ribcage will open making way for your growing abdomen, and your breasts will change in preparation for breastfeeding. In order to keep your breasts looking perky and you feeling comfortable a maternity bra is essential for support and comfort. These days, the term “maternity bra” no longer means giant, plain white over-the-shoulder-boulder-holders. Maternity bras have come a long way – they’re prettier, stylish, patterned and colourful, plus with new technology they offer softer fabrics, an integrated support system and even leave you feeling sexy in your new body. Three everyday maternity bras is a good number to own, but this depends on whether you want varying colours to suit your clothes or crave a luxurious one for those special occasions. Just remember your bra size may change 2-3 times during pregnancy. When should you buy one?A lot of the advice says you should buy a maternity bra in your fourth month of pregnancy, but everyone’s different and some mums-to-be notice an increase in breast size as soon as they realise they’re pregnant. So, whatever stage of pregnancy you’re at, when you start to feel uncomfortable consider buying a maternity bra and then get re-fitted regularly, because you can change a couple of cup sizes throughout pregnancy. In the last couple of months as your ribcage opens further you may just need a back extender to prolong the life of your maternity bra. And, in the last month it might be good to buy a nursing bra as your breasts will be nearing their full size for breastfeeding. What bra size should you buy?Start by measuring the number of inches around your rib cage. Just place the tape measure round your rib cage and under your breasts, making sure it’s flat and straight. Take this number and add 4 to it if it’s an even number, or 5 if it’s an odd number. The result is your band measurement or bra size - the 34-type number of a 34D bra. Once the bra is on you should be able to run a finger comfortably underneath and along the band. Make sure the straps aren’t cutting into your shoulders and ensure the band doesn’t lift up when you raise your arms. While you’ll find this is roughly how the sizing works at big names like Mothercare and Mamas & Papas, there’s no guarantee that all companies follow the same sizing methods. Nothing beats trying a bra on, and if you are buying online, check the site’s sizing guide and that they do exchanges or returns. Finally, consider a back extender - a little strap with hooks and eyes that fit to your existing bra strap, giving you space to breath. It prolongs the life of your maternity bra, especially in the last month or so when your ribcage has fully expanded. What cup size should you buy?To get your cup size, firstly measure in inches around the fullest part of your breasts. Then you need to subtract your band size from this number, and the difference will help you decide your bra size. As a general rule, if your bust measurement is the same as your band size you should look for a cup size A, if it’s 1 inch more try a B-cup and so on. Here’s a quick cup-size guide: 0 difference = A cup 1-inch difference = B cup 2-inch difference = C 3-inch difference = D 4-inch difference = DD 5-inch difference = E 6-inch difference = F 7-inch difference = G Again, this is a general rule and it’s best to try the bra on. You’ll know if the cup size is wrong if your breasts bulge out the top or sides. If this happens, go up a cup size. But, if the cups are saggy but the back fits you may need to go down a cup size. It’s trial and error, but as long as most of your breast is covered (depending on the style) you should be fine. It’s also worth heading in-store to get fitted –many retailers that sell bras will offer a bra fitting service. Continue slideshow > Should you avoid underwire maternity bras?Some health professionals advise against underwire bras in pregnancy because they think they are restrictive and can suppress the milk ducts. However, there doesn’t seem to be any concrete evidence to prove this and views have changed. As long as your bra fits well it should be fine. Also, with new technology, wire has been replaced by light boning, which is great for larger-breasted women who don’t want to lose the support of an underwire. For many women though the back strap should be wide enough to support you without the need for wiring. What should you wear at night?For some mums-to-be taking your bra off might mean more pain or discomfort. Some of you might even experience leakage in your last trimester and need to wear breast pads. If this is the case, there are night-time bras. These are usually softer, lighter and seam- or hook-free. These are more popular in the third trimester when breast size has reached its peak, but it’s up to you to decide what’s comfy. Many night-time bras are made of super soft cotton for extra comfort, and might have a hook that allows for breastfeeding so you can wear it post-pregnancy, too. Some daytime bras are so comfortable you can wear them at night, so look out for these as a great money saver. Where do you start?Before you start shopping, check out our in-depth reviews of maternity bras to discover what other mums-to-be have to say. By Zoe West Comments Latest on MadeForMums The 12 BEST things about being pregnant Mum's 'overweight' post-baby pic: 'My body can wait. 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