Third Trimester: Images of Your Developing Baby

Welcome to your third (and last) trimester! Keep clicking for a week-by-week look at your baby's development in the womb.

Fetal Size: Length, 10 inches, crown to rump; total length 15 3/4 inches. Weight, almost 2 1/2 pounds.

Fetal Development Milestones: Your baby now has added brain tissue and her scalp hair continuing to grow. Her eyes are opening and she's gaining weight.

What You're Seeing: Your baby-to-be's hair is seen waving in the amniotic fluid. This hair is called lanugo. Unfortunately, we can't predict how much hair your baby will have because he will lose his lanugo before being born and it will be replaced with the hair we're used to seeing on infants at birth.

Fetal Size: Length, 10 1/2 inches, crown to rump; total length 16 3/4 inches. Weight, 2 3/4 pounds.

Fetal Development Milestones: Your little one's muscles are maturing. She'll continue to gain weight over the coming weeks.

What You're Seeing: This week, your baby-to-be's bones are hardening, and her muscles strengthening. In fact, you may have noticed from her kicks and jabs that she's growing stronger each week. Bones appear bright white on a sonogram. Although you can't see it in this image, your baby has probably been practicing his breathing movements this week, though his lungs still need more time to mature.

Fetal Size: Length, 10 3/4 inches, crown to rump; total length 17 inches. Weight, 3 pounds.

Fetal Development Milestones: Baby's eyes are opening and she's gaining weight.

What You're Seeing: This image shows how developed your baby-to-be's features have become. With her pouty lips and tiny nose, she looks much like she will at birth. Note the baby's hand in front of her eyes and forehead.

Fetal Size: Length, 11 3/4 inches, crown to rump; total length almost 18 inches. Weight, 3 1/2 pounds.

Fetal Development Milestones: Baby continues to develop as he or she gains weight.

What You're Seeing: This image gives a close-up view of the lower end of your unborn baby's spine. You can see the spinal cord protected by the bright white bones of the spine.

Fetal Size: Length, 11 1/2 inches, crown to rump; total length 19 inches. Weight, 4 pounds.

Fetal Development Milestones: Baby's toenails are now formed, he's practicing his breathing, and he's continuing to gain weight and grow.

What You're Seeing: There's not much to report on your baby-to-be's developmental milestones this week. Much of his growth is strictly adding weight through fat layers that will insulate his maturing organs. He'll need plenty of fat tissue to keep him warm once he leaves his home in your womb and enters the world, where the environmental temperature is not as controlled. Although you can't see it in this image, your baby has probably been attempting to breathe this week, though his lungs still need more time to mature. Another development you'll notice in this image -- look closely and you might spy the edges of his toenails, which are now fully formed.

Fetal Size: Length, 12 inches, crown to rump; total length 19 1/2 inches. Weight, 4 1/2 pounds.

Fetal Development Milestones: Your baby is getting more plump each day.

What You're Seeing: Your baby-to-be's brain is continuing to grow and develop. In this image, the red and blue show blood flow to the part of his brain that lets the two halves of the brain communicate with one another.

Fetal Size: Length, 12 3/4 inches, crown to rump; total length 19 3/4 inches. Weight, 5 pounds

Fetal Development Milestones: Baby's lungs are continuing to mature and she's continuing to gain weight.

What You're Seeing: In this image of a profile, the baby's mouth is open. She may be drinking amniotic fluid or taking it into her lungs, which aids in the development of her respiratory system.

Fetal Size: Length, 13 1/4 inches, crown to rump; total length 20 1/4 inches. Weight, 5 1/4 pounds.

Fetal Development Milestones: Baby's kidneys are fully developed and his liver is functioning. He continues to add weight.

What You're Seeing: This closeup shot of your baby-to-be's ear shows how fully developed his facial features have become. He now looks like the newborn that you'll be welcoming into the world in a few weeks (only five more to go!). Your baby is also maturing on the inside too. He continues to practice his breathing movements, which move amniotic fluid in and out of his lungs to aid in their development.

Fetal Size: Length, 13 1/2 inches, crown to rump; total length 20 3/4 inches. Weight, 6 pounds.

Fetal Development Milestones: Not much to report this week! Baby continues to gain weight.

What You're Seeing: This image of your baby-to-be's face looks identical to the profile you'll be seeing in person in a few weeks (four or less!). For the remaining weeks, your baby will be adding 1/2 pound each week until birth.

Fetal Size: Length, 14 inches, crown to rump; total length 21 inches. Weight, 6 1/2 pounds.

Fetal Development Milestones: Your baby is officially full term!

What You're Seeing: Sometimes your doctor or midwife will ask for a test to check how well your baby is doing. One indicator of your baby-to-be's well being is a measurement of the amniotic fluid. This can also be part of a test called a biophysical profile, which will also include watching the baby's various movements. In this image, the sonographer is measuring the deepest pocket of fluid in each of four areas of your uterus. As you can see, your baby is getting a bit crowded in there!

Fetal Size: Length, 14 inches, crown to rump; total length 21 inches. Weight, 6 3/4 pounds.

Fetal Development Milestones: All of Baby's major body systems are working, and she's continuing to practice breathing in utero. Her movements will lessen as she runs out of space.

What You're Seeing: During the last few weeks of gestation, your baby has less and less room to move. A few weeks (and pounds) ago, she may have been kicking and wiggling constantly; now she simply doesn't have enough room. If you or your health care provider have any concerns about your baby's development, especially if her movement becomes too infrequent, you may have an ultrasound to check up on her. This image shows the results of monitoring a baby's heart rate in utero. At the top, the baby's heart beats; below, the lined measurements track and then determine baby's heart rate to make sure it's within the normal range.

Fetal Size: Length, 14 1/2 inches, crown to rump; total length 21 1/2 inches. Weight, around 7 pounds.

Fetal Development Milestones: Delivery day is coming soon!

What You're Seeing: What you're seeing: The sonographer is getting a 3/4 view of your baby-to-be's face?and you can actually see her eyelashes! Your health care provider may want to see if the baby has settled into a head-down position?the best position for a normal delivery.

Fetal Size: Length, 14 3/4 to 15 1/4 inches; total length 21 1/2 inches. Weight, 7 1/2 pounds.

Fetal Development Milestones: Delivery day!

What You're Seeing: If your healthcare provider wants to get an idea of your baby's weight, one of the most important measurements the sonographer can take is the abdominal circumference. This image is a cross section of your baby's belly. The small back oval is her stomach, and the curved black line is the blood vessel that brings nutrients from the placenta. Soon, you'll have a very different way of feeding her!

Copyright &copy 2009 Meredith Corporation.

All ultrasound images were provided by the sonographers of the Johns Hopkins Maternal-Fetal Diagnosis and Treatment Center. We are grateful to Christine Bird, BS, RDMS, RVT, chief obstetrical sonographer, and Jude Crino, M.D., medical director, for their assistance with this project.

For examples of prenatal ultrasounds and more information on your baby's fetal development, be sure to visit www.aium.org and www.marchofdimes.org.

For more fetal ultrasounds, be sure to read:

For more information about ultrasounds and fetal development, check out the following resources: