Pregnancy is an exciting time filled with lots of milestones and markers. Your baby is growing and developing at a rapid pace. Here’s an overview of what the little one is up to during each week.
Keep in mind that height, weight, and other developments are only averages. Your baby will grow at their own pace.
Weeks 1 and 2
Though you aren’t pregnant in weeks 1 and 2, doctors use the start of your last menstrual period to date your pregnancy.
The follicles on your ovaries are developing until one or two dominate and are released during ovulation. This occurs around 14 days after the start of your period.
Conception occurs at the beginning of week 3 — after ovulation — when your egg is released and fertilized by the father’s sperm. After fertilization, your baby’s sex, hair color, eye color, and other characteristics are determined by chromosomes.
Your baby has just implanted in your uterine lining and is now a tiny fetal pole around 1/25-inch long. Their heart is already forming along with arm and leg buds, brain, and spinal cord.
To get an idea of your baby’s size, look at the tip of a pen. The embryo now has three layers. The ectoderm will turn into their skin and nervous system.
The mesoderm will form their bones, muscles, and reproductive system. The endoderm will make up the mucous membranes, lungs, intestines, and more.
By week 6, your baby’s heartbeat can usually be detected as a fast flicker on an ultrasound.
Your baby’s face is slowly getting some definition this week. Their arms and legs look like paddles, and they’re a little bigger than the top of a pencil eraser.
Your baby has now graduated from embryo to fetus, and is an inch long from crown to rump, and weighs less than 1/8 ounce.
Your baby’s heart is beating regularly, their fingers and toes are sprouting, and their head and brain continue to develop. Soon their organs will be working together.
Boy or girl? Your baby’s genitals are beginning to develop this week, though you won’t be able to detect the sex on an ultrasound yet.
Your baby is about 2 inches long and weighs 1/3 ounce. Most of the length and the weight are in the head.
You baby is 3 inches long and weighs about 1 ounce. Their vocal cords are beginning to form, and their kidneys are now functioning.
Welcome to the second trimester! Your baby has started urinating in the amniotic fluid, and their intestines have moved from the umbilical cord to their abdomen. The riskiest part of your pregnancy is over, and your chance of miscarriage has dropped to only 1 to 5 percent.
Your baby weighs approximately 1 1/2 ounces, and their crown to rump length is about 3 1/2 inches.
If you have an ultrasound at week 15, you might see your baby’s first bones forming.
Your little one is 4 to 5 inches long from head to toe and weighs around 3 ounces. What’s happening this week? They’ve started making sucking motions with their mouth.
Fat stores that will keep your baby warm and give them energy are accumulating beneath the skin. Your baby weighs 7 ounces and stretches 5 1/2 inches from crown to rump.
This is a big week for your baby’s senses. Ears are developing, and they may start hearing your voice. Their eyes may start to detect light.
You might wonder how your little one’s skin will fare in the amniotic fluid for so long. This week, vernix caseosa is coating their body. This waxy material serves as a protective barrier against wrinkling and scratching.
Talk to your baby. This week they’ll start to hear you! Your baby weighs around 9 ounces and has grown to a whopping 6 inches long. By now you should be able to feel kicking inside your womb.
Your baby can now swallow and has fine hair called lanugo covering most of the body. By the end of this week your baby will be about 7 1/2 inches from crown to rump and weigh a full pound.
Although your baby still has a lot of growing to do, ultrasound photos will start looking more like what you might imagine a baby to look like.
You will likely feel lots of kicks and jabs at this stage as your baby experiments with movement in their extremities. Babies born at 23 weeks can survive with months of intensive care, but may have some disabilities.
Now your baby is 1 foot long from head to toe and weighs 1 1/2 pounds. Their taste buds are forming on the tongue and their fingerprints and footprints are nearly complete.
Your baby’s startle reflex is now developing. You may also notice that they have specific rest and active times.
Your little one is approximately 13 inches from crown to rump and weighs just less than 2 pounds. Your baby’s hearing has improved to the point that they might recognize your voice. For fun, try singing or reading to them.
Your baby’s lungs and nervous system continue to develop this week. Now is a great time to track your baby’s movements. If you notice a decrease in movement, call your doctor.
You baby’s brain is starting to develop this week. Deep ridges and indentations are forming, and the amount of tissue is increasing.
You’re in the home stretch! At the start of your third trimester, your baby is 10 inches from crown to rump and weighs a little over 2 pounds.
Your baby weighs 3 pounds and has grown to 10 1/2 inches this week. Their eyes are now open during their waking hours and their bone marrow is collecting red blood cells.
Your baby is 15 to 17 inches from head to toe and tips the scales at about 4 pounds. The eyes can now focus, and reflexes like thumb sucking are probably starting to occur.
Your baby has a great chance of survival with medical assistance if born after 32 weeks. Their nervous system has developed enough to regulate their body temperature.
You probably know your baby is sleeping a lot, but did you realize that they might be dreaming? It’s true! Their lungs have also matured almost completely by this point.
Your baby is about 17 inches long from crown to rump. Their fingernails have grown all the way to their fingertips, and the vernix is getting even thicker than before.
Now begins your baby’s most rapid weight gain stage — up to 12 ounces each week. Right now, they’re around 5 pounds, 5 ounces. Most of their fat is depositing around the shoulders.
Your baby is an impressive 17 to 19 inches long from head to toe and weighs 5 to 6 pounds. They’re running out of space in your uterus, so they may move around slightly less than normal. Speak with your doctor about counting kicks to assess fetal health.
Your baby is now gaining about 1/2 ounce in fat stores each day. And your baby’s major organs are ready to work outside the womb.
By week 38, baby is over 18 to 20 inches long and weighs approximately 6 pounds and 6 ounces.
Congratulations! Your baby is officially full term.
Week 40 and Beyond
Most babies born at 40 weeks are about 19 to 21 inches long and weigh between 6 and 9 pounds.
Boys typically weigh more than girls. Keep in mind that only 5 percent of babies are born on their due dates. Don’t be surprised if you deliver a few days or even a week or so earlier or later than your due date.
No matter where you are in your pregnancy, there’s something interesting going on.
Remember, your doctor is always your best resource regarding your pregnancy and your baby’s health. If you have any concerns about development, jot down your questions to bring to an upcoming appointment.