Week 33 Ultrasound: What It Would Look Like

Exciting news: your baby is in his final stages of development when you're 33 weeks pregnant! Find out exactly what to expect during this part of the journey.

By Laura Riley, M.D.

and Kristen J. Gough

Published on April 19, 2010

During these final weeks of pregnancy, your baby enters his "finishing period." This is exactly what it sounds like: Your baby's organs, skeleton, and body are well formed, but he needs a little more time to finish getting ready to take on the world. By now he weighs a good 4-1/2 pounds and measures more than 17 inches long, pushing the height of your uterus nearly to your rib cage. His toenails have completely grown in, as has any hair on his head.

Your amniotic fluid level is at its highest about now. The placenta is still providing oxygen to your baby through the umbilical cord, but your baby is practicing his breathing regularly, swallowing amniotic fluid as he opens and closes his mouth and exercising his diaphragm muscle. He continues to store iron in his liver, and the connections between his brain cells keep spreading like tiny tree branches. Neurons and synapses are developing between those brain cells, forming connections so that he'll have the skills to thrive as an infant.

At this stage, an ultrasound can offer your health care provider (and you) a thorough look inside the womb in the weeks leading up to your delivery. If your provider has any concerns about your baby's health or your pregnancy, she might request that you have a biophysical profile (BPP). A BPP is an evaluation of your unborn baby's well-being, using an ultrasound examination and a non-stress test.

The ultrasound portion of a BPP includes four parts. Over a period of 30 minutes, the sonographer looks for:

Fetal breathing movements. Looking closely at your unborn baby's lungs, the sonographer will confirm breathing motions by watching lung movements.
Body movements. The sonographer will watch for your unborn baby to move his body, head, arms, and legs.
Fetal tone. At this stage in development, your unborn baby should be able to extend or flex his arms, legs, and fingers. Your sonographer will look for your baby to make these movements.
Amniotic fluid. By taking various measurements of the dark spaces on the ultrasound image, the sonographer can determine how much amniotic fluid volume is within the uterus. These fluid levels need to be within a certain range; decreased fluid levels could indicate a problem with the pregnancy.

Terms to Know

Biophysical profile (BPP): An in-depth evaluation of a fetus' well-being using ultrasound imaging and a non-stress test to look for indications of fetal distress or difficulties in a woman's pregnancy.