Isaac's little brother or sister?

I had my first ultrasound on Monday and everything is great. It was nice to hear that from the nurse when she was doing it. She kept on saying things look great and the doctor confirmed the baby is growing exactly how he/she should be and healthy.
And to show how much he/she is growing, the baby is measuring at 19 1/2 weeks where I am really only 18 weeks on Friday. I know it really doesn't mean that much but it kind of does for me because the doc doesn't want me to go over my due date--fearing the baby will be too big to deliver safely. I guess I'm that small inside and basing it off Isaac being so long and lean. The baby would run out of room. I just trust my doctor and hoping that the 2nd delivery can be like the first...well maybe a little bit faster with less pain. Ha!

As far as the sex, there's a 50% chance it will be a girl! We did not find out the sex. BOTH of us did not find out the sex. I wasn't going to but Nick wanted to. And up until we got in the room, he was going to but all of a sudden he told the nurse we didn't want to know the sex. I was shocked. For those who don't know, Nick hates surprises and didn't want to start liking them this way. I'm really proud and happy that he didn't.
But...I think it's a boy. I think I saw something that indicated that when she said to look away and just have a feeling. But I also thought Isaac was going to be a girl. So, maybe I will be wrong.
All pregnant women say, so here it goes...I just want the baby to be healthy. One minute I think a boy will be easy because we know what to expect but as a mom, you want a little girl. If it's not then my niece Maren will get the mani/pedi's, shopping and do the girl stuff with me!