Quite often an increase in your bust size is the first sign that you are pregnant. It is very important that you take good care of your breasts during your pregnancy as they will become heavier and fuller. They have no muscles, only ligaments which can be overly stretched if not properly supported. During the nine months of your pregnancy and whilst breastfeeding they can gain up to 500 grammes or more in weight (that's half a bag of sugar) and may become sore and tender.
The ideal time to buy a maternity bra is at around 16-18 weeks as this is when your cup size will usually have increased to its maximum for the duration of your pregnancy. It is also the time when your ribcage will start to expand ready to accommodate your growing baby. Most women increase 1 full size in both the cup size and the rib band of their bra during their pregnancy. Eg. If you were size 34C prior to being pregnant, you will grow to size 36D during your pregnancy.
When you buy your maternity bras at this time (16-18 weeks), it is essential that they feel comfortable around your ribcage on the tightest hook at the back. This way you have another two or three hooks to grow into during the next few months. Ensure that the fabric of the cup fully covers your breast and feels supportive. It should feel snug but not tight under your arms.
A good maternity bra, if properly fitted, will last for the whole of your pregnancy. It is an essential investment and you should not need to buy any further bras in different sizes. Wearing badly fitted bras can make you feel uncomfortable around your ribs and shoulders, leave red marks and chafing, and could possibly lead to long term back pain and problems with your posture.
A great buy, at 16-18 weeks, is the Bravado Body Silk Seamless Maternity & Nursing Bra as it will last throughout your pregnancy and you can continue to wear it after the birth of your baby for nursing. This is the only bra (that we know of) that is properly designed to fit for both. It has a huge celebrity following and fits up to F cup whilst breastfeeding so if you are D cup or less prior to being pregnant, it is your perfect investment. You could be wearing it for 1 - 3 years!
If you have a larger bust and need more help, then consider the Anita Underwired Maternity Bra. It is the perfect choice if you usually wear underwire bras as it has soft natural shaping which is extremely comfortable and safe to wear throughout your pregnancy but also offers incredible support up to H cup.