The amniotic sac is what protects the baby, and the amniotic fluid is what the fluid inside the sac that the baby grows in.
The Amniotic Sac is the sac that contains the baby.
Amniotic sac
It is the amniotic fluid that protects the baby, when the mother goes into labour its the sac that breaks( with the amniotic fluid inside ).
when you go for your 12 week scan you will definitely be able to see a (very tiny) roughly baby shaped baby on the scan congratulations!
fetus
A membranous sac is, as it says, a sac with a membrane. What it is specifically varies. Bronchi in the lungs are membranous sacs and the amniotic sac on a baby is membranous.
Sometimes, it depends on how far along you are. I had a previous miscarriage and I was able to see the baby in the amniotic sac. My sister-in-law had a miscarriage, and she was able to see a very small perfect little baby. So, yes, it is possible to see the baby.l
A uterus is the sac a baby grows in, in its mother's stomach. So a unicorn uterus would be the sac a baby unicorn grows in, in its mother's stomach.
This is the birth sac that needs to be removed so the baby can start to breathe. If you are talking about the sac that shows on an ultrasound, this is the amniotic sac that contains the 'waters' and is absolutely necessary for the growth of the baby. It is the same thing that the answer above mentions.
Some people can see something at 5 or 6 weeks, but usually they can only see the gestational sac at this point. If they do see the baby, it would be very small, since it is only about as big as a grain of rice. Usually you can see the baby pretty well between 8 or 9 weeks, but it still wont really look like a baby. Usually around 10 or 11 weeks is when it actually starts looking human, but everyone is different.
You will likely see the gestational sac and maybe the yolk sac.