WEEK ONE Week one of a 40 week pregnancy actually starts from the first day of the mother’s last period. Meaning, in the first one-two weeks, the soon-to-be mother, is not actually pregnant. During the first week of pregnancy the uterus sheds it’s lining and the hormones are preparing to release another egg.
WEEK TWO During week two, the sperm and egg unite in the fallopian tube to form a zygote. The zygote will then travel down one of the fallopian tubes toward the uterus. Within the uterus, the zygote will divide to form a cluster of cells. The inner group of cells in the cluster is the embryo. The outer layer of cells acts as membranes that nourish and protect the embryo.
WEEK THREE The developing embryo, also called a blastocyst, is looking for a spot to implant in the uterus. When the embryo reaches the uterus, it will burrow into the uterine wall for nourishment. The placenta also starts to form at this time. Amniotic fluid also begins to collect at this time around the ball of cells in the cavity that will become the amniotic sac.
WEEK FOUR The fourth week marks the beginning of the embryonic period. During this week, the formation of the brain, digestive system, spinal cord, heart and other organs begins. At the end of this week the embryo is approx. 10,000 times larger the size at conception.
WEEK FIVE During this week, the heart begins to beat. The brain has developed into 5 areas and cranial nerves are visible.Arm and leg buds are also visible, as well as the formation of the eyes, lips, nose and umbilical cord. At this point, the spinal cord is growing more rapidly than the rest of the body, and gives for a tail-like appearance, which eventually disappears as the embryo grows. During this week, it is the first time the blood vessels complete a circuit, meaning the circulatory system is the first functional organ system.
WEEK SIX The formation of the lungs have begun at this time and further development of the brain. Arms and legs have lengthened with foot and hand areas distinguishable. The intestines begin to grow outside the body, within the umbilical cord, nostrils start to form as well as the pancreas. The embryo is about 1/8 of an inch long at this point.
WEEK SEVEN Embryo has developed it’s own blood type and elbows and toes are visible. Also, all essential organs have at least begun to form. The teeth have also started to develop under the gums.
WEEK EIGHT During this week, rotation of intestines occurs, facial features continue to develop, and eyelids are more developed. The external features of the ear also begin to take their final shape. The tongue starts to form, the intestines move into the abdomen from the umbilical cord and the fingers and toes are still partially webbed. At the end of this week, the embryo is about ½ an inch in length. This week is also the end of the embryonic period.
WEEK NINE Movement takes place this week, although the mother is not able to feel it yet. The embryonic “tail” has also disappeared by this week. Most joints are formed by now and finger prints are evident in the skin. The head also consists of half of the body’s size and mass. The internal reproductive organs, such as testes or ovaries, start to develop. The eyelids have also been fused shut, and won’t reopen until the 26 th -28 th week. Rapid growth will occur after this week due to the fact that the physical features have, or soon will be, developed.
WEEK TEN The embryo is now called a fetus. It is now in the fetal period. Facial features, limbs, hands feet fingers and toes become apparent. The fetus’s brain rapidly produces neurons, about 250,000 a minute. If the fetus is a boy, the fetus will start producing testosterone this week. The fetus is about an inch in length. The fetus’s head is about half of it’s body length at this point, but the rest of it’s body will catch up soon and will become proportionate to it’s brain.
WEEK ELEVEN During this week, fingers and toes have separated and hair and nails have started to develop. All organ systems should be functioning at this point and the developing bones should start to harden. The fetus should also be making lots of movement; kicking and stretching. Genitals begin to take the characteristics of the proper gender. The fetus should also be about 1 ½ inches in length by this point.
WEEK TWELVE During this week, the fetus’s vocal cords begin to form. Their eyes begin to move closer together, ears shift to the sides of their head, and their intestines move further into their body. The liver begins to create bile, the kidney begins to secrete urine in the bladder and pancreas begins to produce insulin. Now, the fetus is about 2 inches in length and weighs about ½ an ounce.
WEEK THIRTEEN Fetus should be approx. 3 inches in length and nearly weighs an ounce. During this week, the fetus starts making inhaling and exhaling movements. The fetus’s neck is getting longer. The placenta is providing nourishment and removing waste from the fetus. The fetus’s hands are becoming more functional, they would either start sucking their thumb at this point or start playing with their fist.
WEEK FOURTEEN During this week, the thyroid gland has matured and is now producing hormones. In boys, prostate gland develops and in girls, the ovaries move from the abdomen to the pelvis. The fetus becomes covered in fine hair called lanugo, which protects the fetus’s skin from the water surrounding it. Eyebrows also start to come in and hair on top of the fetus’s head starts to sprout. At this point, the fetus is about 3 ½ inches in length and approx. weighs 1 ½ ounces.
WEEK FIFTEEN The fetus is about 4 inches in length and weighs about 2 ½ ounces. Legs are now longer than the arms, nails are fully developed and all joints and limbs are able to move. With the help of an ultrasound, the genitals of the fetus may now be apparent enough to determine of which gender it is. The fetus has also started developing taste buds. Sweat glands also start to appear on the fetus.
WEEK SIXTEEN The fetus is about 4 ½ inches in length now, and weighs approx. 3 ½ ounces. Fat is starting to develop underneath the fetus’s skin acting as insulation. The fetus’s heart is pumping about 6 gallons of blood per day. Also, in girls millions of eggs are forming in the ovaries. The fetus has now developed reflexes such as sucking, swallowing, hiccupping and blinking. The fetus has learned to breathe ! Though, it is not breathing air at the moment, but amniotic fluid.
WEEK SEVENTEEN The fetus has more human-like posture, with head erect and away from chest and the body and limbs more proportionate to the head. The umbilical cord is also being stronger and thicker. Merconium starts to develop; a black gooey substance which is will become the fetus’s first feces. The fetus’s skeleton, which is still rubbery cartilage at this point, is starting to harden into bone. The fetus is a bit over 5 inches in length and approx. weighs 5 ounces.
WEEK EIGHTEEN The fetus is about 6 inches in length and nearly weighs 7 ounces. If the fetus is a girl, her uterus and fallopian tubes are formed and in place. If the fetus is a boy, his genitals are visible. Ventricles and chambers within the fetus’s heart are visible through an ultrasound. The ears have shifted to it’s proper location, and the nerves from the brain have “hooked up” to the ears, giving the fetus the ability to hear now. Pads are also developing on the fingers and toes.
WEEK NINTEEN During this week, the fetus has recognizable sleep patterns, those of a newborn. Myelin, a fatty substance, starts to insulate the nerves so impulses can flow smoothly. Vernix, a pasty white coating,on top of Lanugo, helps protect the fetus from the water surrounding it. Sensory development reaches a peak. The brain has developed regions for the fetus’s senses – taste, vision, hearing, touch and smell.
WEEK TWENTY HALF WAY THERE ! The fetus’s heart is growing stronger, their legs are reaching their relative size and immune cells are being transferred from the mother to the baby. The rapid growth is starting to slow down. With the help of vernix, the fetus’s skin is thickening and developing layers. “Quickening” usually occurs during this week; the mother being able to feel the fetus moving. The fetus is about 6 ½ inches in length and weighs approx. 9 –11 ounces.
WEEK TWENTY-ONE White blood cells are starting to produce. The fetus’s skin has changed from translucent to opaque, and the it’s tongue has fully formed. If the fetus is a girl, the womb and vagina are formed. The fetus starts to swallow more, it takes in amniotic fluid that helps with their digestive system. From the amniotic fluid, the fetus receives sugar. The fetus is about 11 inches in length and weighs approx. 13 ounces.
WEEK TWENTY-TWO At this point, fetuses will be able to hear you if you sing or read to them. Eyelids and eyebrows are fully formed and fingernails now cover the fetus’s fingertips. If the fetus is a male, his testes begin to descend to the scrotum. The fetus will be approx. weigh a pound at this point.
WEEK TWENTY-THREE The fetus’s eyes are formed, but the iris still lacks pigment. If the fetus were to be born now, there would be a a slim chance of survival. Blood vessels within the lungs of the fetus develop to help prepare the baby for breathing once the fetus is born.
WEEK TWENTY-FOUR The fetus will gain close to 6 ounces this week in muscle, bone and organs. This week the fetus is considered to be viable. The fetus is about 12 inches in length and close to 1 ½ lbs. Footprints start to develop, as well as aveoli (air sacs) in the lungs. The fetus is beginning to go through rapid brain development at this time.
WEEK TWENTY-FIVE The spine begins to form joints, ligaments and rings which serves protection for the fetus’s spinal cord. The fetus’s nostrils begin to open. Optic nerves are functioning; if a light was placed on the mother’s stomach, the fetus would turn it’s head away from the light. Bones are continuing to become harder and stronger.
WEEK TWENTY-SIX Lungs begin to secrete surfactant, to help prevent the fetus’s lungs from sticking together after the fetus is born. The fetus’s eyes may start to open and blink. Veins are visible through the fetus’s skin. The fetus may be able to cry. The fetus will be approx. 14 inches in length and approx. weigh 2 lbs.
WEEK TWENTY-SEVEN The fetus’s response to sound continues to grow. The fetus’s lungs, liver, brain and immune system are maturing. It is believed fetuses start to have dreams around this week. Eyelids become open more frequently; the fetus can distinguish between light and dark. The fetus will weigh around 2 lbs. at this point and will approx. be 14 ½ inches in length.
WEEK TWENTY-EIGHT The fetus is becoming more filled out due to the increase in muscle tissue and bone. In girls, the clitoris is relatively prominent because it's not yet covered by the still-small labia. The fetus will now weigh just over 2 lbs. and be almost 15 inches in length.
WEEK TWENTY-NINE Fat is being developed underneath the fetus’s skin. The fetus’s brain is now able to control breathing and body temperature. The fetus’s eyes can move in their sockets. Also, it is sensitive to changes; light, sound, taste and smell. The fetus is starting to store iron, calcium and phosphorus. The fetus’s movements might be a bit more aggressive and frequent.
WEEK THIRTY Early lanugo is starting to disappear. Toenails are almost completely formed. Bone marrow is now in charge of red cell production. The fetus is able to follow a light source around. The fetus would approx. weigh around 3 lbs. And would be about 15 ½ inches in length.
WEEK THIRTY-ONE The fetus goes through another rapid brain growth where billions of nerve cells are formed. Lungs are the only major organ that isn’t completely developed. The fetus would need assistance for breathing if they were born now. Arms, legs and body are filling out and are now finally proportionate to the fetus’s head.
WEEK THIRTY-TWO The fetus is not moving as much now due to the lack of room inside the uterus. Toenails are completely formed. Lanugo is starting to shed and fall off of the baby. The fetus weighs just under 4 lbs. and is nearly 17 inches in length.
WEEK THIRTY-THREE Fetus’s head has increased in size by approx. 3/8 th of an inch due to the rapid brain development. Neurons and synapses are also increasing in huge numbers. Fetus’s skull is developed, but still pliable and not completely joined, this helps ease the fetus out of the narrow birth canal. The fetus’s skin is becoming less red and wrinkled.
WEEK THIRTY-FOUR The fetus is turning into the head-down position in preparation for birth. Hearing is fully developed. The fetus will continue to fill out and become rounder due to fat layers developing underneath the fetus’s skin. The fetus urinates approx. a pint a day. The fetus weighs nearly 5 lbs. and is approx 18 inches in length.
WEEK THIRTY-FIVE Kidneys have fully developed and liver can now produce some waste products. The fetus will survive if born now. Organs systems are all present, and are just going through some finishing touches before the fetus’s birth. Most of the physical development is complete, from now until birth the fetus will put on weight.
WEEK THIRTY-SIX Due to the recent fat deposit, fat is dimpling the fetus’s elbows, knees and is creating creases in the fetus’s neck and wrists. The fetus continues to drop further into the pelvis of the mother. The lanugo and vernix has almost been completely shed off of the fetus. The baby should weigh around 6 lbs. and be about 19 inches in length.
WEEK THIRTY-SEVEN The fetus is now cradled in the pelvic cavity of the mother and is protected by her pelvic bones. At this time, many fetuses have a full head of hair, where others do not. The fetus continues to become rounder as more fat layers are being developed. The fetus is now considered full term, meaning the fetus will be able to survive if born now.
WEEK THIRTY-EIGHT All organ systems are still developing and fine tuning. More meconium is developing. The fetus is nearly 7 lbs. and is about 20 inches in length.
WEEK THIRTY-NINE Outer layers of the fetus’s skin if shedding off while new skin developing underneath. Placenta provides fetus with antibodies to help it to survive during the first six months after birth. Some fetuses are already born by this week.
WEEK FORTY BABY DUE DATE ! If fetus is not born during this week, it is normal. If the baby is born, there might still be some vernix present on the baby, the baby will be approx. 15% fat and the baby’s skull bones would still be partially separated. The average newborn is approx. a bit over 7 lbs. and 20 inches in length.