Second Trimester Ultrasound Pictures

Fetal Size: Length, 3 1/4 to 4 inches, crown to rump; weight, around 1 ounce

Fetal Development Milestones: Male or female genitalia are now formed. Baby's liver and spleen are producing red blood cells. Also, his or her upper limbs are proportionate to the rest of the body. The lower limbs are slightly shorter.

What You're Seeing: The sonographer has magnified the image to show the baby-to-be's profile. His head is on the right-hand side of the image and his hand is on his chest.

Fetal Size: Length, 4 to 4 1/2 inches, crown to rump; weight, 1 3/4 ounces

Fetal Development Milestones: Baby's skeletal system is continuing to develop. Characteristic hair patterns on the scalp are taking shape.

What You're Seeing: In this 3D image, the baby-to-be is curled up, her hands covering her face (she's about the size of a grapefruit). The large bones that make up her skull are forming and hardening. As they harden, the bones appear whiter and brighter in the image. These cranium pieces do not come together until well after birth.

Fetal Size: Length, 4 1/3 to 4 2/3 inches, crown to rump; weight, 2 3/4 ounces

Fetal Development Milestones: Baby's lower limbs are now well developed. Toenails are forming and your baby's eyes and ears continue to move into the proper place. Facial muscles are beginning to work.

What You're Seeing: In this closeup view of Baby's profile, you can see how his facial features are becoming more defined. Notice that the sonographer has measured the length of his nasal bone. This specialized measurement may be useful in screening for some genetic abnormalities.

Fetal Size: Length, 4 1/2 to 4 3/4 inches, crown to rump; weight, 3 1/2 ounces

Fetal Development Milestones: Fetal bones are becoming more visible on ultrasound. You may be able to feel some fetal movement, particularly if you have been pregnant before.

What You're Seeing: This close-up shows the baby-to-be's tiny right hand. You can see each bone within her delicate fingers. Although she may not be coordinated enough now to use her fingers (other than to wiggle!), by the time she's born she will have matured to the point where her fingers will have some dexterity—she'll even be able to grasp your finger with her hand!

Fetal Size: Length, 5 to 5 1/2 inches, crown to rump; weight, 5 1/4 ounces

Fetal Development Milestones: Your little one's ears are becoming more shapely. Facial features are now in their proper position. Baby's eyes are now developed enough to detect light.

What You're Seeing: Halfway through your pregnancy (18-20 weeks) your health care provider may request an ultrasound to evaluate your baby's size and anatomy. This image shows a cross sectional view of baby's head. The sonographer will measure baby-to-be's head circumference or biparietal diameter (BPD).

Fetal Size: Length, 5 to 5 1/2 inches, crown to rump; weight, 5 1/4 ounces

Fetal Development Milestones: Facial features are now in their proper position. Baby's bones continue to harden.

What You're Seeing: This image shows a cross sectional view of the baby's abdomen at the level of the stomach. The distance around the baby's abdomen, or abdominal circumference, is being measured.

A complete standard second trimester ultrasound includes images of your baby's chest, abdomen, and brain. The sonographer will also take measurements to evaluate your baby's growth.

Fetal Size: Length, 5 to 5 1/2 inches, crown to rump; weight, 5 1/4 ounces

Fetal Development Milestones: Bones and nerve endings associated with hearing are developing. Baby's soft bones are beginning to harden too.

What You're Seeing: In this image, the sonographer has marked the length of the femur (the thigh bone). From this measurement, the sonographer can evaluate your baby's growth. In the image on the right, you can see the bones of both of the baby's lower legs.

Fetal Size Length, 5 to 5 1/2 inches, crown to rump; weight, 5 1/4 ounces.

Fetal Development Milestones: If you're having a girl, her ovaries are developed.

What You're Seeing: A little girl! Determining your baby-to-be's gender isn't always easy. In this image, looking between Baby's legs, the sonographer can identify labia. Baby doesn't always cooperate during an ultrasound exam, but here, there's no mystery.

Fetal Size: Length, 5 to 5 1/2 inches, crown to rump; weight, 5 1/4 ounces

Fetal Development Milestones: Male genitalia continue to form.

What You're Seeing: It's a boy! In this image, it's almost as if the baby is sitting down, legs apart, so that his gender is clearly visible. The sonographer can't always determine a baby's sex during an ultrasound exam (and, of course, the exam is centered on the health of the fetus, not his gender). But here, you can see the baby's penis in the center of the picture.

Fetal Size: Length, 5 1/4 to 6 inches, crown to rump; weight, 7 ounces

Fetal Development Milestones: Arms and legs are now well-developed and in proportion.

What You're Seeing: Your baby's legs and arms are continuing to develop and add muscle. You may be able feel your baby's movements now, or within the next week or two.

Fetal Size: Length, 5 2/3 to 6 1/2 inches, crown to rump; weight, 9 ounces

Fetal Development Milestones: Hair and nails are continuing to grow. In girls, the uterus is now formed and the vaginal canal is also forming. You can feel fetal movements even more now!

What You're Seeing: Here, the baby-to-be is curled up with her leg tucked in and her arms covering her face, which is turned away. She may look scrawny now, but developmentally she's right on track. Her bones, visible in this 3D image, are continuing to harden and develop.

Fetal Size: Length, 7 1/4 inches, crown to rump; weight, 10 1/2 ounces

Fetal Development Milestones: Baby is swallowing amniotic fluid. Bone marrow is beginning to produce red blood cells. Baby moves and wiggles frequently.

What You're Seeing: This profile image not only shows how your baby-to-be's bones and skeletal structures are forming, but also his lungs. Looking at his chest, the sonographer can identify the heart and lung tissue.

Fetal Size: Length, 7 2/3 inches, crown to rump; weight, 12 1/4 ounces

Fetal Development Milestones: Baby's hair may be growing, and eyebrows are beginning to form. Her sense of taste and smell are developing too.

What You're Seeing: Here, the baby-to-be appears to be sleeping (babies in utero do have periods of sleeping and periods of activity).

Fetal Size: Length, 8 inches, crown to rump; weight, almost 1 pound

Fetal Development Milestones: Baby-to-be is adding fat tissue and gaining weight. Rapid eye movements (REM) are now beginning.

What You're Seeing: With the baby-to-be crouched and his legs pulled in toward his chest, you can almost see his complete profile. Images of the baby's entire body are difficult now that he's more than 8 inches in length. He's about to experience a dramatic weight gain in the coming weeks. For now, he's still relatively thin.

Fetal Size: Length, 8 1/2 inches, crown to rump; weight, 11/4 pounds

Fetal Development Milestones: Baby-to-be is capable of reacting to noise with a blink-startle response. Her lungs are developing.

What You're Seeing: The image on the left shows a magnified view of the four chambers of the baby-to-be's heart. The image on the right show's blood flowing from the upper chambers of the heart (the atria) into the lower chambers of the heart (the ventricles). The walls of the ventricles are more muscular than the atria, because they have to pump blood to the baby's lungs and the rest of the body.

Fetal Size: Length, 8 3/4 inches, crown to rump; weight, 1 1/2 pounds

Fetal Development Milestones: Baby-to-be's hearing has developed enough to hear Mother's voice. Hair is continuing to grow on the head.

What You're Seeing: This close-up image of your baby-to-be's ear shows just how developed her features have become. Although her hearing is still rudimentary, by the time she's born she'll be able to recognize your voice from hearing it constantly in utero.

Fetal Size: Length, 9 1/4 inches, crown to rump; weight, nearly 2 pounds

Fetal Development Milestones: Baby's eyelashes are forming and her scalp hair continues to grow.

What You're Seeing: Hi, Mom! This image reveals a close-up look at your unborn baby's nose and mouth. It's almost as if his face is pressed up against a window.

Fetal Size: Length, 9 2/3 inches, crown to rump; total length about 15 1/4 inches; weight, 2 pounds

Fetal Development Milestones: Lungs are continuing to develop, and the liver is maturing. Baby's immune system is strengthening.

What You're Seeing: Now that the baby-to-be is growing rapidly, it's harder to get a complete profile in the womb (she just doesn't fit in the picture anymore!). Even though she has more than tripled her weight since this trimester began, there's still plenty of growing left to do. This week marks the end of the second trimester—just one more trimester to go!

All ultrasound images for this slideshow 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.

Finished with your second trimester? Click here for additional prenatal ultrasounds and information:

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