40-Weeks

The beginning:

6-week ultrasound
 From What to Expect When You're Expecting
"Your baby's jaw, cheeks, chin, eyes, ears, and nose are beginning to form what will eventually become one adorable face. In addition, her kidneys, liver, and lungs are developing, and her heart is now beating 80 times a minute (and getting faster every day). All this and she's still no bigger than the length of a nail head (about a quarter of an inch) from crown to rump!"

7-week ultrasound
 From What to Expect When You're Expecting
"Your baby is now about the size of a blueberry (and about 10,000 times bigger than he was at conception). Most of that growth is concentrated in the head as new brain cells are generated at the rate of 100 per minute. Your baby's mouth and tongue are forming as arm and leg buds sprout, and those little kidneys are getting ready to do their job (pee production and excretion)."

Mid-point:

From the outside

20-week ultrasound

 From What to Expect When You're Expecting

"If you're having a girl, her uterus is now fully formed and her ovaries are holding about seven million primitive eggs. If you're having a boy, his testicles have begun their descent from the abdomen to their ultimate destination — the scrotum. And while your baby is definitely getting bigger (weighing in at about ten ounces and measuring six and a half inches), there's still plenty of growing room in there, which allows him to twist and turn (and allows you to feel his acrobatics!). "


Home-stretch (Third trimester):

27-weeks

The baby is size of cauliflower or a large snow-cone this week 

  From Babble Pregnancy week-by-week guide
 "This week, your little one weighs in at almost 2 pounds and is almost 15 inches long. Eyelashes are also starting to grow at the ends of the lids, and someone will be taking a first peek around this week, as baby's eyelids flutter open for the first time. The eyelids won't stay open for too long yet, but the blinking reflex will begin."

 28-weeks (From the outside- obviously)
From Babble Pregnancy week-by-week guide
"Baby will be getting some color this week — eye color, that is. Pigment will fill in your baby's irises, but it might take six months after he/she is born for the eyes to settle in to their true color. Eyelashes, eyebrows and hair are continuing to grow, and brain tissue is rapidly increasing. You'll also be happy to know that your baby is plumping up as more much-needed body fat develops (one step closer to those adorable baby thigh rolls and Buddha belly), even though he/she still only weighs 2 ½ pounds."

30-weeks

From Babble Pregnancy week-by-week guide

"Your baby's brain is expanding by the day, taking on new functions like temperature regulation. This week, the brain is starting to get that wrinkly, indented look, which will help the brain tissue expand as the baby develops into adulthood. Besides the brain, your baby's body is continuing to grow — now at just over 3 pounds and 17 inches long."

 36-weeks

From What to Expect When You're Expecting

"Your little one is now about six pounds in weight and measures slightly more than 20 inches in length. Growth will slow down now in preparation for birth, so your baby will be able to fit the narrow passageway to the outside and so he or she can store up the energy needed for delivery."