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Week 1
The exact moment of conception is virtually impossible to pinpoint due to how sperm interacts with eggs inside the uterus, but doctors use the last day of your last period to estimate the due date of the child. During this time, the uterine lining is thickening to support and fertilize an egg when one is ready to implant. -
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First Trimester
Week 1 through Week 12 -
Week 2
This is the time of ovulation during the week following your last period. The ovary has released one ripened egg (ovum) into the fallopian tubes where it will wait for sperm to fertilize it. The cervix, which is usually plugged with thick, sticky mucus, is now more open and the mucus has thinned to allow for the passage of sperm from the vagina. One sperm will make the 6-8 inch journey to the ovum to fertilize it, which will be conception. -
Week 3
This is the time where the sperm and egg have finally met in the ovum, so it has become a fertilized zygote. 23 chromosomes from the father and 23 chromosomes from the mother are combining to determine the sex, personality, and traits of the child such as eye and hair color. The zygote will move down the fallopian tube and into the uterus for a process known as implantation, where it will receive nourishment from the uterine linng. If you're having multiples, this is when it occurs as well. -
Week 4
The embryo at this time is the size of a grain of rice. It will split into two main parts; the embryo itself and then the placenta- a soft tissue that provides nourishment and oxygen to the embryo throughout pregnancy. A fluid-filled cushion called the amniotic sac develops around the embryo to protect it as it grows. A small yolk sac provides nourishment while the placenta is still developing. -
Week 5
At this point, the baby is a collection of tiny tubes that will all form separate parts of the body. There are buds for arms and legs, the outer ectoderm which forms the CNS, ears, eyes, and connective tissues, the endoderm which forms the lungs, intestines, and bladder, and the middle mesoderm which forms the bones, muscles, kidneys, and reproductive system. The heart will start beating at this time too, but far too softly to hear on the ultrasound. -
Week 6
The fetus is now about the size of a pencil eraser, but it has a tiny heart that now beats at a normal rhythm- about 150 beats per minute! While it still looks like a tadpole, human features like eyes and limbs are beginning to form. The baby is also developing the intestines and lungs that will help it eat and breathe in the coming months. The brain hemispheres are also forming and becoming more developed, so now brainwaves cane be registered and recorded. -
Week 7
The baby has already started forming all of the organs it will need to survive outside the womb including the heart, kidneys, lungs, liver, and intestines. The brain is also becoming more complex with over 100,000 new cells being grown each minute. It's responsible for small jerking movements that the baby will continue making throughout the pregnancy. Tiny buds are starting to form into arms and legs while an umbilical cord connects the baby's systems to yours. -
Week 8
The embryo has graduated to a fetus and now has quadrupled in size. The facial features are becoming more prominent while the body straightens out to appear more human than tadpole. -
Week 9
Eating more milk and dairy products all supply the fetus with the calcium needed to develop strong bones. It weighs 1/8 of an ounce and is about the size of a penny. The head is about 1/2 the size of the full body. The body is developing the reproductive organs, gallbladder, and pancreas which will be vital later in life. The ends of the fingers have also become enlarged with the developing fingerprints. -
Week 10
The tail-like appendage is gone and has been replaced by two tiny legs. The webbing between fingers and toes has also disappeared completely, allowing the baby to look fully human. A well developed facial profile is also present. The bones have begun to harden in the extremities and the kidneys are producing urine. -
Week 11
The fetus has begun to inhale small amounts of amniotic fluid in order to gain lung function for outside the womb. The ears move up from the neck and into place on the sides of the head which is still disproportionally large compared to the rest of the body. The fetus is about the size of a prune, but has developed irises that will allow it to see the world outside the womb. -
Week 12
The end of the first trimester is a time to celebrate because the risk of having a miscarriage has dropped significantly. The fetus has begun to look like a fully formed human as fingers and toes finish developing while the body grows nails and teeth. Tiny movements triggered by the brain allow the fetus to gain muscle mass and reflexes. -
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Second Trimester
Week 13-Week 27 -
Week 13
The body has quickly become more proportional with the head that now only makes up 1/3 of the body. The arms are proportional with the body but the legs still have some growing to do. The eyes have also gained their color, but this can still change well after the child is born. At this point all essential organs and systems have formed and are beginning to function on their own to prepare for life outside the womb. -
Week 14
The fetus is now 4 inches long and weighs 4 1/2 ounces- about the size of a small apple. The body has begun to grow a fine layer of hair called lanugo which will protect the fetus's skin from the temperature and moisture level of the womb. The thumb has already made it's way into the mouth of the fetus, but these sucking and grasping motions develop reflexes that will allow the child to feed once delivered. -
Week 15
The large network of blood vessels that supply nutrients to the body is already forming just beneath the surface of the skin. Here, the fetus is able to gain stronger muscles which it uses on a daily basis to kick, punch, grasp, and make facial expressions. -
Week 16
The fetus has grown to nearly 5 inches long and remains the size of an apple. The bones in the body are becoming harder and more durable, a big difference from the previous cartilage structures. However, these bones will retain some soft spots to aid in the movement through the pelvis and birth canal during labor and delivery. The umbilical cord has also fully matured with two main arteries and one vein suppling nutrients to the fetus- protected by Wharton's Jelly so it moves around the infant. -
Week 17
This week, hair, eyelashes, and eyebrows have begun to grow on the body of the child. Fat is beginning to be deposited underneath the skin and sweat glands are developing, meaning that the fetus is gaining weight more rapidly- a trend that will continue up until birth. The placenta is nearly as large as the fetus as well and will continue to provide nutrients, fats, oxygen, and vitamins to the child while filtering away waste. -
Week 18
The fetus is about 5 1/2 inches long and weighs 5 ounces- equivalent to the size of a cellphone. The bones and nerves surrounding the ears are developed enough to allow the baby to hear, so now is a good time to begin talking to her. The sounds that are naturally produced in the body, such as moving blood and heartbeats, will also trigger responses from the fetus as it grows used to its environment. -
Week 19
The body of the fetus has produced a waxy covering called vernix caseosa that will protect the delicate skin from the amniotic fluid that the fetus sits in until birth. The layer of fat beneath the skin continues to grow thicker to keep the body warm and prepare for life outside the womb. The heart is also growing stronger and beats twice as fast as an adult heart. -
Week 20
The fetus is about 6 1/2 inches long and weighs about 11 ounces so it is about the size fo a banana. The baby continues to put on weight and thus so will you at about 1/2 pound per week. Limbs contnue to move and develop muscles through flexing and kicking while hair, nails, and eyebrows grow in. -
Week 21
The baby is starting to grow even more rapidly because the stomach is able to break down the amniotic fluid and absorb nutrients; however, most nutrients come directly from the placenta still. The intestines now produce meconium, a thick, tarry waste that comes from the amniotic fluid. REM begins to occur and the bone marrow will increase production of red blood cells to increase oxygen supply. -
Week 22
The fetus is now 8 inches long and weighs about 1 pound. The body systems continue to form while hormones and nerves work together to command the systems. The sex organs are also now developed and in place for birth. While the skin is now opaque, it is still wrinkled and covered in vernix until more fat forms under the skin. -
Week 23
The brain now houses billions of brain cells that will control all cognitive and motor functions as well as basic life functions like breathing. Speaking of breathing, the lungs now produce surfactant- a substance that enables the air sacs to inflate and fully expand. This process will prepare the baby for the outside world. -
Week 24
The fetus weighs more than a pounds and is about a foot long. This week marks the period of viability; the fetus can now survive outside of the womb with the aid of medical technology. The wrinkles in the skin are now smoothing out as more fat builds up in the body. The baby will likely move more often and respond to more extrernal stimuli. Also, the inner ear is fully formed and tells the baby if they are upside down. -
Week 25
The fetus now weighs about a pound and a half, which is about the size of a head of broccoli. The heart is now strong enough to hear if you listened from the outside while the diaphragm will begin having spasms causing hiccups. The first bowel movement has also begun to form in the large intestine and will be passed shortly after birth. -
Week 26
The fetus now weighs about 2 pounds, about the size fo a quart of milk that has to be digested each day by the mother to get enough calcium (1,200mg). The eyelids have opened to reveal bluish eyes but this color will likely fade within the first few months of life.It has also developed a distinct sleep-wake pattern where it is either very active or very still. -
Week 27
The sleep schedule of the fetus has finally settled into a pattern but this may be the opposite of the mother's. Hiccuping has beome more freuent as the diaphram continues to spasm, but these won't mkae any sounds because the trachea is filled with fluid and not air. -
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Third Trimester
Week 28- Birth (Week 40) -
Week 28
The fetus now measures about 10 inches long and weighs over two pounds, making it the size of a squash. The fetus will start to move into position for birth with the head facing downward. However, it is not yet a cause for concern if the baby is still breach- facing feet first down the birth canal. -
Week 29
The fetus is growing at an extremely rapid rate and there is less room in the womb. However, the muscles will continue to jerk and move to maintain muscle and bone mass. The brain has developed more wrinkles as more nerve connections are established while the lungs continue to mature. The five senses are also causing more dramatic reactions from the fetus. -
Week 30
The fetus is now 11 inches long and weighs about 3 pounds- about the size of a small roasting chicken. The baby will continue to put on 1/2 pound a week from now until birth. The fat will protect major organs, regulate body temperature, and provide energy. Less movement is also common at this point as the fetus has less room to maneuver around in the womb. -
Week 31
The mother will begin to experience Braxton Hicks contractions that last thirty seconds to two minutes as a preparation for labor in the coming weeks. The baby is also forced into the fetal position because it is too large to stretch out freely in the womb. The reproductive organs are now close to being fully formed too. -
Week 32
The fetus now weighs about four pounds, equivalent to the size of a cantaloupe. Movements in the wombs are much smaller but still occur to maintain muscle and bone mass. The lanugo is also falling off, leaving only eyelashes, eyebrows, and head hair behind. Babies born at this point will go on to live fully functional and healthy lives with the aid of a ventilator while the lungs continue to mature. -
Week 33
The fetus continues to add fat to the growing weight of the body in order to maintain organ function while most bones harden to support the extra weight. However, the skull will remain soft to fit through the birth canal and to accommodate the growing brain. External stimuli will continue to affect the activity level of the fetus as the weeks continue to pass. -
Week 34
The fetus is about a foot long and weighs nearly 5 pounds, roughly the size of a pineapple. Most major organs function on their own and the fetus has reached head-down position for delivery. The vernix caseosa has thickened to protect the fetus during birth but this will easily be washed away during its first bath. -
Week 35
The fetus now weighs in at a whopping 5 1/2 pounds but will continue to put on 1/2 per week up until birth. The baby is settling even lower in the fetus- a movement called "lightening"- and will be ready for delivery soon. If the baby remains in the breech postion the OB-GYN will decide the next best steps to take. -
Week 36
The fetus weighs about 6 pounds, roughly equivalent to the size of a honeydew melon. All substances that used to cover the baby have all but dissolved and been swallowed by the fetus, contributing to the meconium bowel movements. The fat in the fetus now makes up 15% of its total body weight to help improve survival outside of the womb. The sucking muscles in the mouth are also strong enough to breastfeed soon after birth. -
Week 37
The fetus weighs roughly 6 1/2 pounds by this point and is in the "engaged" position in the pelvis in anticipation for labor which can set in at any moment now. The umbilical has begun to pass anitbodies to the baby in preparation for delivery as well. The senses are more heightened and the baby is able to recognize voices and sounds that it has heard throughout pregnancy. -
Week 38
The fetus has now surpassed 6 1/2 pounds but growth has slowed down at this point. However, all organs are fully functional and controlled by the brain. Reflexes are also more active to engage in grabbing and sucking once outside the womb in order to breastfeed. At this point a baby is considered full term, but the pregnancy could last anywhere between 38-42 weeks. -
Week 39
The fetus is now over 7 pounds and is equivalent to carrying a watermelon in the womb. This is close to the birth weight and length, meaning the fetus will probably not grow much more. Braxton Hicks contractions will become more common as you near closer to your due date. The baby is now in it's final position for birth and is ready for delivery. -
Week 40
The average fetus weighs about 7 pounds and measures 20 inches long. Once the baby is delivered, it will be rated on the Apgar scale for factors such as; activity and muscle tone, grimace response, skin appearance, and respiration. Most babies have a score between seven and nine.
