Any ideas what was wrong with my placenta?

When I was pregnant with my daughter I was so small and I only gained 18 lbs. When she was born she weighed 8 lbs 3 oz. She was born with congenital motor nystagmus and severe acid reflux. Later on she walked late and had gross motor delays. She is now doing great and you very rarely notice any nystagmus. My wonder now that I am pregnant with my second child is why when I gave birth to my daughter was my placenta so small. I didn't open my eyes to see it but I could feel it was small and my mother saw it and said it was about the size of a softball and was brown and dried out looking. I was only one day over my due date with her. Any ideas what would cause the placenta to get this way since I don't want it to happen with this baby and possibly cause problems. During this ultrasound I had they said the placenta looked nice and healhty so thats good. I don't know when I was pregnant with my daughter if the placenta was small then or if it happened towards the end of my pregnancy more. When my daughter came out her body was sooo swollen and red her cheeks were huge and she just looked painful she was so swollen. No one ever said anything about it and I wonder what went on.