can you see a pattern?

Not just the pattern on the dresses (it was the 70's) but another pattern??

I posted this photo a few weeks ago. Apart from working out that it wasn't Shirl's wedding we can't really narrow it down - other than we think Mum might have been pregnant with Jojo - maybe - which would place it somewhere around 1975. We know it is after 73 because mum is wearing a wedding ring. Dad is no help at all - as this was obviously a family gathering on my Mum's side, Dad would have just tagged along - in a totally loving way of course because Dad likes hanging out with Mum's family. My mum is from a family of 14 - 12 girls and only 2 boys. Mum was around the middle. This is a photo of the sisters with their dad - my poppy. p>

Can you see the pattern I speak of? As a hint it may have something to do with why I constantly have to go to the gym...

PS My Mum is in the back row - the purple dress and beside her is my Aunty Shirl. My Aunty Ivy is in the front row - pink dress beside poppy