Fetal development timeline

Fetal development timeline

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The transformation from a tiny fertilized egg to a fully formed baby is awe-inspiring. Here's a look at the major milestones babies in utero typically reach, from conception to birth, and approximately when they happen.

First trimester

3 weeksYour baby-in-the-making is a ball of cells called a blastocyst. The blastocyst already contains a full set of DNA from you and your partner, which determines sex, eye color, and other traits.
4 weeksThe ball of cells has officially become an embryo and is about the size of a poppy seed. Over the next six weeks, all of your baby's organs will begin to develop, and some will start to function.
5 weeksYour baby's tiny heart begins to beat – at twice the rate of yours. His entire "body" is only about the size of a sesame seed.
6 weeksFacial features (like eyes and nostrils) are beginning to form, and little buds appear where arms and legs will develop.
8 weeksArms and legs are growing, and your baby now has little fingers, as well as a nose and upper lip. He's moving quite a bit now, but you won't feel it. He's about 5/8 of an inch long and weighs hardly anything – four-hundredths of an ounce.
9 weeksEyes have developed, though your baby's eyelids are fused shut for now. She's lost her "tail" and is starting to look more human.
10 weeksThe embryo has become a fetus. His vital organs – such as kidneys, intestines, brain, and liver – are starting to function. Tiny fingernails and toenails are starting to form.
11 weeksYour baby is almost fully formed. Her bones are beginning to harden, and her genitalia are developing externally. She can hiccup, though it's too soon for you to feel it.
12 weeksYou can hear your baby's heartbeat at a prenatal checkup.(You may already have heard it at an early ultrasound.) Your baby's just over 2 inches long and weighs about half an ounce.

Second trimester

14 weeksYour baby's kidneys are producing urine, and he releases it into the amniotic fluid. He can make facial expressions and may have discovered thumb-sucking.
15 weeksYour baby can see light that filters in from outside your womb, even though her eyelids are still shut.
16 weeksYour baby's sex may be detectable at your mid-pregnancy ultrasound, which typically happens between 16 and 20 weeks.
18 weeksIf you haven't felt your baby move yet, you probably will in the next few weeks. It'll take a couple of weeks longer for other people to feel your baby's movements from the outside.
19 weeksYour baby can hear your heartbeat and sounds that come from outside your body, such as your partner's voice. Her skin is wrinkly and is covered by a protective, waxy coating. She measures about 6 inches from head to bottom and weighs about 8 1/2 ounces.
23 weeksYour baby's sense of movement has developed, so he can feel the motion if you dance. His sense of hearing continues to improve. You may sometimes be able to see him squirming under the surface of your belly.
24 weeksYour baby's taste buds are developing. Her brain is growing very quickly, and her hair may be growing, too. She's almost a foot long and weighs just over a pound.
27 weeksYour baby's lungs are developing but won't be fully functional for several more weeks. He's "practicing" for life on the outside by inhaling and exhaling amniotic fluid, sleeping and waking up at regular intervals, opening and closing his eyes, and sucking his fingers.

Third trimester

28 weeksYour baby may be dreaming. She has eyelashes, and her eyesight is improving. Billions of neurons are developing in her brain. She weighs about 2 1/4 pounds and is about 15 inches long, head to heel.
32 weeksHe's grown cute little fingernails and toenails. Your baby is also starting to plump up in preparation for birth. He's almost 17 inches long (head to heel) and weighs about 3 3/4 pounds.
34 weeksYour baby's lungs and central nervous system are continuing to develop. Her skin has become soft and smooth, and she's filling out and getting even rounder. She's almost 18 inches long and weighs about 4 3/4 pounds.
37 weeksYour baby is now considered "early term." Babies born now usually do well, but ideally he'll stay in your womb for a couple more weeks to give his brain and lungs time to fully mature.
39 weeksYour baby is now considered full-term and is ready for life outside the womb. The average weight of a newborn is about 7 1/2 pounds, and the average length is about 20 inches.
41 weeksYou've passed your due date and your baby is now considered "late term." (If you're still pregnant at 42 weeks, she's "post term.") Your baby's health may be monitored with tests such as a nonstress test or biophysical profile. To avoid complications, your doctor will probably talk to you about inducing labor in the next week or two.

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Karisa Ding is a health editor and mom in San Franscisco.

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Watch the video: Conception To Birth Fetal Development. Week By Week Fetal Development. Fetal Growth Month By Month (May 2022).

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