Exercise would normally be done to get/stay in shape
Exercise while pregnant has a completely different purpose
Unless you are a freak of nature, working out wont help you stay skinny if you're growing a human
In my case, it doesn't matter how much I work out...there is still a 9month race between my belly and my butt
Your body will (hopefully) be storing fat for nursing a baby
I ran 2 miles a day until 36 weeks with izzy and still gained 35 lbs
I didn't work out hardly at all with reed and gained 18 but was sick and miserable and had horrible back problems.
Exercise during this time in your life has a different purpose
It helps your body adjust to the rapid changes
It helps you not have so many aches and pains
It helps labor (or so I've been told)
It helps you get back to pre-pregnancy shape after your sweet little one is born
It helps keep you healthy and actually gives the baby a workout while its in your belly
So even though it seems pointless to do jumping jacks and squats because you're still going to gain weight (hopefully) you need to get moving as many days a week as possible. Your postpartum body will thank you.
Enjoy your new curves.
And if you're super lucky like me, your husband will love them. The 3 Bs of a sexy pregnant lady: boobs butt and belly