maternity clothes advice

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Please can someone give me advice on maternity clothes. I'm now 20 weeks pregnant and I'm a first time mum. I've started to wear leggings but I do like to wear a pair of jeans and mine are starting to get a little tight. 
If I buy a size 12 pair of maternity jeans will they grow with my bump or will I need to buy another pair when I get bigger? I don't have a clue 😩