Some are premature other wise it genes that run in the family.
Pre-Mes
the baby may be underweight babies
The average birth weight of a normal term baby is around 8lbs therefore a baby born at 3lbs 11oz is significantly underweight
No. Pregnant women who smoke often give birth to underweight babies. Althougt being underweight is probably one of the least problems being born to a smoking mom is likely to cause. They're often late in development, and are also prone to be more restless at night.
some babies are born more developed then others and develop at different stages
No, not all babies have blue eyes when they are born. Some babies are born with very dark eyes.
The hearts of the babies are not properly developed.
Some do...
No, human babies can even hear some sounds in the womb.
Yes, but some have to be born by c-section.
Yes. Some babies are even born with teeth.
There is no such thing as an ugly baby