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Pregnancy Week by Week

You're pregnant. Congratulations! You'll undoubtedly spend the months ahead wondering how your baby is growing and developing. What does your baby look like? How big is he or she? When will you feel the first kick?
Fetal development typically follows a predictable course. Find out what happens during the first trimester by checking out this weekly calendar of events. Keep in mind that measurements are approximate.

Receiving an ultrasound is the most accurate way to confirm a pregnancy and to determine how far along the pregnancy may be. If you believe you might be pregnant, A Woman’s Friend provides free pregnancy testing and ultrasound services.

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Pregnancy Week by Week

First Trimester
Week 1-3: Getting Ready
Week 4: Implantation
Week 5: The embryonic period begins
Week 6: The neural tube closes
Week 7: Baby's head develops
Week 8: Baby's eyes are visible
Week 9: Baby's toes form
Week 10: Baby's neck begins to develop
Week 11: Baby's genitals develop
Week 12: Baby's fingernails develop
The second trimester: Fetal development
Week 13: Urine forms
Week 14: Baby's sex becomes apparent

Week 15: Baby's skeleton develops bones
Week 16: Baby can make sucking motions
Week 17: Fat accumulates
Week 18: Baby begins to hear
Week 19: Baby's uterus forms
Week 20: The halfway point

Week 21: Baby can swallow
Week 22: Baby's hair becomes visible
Week 23: Fingerprints and footprints form
Week 24: Real hair grows
Week 25: Baby responds to your voice
Week 26: Baby's fingernails develop
Week 27: Second trimester ends

The third trimester: Fetal development
Week 28: Baby's eyes open
Week 29: Baby's bones are fully developed
Week 30: Baby's eyes are wide open
Week 31: Sexual development continues

Week 32: Baby practices breathing
Week 33: Baby detects light
Week 34: Baby's fingernails grow

Week 35: Protective coating thickens
Week 36: Rapid weight gain begins
Week 37: Baby is full term
Week 38: Baby develops a firm grasp
Week 39: Placenta provides antibodies
Week 40: Your due date arrives


First Trimester
Week 1 -3: Getting Ready 
The sperm and egg unite in one of your fallopian tubes to form a one-celled entity called a zygote. If more than one egg is released and fertilized, you may have multiple zygotes.

The zygote has 46 chromosomes — 23 from you and 23 from the father. These chromosomes will help determine your baby's sex, traits such as eye and hair color, and, to some extent, personality and intelligence.
Soon after fertilization, the zygote travels down the fallopian tube toward the uterus. At the same time, it will begin dividing rapidly to form a cluster of cells resembling a tiny raspberry. The inner group of cells will become the embryo. The outer group of cells will become the membranes that nourish and protect it. back to top

Week 4: Implantation
By the time it reaches the uterus, the rapidly dividing ball of cells — now known as a blastocyst — has separated into two sections.

The inner group of cells will become the embryo. The outer group will become the cells that nourish and protect it. On contact, it will burrow into the uterine wall for nourishment. This process is called implantation.
The placenta, which will nourish your baby throughout the pregnancy, also begins to form. back to top

week5Week 5: The embryonic period begins
Fetal development three weeks after conception
The fifth week of pregnancy, or the third week after conception, marks the beginning of the embryonic period. This is when the baby's brain, spinal cord, heart and other organs begin to form.

The embryo is now made of three layers. The top layer — the ectoderm — will give rise to your baby's outermost layer of skin, central and peripheral nervous systems, eyes, inner ear, and many connective tissues.
Your baby's heart and a primitive circulatory system will form in the middle layer of cells — the mesoderm. This layer of cells will also serve as the foundation for your baby's bones, muscles, kidneys and much of the reproductive system.

The inner layer of cells — the endoderm — will become a simple tube lined with mucous membranes. Your baby's lungs, intestines and bladder will develop here.
By the end of this week, your baby is likely about the size of the tip of a pen. back to top

week6Week 6: The neural tube closes
Fetal development four weeks after conception
Growth is rapid this week. Just four weeks after conception, the neural tube along your baby's back is closing and your baby's heart is pumping blood.

Basic facial features will begin to appear, including passageways that will make up the inner ear and arches that will contribute to the jaw. Your baby's body begins to take on a C-shaped curvature. Small buds will soon become arms and legs. back to top

week7Week 7: Baby's head develops
Fetal development five weeks after conception
Seven weeks into your pregnancy, or five weeks after conception, your baby's brain and face are rapidly developing. Tiny nostrils become visible, and the eye lenses begin to form. The arm buds that sprouted last week now take on the shape of paddles.

By the end of this week, your baby might be a little bigger than the top of a pencil eraser. back to top

week8Week 8: Baby's eyes are visible
Fetal development six weeks after conception
Eight weeks into your pregnancy, or six weeks after conception, your baby's arms and legs are growing longer, and fingers have begun to form. The shell-shaped parts of your baby's ears also are forming, and your baby's eyes are visible. The upper lip and nose have formed. The trunk of your baby's body is beginning to straighten.
By the end of this week, your baby might be about 1/2 inch (13 millimeters) long. back to top

week9Week 9: Baby's toes form
Fetal development seven weeks after conception
In the ninth week of pregnancy, or seven weeks after conception, your baby's arms grow, develop bones and bend at the elbows. Toes form, and your baby's eyelids and ears continue developing.

By the end of this week, your baby might be about 3/4 inch (20 millimeters) long. back to top

week10Week 10: Baby's neck begins to develop
Fetal development eight weeks after conception
By the 10th week of pregnancy, or eight weeks after conception, your baby's head has become more round.

The neck begins to develop, and your baby's eyelids begin to close to protect his or her developing eyes. back to top



Week 11: Baby's genitals develop

At the beginning of the 11th week of pregnancy, or the ninth week after conception, your baby's head still makes up about half of its length. However, your baby's body is about to catch up, growing rapidly in the coming weeks.
Your baby is now officially described as a fetus. This week your baby's eyes are widely separated, the eyelids fused and the ears low set. Red blood cells are beginning to form in your baby's liver. By the end of this week, your baby's external genitalia will start developing into a penis or clitoris and labia majora.

By now your baby might measure about 2 inches (50 millimeters) long from crown to rump and weigh almost 1/3 ounce (8 grams). back to top

week12Week 12: Baby's fingernails develop
Fetal development 10 weeks after conception
Twelve weeks into your pregnancy, or 10 weeks after conception, your baby is developing fingernails. Your baby's face now has a human profile.

By now your baby might be about 2 1/2 inches (60 millimeters) long from crown to rump and weigh about 1/2 ounce (14 grams). back to top




The second trimester: Fetal development
Fetal development takes on new meaning in the second trimester. Highlights might include finding out your baby's sex and feeling your baby move.

Find out what happens during the second trimester by checking out this weekly calendar of events. Keep in mind that measurements are approximate.

Week 13: Urine forms
Thirteen weeks into your pregnancy, or 11 weeks after conception, your baby's intestines have returned to his or her abdomen from the umbilical cord — where they've been growing for the past couple of weeks. Your baby is also beginning to form urine and discharge it into the amniotic fluid.

Tissue that will become bone is also developing around your baby's head and within his or her arms and legs. back to top

Week 14: Baby's sex becomes apparent
Fourteen weeks into your pregnancy, or 12 weeks after conception, your baby's arms have almost reached the final relative lengths they'll be at birth and your baby's neck has become more defined. Red blood cells are forming in your baby's spleen.

Your baby's sex will become apparent this week or in the coming weeks. For girls, ovarian follicles begin forming. For boys, the prostate appears.
By now your baby might be almost 3 1/2 inches (90 millimeters) long from crown to rump and weigh about 1 1/2 ounces (40 grams). back to top

Week 15: Baby's skeleton develops bones
Fifteen weeks into your pregnancy, or 13 weeks after conception, your baby is growing rapidly. Your baby's skeleton is developing bones, which will become visible on ultrasound images in a few weeks. Your baby's scalp hair pattern also is forming. back to top

week16Week 16: Baby can make sucking motions
Fetal development 14 weeks after conception
Sixteen weeks into your pregnancy, or 14 weeks after conception, your baby's eyes have begun to face forward and slowly move. The ears are close to reaching their final position. Your baby might be able to make sucking motions with his or her mouth.

Your baby's movements are becoming coordinated and can be detected during ultrasound exams.
By now your baby might be more than 4 1/2 inches (120 millimeters) long from crown to rump. back to top

Week 17: Fat accumulates
Seventeen weeks into your pregnancy, or 15 weeks after conception, fat stores begin to develop under your baby's skin. The fat will provide energy and help keep your baby warm after birth. back to top

Week 18: Baby begins to hear
Eighteen weeks into your pregnancy, or 16 weeks after conception, your baby's ears begin to stand out on the sides of his or her head. Your baby might begin to hear.

By now your baby might be 5 1/2 inches (140 millimeters) long from crown to rump and weigh 7 ounces (200 grams). back to top

Week 19: Baby's uterus forms
Nineteen weeks into your pregnancy, or 17 weeks after conception, a greasy, cheese-like coating called vernix caseosa begins to cover your baby. The vernix caseosa helps protect your baby's delicate skin from abrasions, chapping and hardening that can result from exposure to amniotic fluid.

For girls, the uterus and vagina might begin to form this week. back to top

Week 20: The halfway point
Halfway into your pregnancy, or 18 weeks after conception, you might be able to feel your baby's first movements, also known as quickening. If you've been pregnant before, you might have begun feeling your baby's movements a few weeks ago.

By now your baby might be about 6 1/3 inches (160 millimeters) long from crown to rump. back to top

week21Week 21: Baby can swallow
Fetal development 19 weeks after conception
Twenty-one weeks into your pregnancy, or 19 weeks after conception, your baby is poised to gain more weight. By this week your baby is becoming more active and is able to swallow. back to top

Week 22: Baby's hair becomes visible
Twenty-two weeks into your pregnancy, or 20 weeks after conception, your baby is completely covered with a fine, down-like hair called lanugo. The lanugo helps hold the vernix caseosa on the skin. Your baby's eyebrows might be visible.

By now your baby might be 7 1/2 inches (190 millimeters) long from crown to rump and weigh 1 pound (460 grams). back to top

Week 23: Fingerprints and footprints form
Twenty-three weeks into your pregnancy, or 21 weeks after conception, your baby's skin is wrinkled, more translucent than before and pink to red in color.

This week your baby begins to have rapid eye movements. Your baby's tongue will soon develop taste buds. Fingerprints and footprints are forming. For boys, the testes are descending from the abdomen. For girls, the uterus and ovaries are in place — complete with a lifetime supply of eggs.

With intensive medical care, some babies born this week might be able to survive. back to top

Week 24: Real hair grows
Twenty-four weeks into your pregnancy, or 22 weeks after conception, your baby is regularly sleeping and waking. Real hair is growing on his or her head.

By now your baby might be about 8 inches (210 millimeters) long from crown to rump and weigh more than 1 1/3 pounds (630 grams). back to top

week25Week 25: Baby responds to your voice
Fetal development 23 weeks after conception
Twenty-five weeks into your pregnancy, or 23 weeks after conception, your baby's hands and startle reflex are developing. Your baby might be able to respond to familiar sounds, such as your voice, with movement. back to top




Week 26: Baby's fingernails develop
Twenty-six weeks into your pregnancy, or 24 weeks after conception, your baby has fingernails.
Your baby's lungs are beginning to produce surfactant, the substance that allows the air sacs in the lungs to inflate — and keeps them from collapsing and sticking together when they deflate.

By now your baby might be 9 inches (230 millimeters) long from crown to rump and weigh nearly 2 pounds (820 grams). back to top

Week 27: Second trimester ends
This week marks the end of the second trimester. At 27 weeks, or 25 weeks after conception, your baby's lungs and nervous system are continuing to mature — and he or she has likely been growing like a weed. Your baby's crown-to-rump length might have tripled since the 12-week mark. back to top

The third trimester: Fetal development
Fetal development continues during the third trimester. Your baby will open his or her eyes, gain more weight, and prepare for delivery.

The end of your pregnancy is near! By now, you might be tired of being pregnant — and eager to meet your baby face to face. Your uterus, however, is still a busy place. Understand how fetal development continues as you approach your due date. Here's a weekly calendar of events for the third trimester. Keep in mind that measurements are approximate.

Week 28: Baby's eyes open
Twenty-eight weeks into your pregnancy, or 26 weeks after conception, your baby's eyelids are partially open and eyelashes have formed. Your baby is gaining weight, which is smoothing out many of the wrinkles in his or her skin.

By now your baby might be nearly 10 inches (250 millimeters) long from crown to rump and weigh nearly 2 1/4 pounds (1,000 grams). Otherwise healthy babies born this week have a 90 percent chance of survival without physical or neurological impairment — and the odds improve with each passing week. back to top

week29Week 29: Baby's bones are fully developed
Fetal development 27 weeks after conception
Twenty-nine weeks into your pregnancy, or 27 weeks after conception, your baby's bones are fully developed, but they're still soft and pliable. back to top






Week 30: Baby's eyes are wide open

Thirty weeks into your pregnancy, or 28 weeks after conception, your baby's eyes are wide open a good part of the time. Your baby might have a good head of hair by this week. Red blood cells are now forming in your baby's bone marrow.

By now your baby might be more than 10 1/2 inches (270 millimeters) long from crown to rump and weigh nearly 3 pounds (1,300 grams). back to top


Week 31: Sexual development continues

Thirty-one weeks into your pregnancy, or 29 weeks after conception, your baby's central nervous system has matured to the stage where it can control body temperature. back to top

Week 32: Baby practices breathing
Thirty-two weeks into your pregnancy, or 30 weeks after conception, your baby's toenails are visible.
Although your baby's lungs aren't fully formed, he or she practices breathing. Your baby's body begins absorbing vital minerals, such as iron and calcium from the intestinal tract. The layer of soft, downy hair that has covered your baby's skin for the past few months — known as lanugo — starts to fall off this week.
By now your baby might be 11 inches (280 millimeters) long from crown to rump and weigh 3 3/4 pounds (1,700 grams). back to top


week33Week 33: Baby detects light

Fetal development 31 weeks after conception
Thirty-three weeks into your pregnancy, or 31 weeks after conception, your baby's pupils can constrict, dilate and detect light entering his or her eyes. back to top





Week 34: Baby's fingernails grow
Thirty-four weeks into your pregnancy, or 32 weeks after conception, your baby's fingernails have reached his or her fingertips.

By now your baby might be nearly 12 inches (300 millimeters) long from crown to rump. The pasty white coating that protects your baby's skin — the vernix caseosa — is about to get thicker. back to top

Week 35: Protective coating thickens
Thirty-five weeks into your pregnancy, or 33 weeks after conception, your baby's limbs are becoming chubby. Your baby is gaining weight rapidly — about 1/2 pound (230 grams) a week for the next month. back to top

Week 36: Rapid weight gain begins
Thirty-six weeks into your pregnancy, or 34 weeks after conception, the crowded conditions inside your uterus might make it harder for your baby to give you a punch. However, you'll probably still feel lots of stretches, rolls and wiggles. You might want to check on your baby's movements from time to time (kick count) — especially if you think you've noticed decreased activity. Ask your health care provider how many movements you should detect in a certain number of hours. back to top


Week 37: Baby is full term

Thirty-seven weeks into your pregnancy, or 35 weeks after conception, your baby will be considered full term. Your baby's organs are ready to function on their own.

To prepare for birth, your baby's head might start descending into your pelvis. If your baby isn't head down, your health care provider will talk to you about ways to deal with this issue. back to top

Week 38: Baby develops a firm grasp
Thirty-eight weeks into your pregnancy, or 36 weeks after conception, your baby is developing a firm grasp.
Your baby's toenails have reached the tips of his or her toes. His or her brain might weigh about 14 ounces (400 grams). After birth, your baby's brain will continue to grow. Your baby has mostly shed all of his or her lanugo.

By now your baby might weigh about 6 1/2 pounds (2,900 grams). back to top

Week 39: Placenta provides antibodies
Thirty-nine weeks into your pregnancy, or 37 weeks after conception, your baby's chest is becoming more prominent. For boys, the testes continue to descend into the scrotum.

The placenta continues to supply your baby with antibodies that will help fight infection after birth. If you breast-feed your baby, your milk will provide additional antibodies. back to top

week40Week 40: Your due date arrives
Fetal development 38 weeks after conception
Forty weeks into your pregnancy, or 38 weeks after conception, your baby might be about 18 to 20 inches (450 to 500 millimeters) long and weigh 6 1/2 pounds (2,900 grams) or more. Remember, however, that healthy babies come in different sizes.

Don't be alarmed if your due date comes and goes without incident. It's just as normal to deliver a baby a week or two late — or early — as it is to deliver on your due date. back to top


http://www.mayoclinic.com/health/fetal-development/

 

A Woman's Friend Pregnancy Resource Clinic
961 Live Oak Blvd. • Yuba City, CA 95991

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