A 13-week-old fetus is starting to look more like what you may think of when you hear the word “baby.” That said, the fetus isn’t entirely in proportion. The head is the most noticeable feature at 13-weeks, according to the Idaho Department of Health and Welfare. Even though the head is developing into a more proportional part of the fetus, it’s still roughly one-third of the entire body size.
The pink plus sign pops up on the pregnancy test, and now you’re wondering what’s going on with the little bundle of joy who is growing inside of you. By the end of your first trimester, your baby is developing recognizable features. If you want to paint a mental picture of what a 13-week-old fetus looks like, understanding the major milestones and markers of this time can help you to prep for what you might see on an ultrasound.
Height and Weight
Take a look at your pinky finger. At 13-weeks, your baby is about the same size as it. The fetus is slightly over 3 inches long at this point. Your baby is far from birth weight at 13 weeks. By the time you’re in week 37 of your pregnancy, it’s likely that your baby will be at least 6 pounds.The 13-week fetus weighs in at slightly more than 1 1/2 ounces.
Organs and Control
Even though your baby won't need a diaper for months, her kidneys are making urine by 13 weeks. By this time, the external genitals are developed, according to the U.S. Centers for Disease Control and Prevention. Your baby’s brain continues to grow exponentially by the start of the second trimester. By the time you reach the end of the first trimester your baby is able to coordinate basic actions such as thumb-sucking. At 13 weeks, fetal brain development includes even more complex activities such as rhythmic breathing and the swallowing reflex.
Don’t expect to see open eyes during an ultrasound yet. The 13-week-old fetus’s eyelids are closed to protect your developing baby’s eyes until they open somewhere around week 28. Your fetus doesn’t have teeth yet but does have about 20 buds that turn into baby teeth. The nose is forming, with the bridge visible by 13 weeks.
Muscles and Movement
Whether you’re watching your baby on an ultrasound or you have your hand on your belly, it’s likely you know that a 13-week fetus is capable of movement. You might feel light flutterings of movement, although more pronounced movements typically don't begin until week 16 or later. By this point in your pregnancy, the baby has joints and muscles that let her move. Even though your baby is on the move, the skeleton is still incomplete and continuing to develop.
- Idaho Department of Health and Welfare: Fetal Development
- Baby Center: What Your Baby Looks Like -- 13 Weeks
- WomensHealth.gov: Stages of Pregnancy
- U.S. Centers for Disease Control and Prevention: Fetal Development Chart
- Merck Manuals: Stages of Development of the Fetus
- Zero to Three: Prenatal Development
- Photo Credit herjua/iStock/Getty Images
Development of a 13-Week-Old Baby
When your baby is 13 weeks, or about three months old, he will be experiencing a lot of new developments. You may...
What Does a Baby Look Like at 3 Months in the Womb?
What Does a 13-Week-Old Fetus Look Like? ... During week 12, your baby has progressed to approximately two inches and half an...
The Development of a Two Month Old Fetus
What Does a 13-Week-Old Fetus Look Like? During the 13th week of pregnancy, a baby gains weight and grows rapidly, and some...
About the Fetal Heartbeat
Doctors often use the fetal heartbeat to determine if there is a problem with the growing fetus ... or what is considered...
Development of a Baby Fetus at 6 Months
During these weeks, ... a 6-month fetus measures about 13 1/2 inches long. ... The Development of a Two Month Old Fetus.
Pregnancy Size by Week
Pregnancy Size by Week. ... Weeks 13 to 16--mother has gained about 7 lbs.; ... It takes about 40 weeks from conception...
How Big Is Your Baby at 12 Weeks in the Womb?
At 12 weeks gestation, a fetus is about the size of a small fruit and is beginning to look more like a...
How to Tell Gender on Ultrasounds
One of the most exciting moments in a pregnancy is finding out the baby's gender with an ultrasound at about 18 to...
Stages of Baby Growth During Pregnancy
The baby is starting to look like a baby. At week nine, ... Your baby starts to kick at week 13, and...