4 weeks of gestation: The fetus is only 0.2 cm. The fertilized egg has just completed its implantation, the amniotic cavity has only formed and is very small. Ultrasound does not yet show signs of pregnancy. The brain and spinal cord are beginning to form at this time, and the stomach and intestines are forming. The fetus reaches 0.4 cm and enters the embryonic stage, the amniotic cavity is enlarged, the primitive cardiovascular vessels are present and may be pulsating, and a small fetal sac can be seen on ultrasound, occupying less than 1/4 of the uterine cavity, or a fetal bud may be visible. 6 weeks of gestation: the fetus grows to 0.85 cm, the fetal head, brain vesicles, frontal organs, respiratory, digestive and nervous organs are differentiated, the fetal sac is clearly visible on ultrasound, and the fetal bud and fetal heartbeat are seen. The embryo’s heart can already beat up to 150 times per minute at this time, which is equivalent to twice the adult’s heartbeat. The fetus is 1.33 cm long, the embryo has taken on a human form, all the body segments are differentiated, the limbs are separated, and all systems are further developed; the fetal bud and heartbeat are clearly visible on ultrasound, and the fetal sac occupies about 1/3 of the uterine cavity; the appendix and pancreas have grown, and the pancreas will eventually secrete insulin to aid digestion. The liver is busy making red blood cells and a section of the intestine has begun to protrude into the umbilical cord, which now has clear blood vessels and is beginning to carry oxygen and nutrients back and forth to the fetal body. The fetal head, body and limbs can be distinguished, and the fetal head is larger than the trunk; the ultrasound shows that the fetal sac occupies about 1/2 of the official cavity, the fetal shape and fetal movement are clearly visible, and the yolk sac can be seen. The embryo is now starting to grow with various complex organs. The fetal head is larger than the fetal body and the various parts of the fetus appear more clearly, the head begins to calcify and the placenta starts to develop. Many of the fetal positions have changed. At this time, the sex of the baby cannot be identified by ultrasound, but the baby’s reproductive organs are already growing 10 weeks of gestation: the fetus grows to 2.83 cm, all the fetal organs are formed, the placenta is taking shape, the fetal sac begins to disappear as seen by ultrasound, the lunar bud-shaped placenta is visible, and the fetus is active in the amniotic fluid. The baby’s wrists and ankles are completed and clearly visible. 11 weeks of gestation: The fetus grows to 3.62 cm, all organs of the fetus develop further and the placenta develops; the ultrasound shows that the fetal sac disappears completely and the placenta is clearly visible. Many of the baby’s subtleties begin to appear, such as the appearance of fingernails, and the baby’s fingers and toes can be clearly seen. At the same time, the baby’s bone cells develop faster, the limbs lengthen, and the bones harden with the deposition of calcium salts 12 weeks of pregnancy: the fetus grows to 4.58 cm, the external genitalia develop initially, if there are deformities that can be manifested, and the cranial calcification becomes more perfect. The cranial halo is clear, the biparietal diameter can be measured, obvious malformations can be diagnosed, and thereafter the organs tend to be perfected. The size of the developing fetus is judged by ultrasound during pregnancy is one of the more informative methods. Pregnant women will see some values on the examination report when they have ultrasound, and these values are telling you the size of the developing baby. Now that the baby has taken its first human shape, the baby’s growth rate is getting more and more amazing this week. Week 13: The average fetal biparietal diameter is 2.52 and 0.25, the average abdominal circumference is 6.90 and 0.65, and the femur length is 1.17 and 0.31. The fetal neurons are increasing rapidly, synapses are forming, the fetal conditioned reflexes are strengthening, the fingers are beginning to clasp the palms of the hands, the toes and soles of the feet are bending, and the eyelids are still tightly closed. The baby’s skin is now covered with a fine layer of vellus hair that will disappear after birth. The hair also begins to grow rapidly and the density and color of the hair will change after the baby is born. 15 weeks of gestation: The average biparietal diameter is 3.23 and 0.51, the average abdominal circumference is 9.13 and 1.56, and the femur length is 1.74 and 0.58. The biggest thing that happens to the baby during this week is that he/she starts to hiccup in the womb, which is a precursor to the beginning of the baby’s breathing. At 16 weeks of gestation: the average fetal diameter is 3.62 and 0.58, the average abdominal circumference is 10.32 and 1.92, and the femur length is 2.10 and 0.51. The circulatory system and the urinary tract are also in full working order at this time. The fetus is able to inhale and exhale amniotic fluid continuously during the 16th week. At 17 weeks of gestation, the average biparietal diameter is 3.97 and 0.44, the average abdominal circumference is 11.49 and 1.62, and the femur length is 2.52 and 0.44. The fetus looks like a pear at this time. At 18 weeks of gestation, the average value of fetal biparietal diameter is 4.25 and 0.53, the average value of abdominal circumference is 12.41 and 1.89, and the length of femur is 2.71 and 0.46. The baby’s genitalia are clearly visible. At 19 weeks of gestation, the mean biparietal diameter is 4.52 and 0.53, the mean abdominal circumference is 13.59 and 2.30, and the femur length is 3.03 and 0.50. The most significant change in the baby is the rapid development of the sensory organs according to the region. 20 weeks of gestation: The average value of the fetal biparietal diameter is 4.88 and 0.58, the average value of the abdominal circumference is 14.80 and 1.89, and the femur length is 3.35 and 0.47. The fetal growth is stabilizing. 21 weeks of gestation: The fetus is now about 18 cm long and weighs 300-350 g. At this time the fetus starts to increase its weight significantly. At 22 weeks of gestation, the average fetal biparietal diameter is 5.45 and 0.57, the average abdominal circumference is 16.70 and 2.23, and the femur length is 3.82 and 0.47. At this time, the fetus starts to gain weight significantly and looks like a small baby. The fetus is now about 19 cm long and weighs about 400 g. The fetus’ hearing is basically formed at this time. 24 weeks of gestation: The average fetal biparietal diameter is 6.05 and 0.50, the average abdominal circumference is 18.74 and 2.23, and the femur length is 4.36 and 0.51. The baby is occupying a considerable amount of space in the mother’s womb and is beginning to fill the entire space. 25 weeks of pregnancy: The fetus is now about 30 cm long and weighs about 600 grams. The development of the fetal brain has reached a peak, and the baby’s brain is rapidly proliferating and differentiating at this time with brain cells increasing in size. At 26 weeks of gestation, the average biparietal diameter is 6.68 and 0.61, the average abdominal circumference is 21.62 and 2.30, and the femur length is 4.87 and 0.41. The baby’s subcutaneous fat has begun to appear. 27 weeks of gestation: At 27 weeks, the fetus is now about 38 cm long and weighs about 900 grams. The baby’s eyes are opening and closing at this time, and there is a sleep cycle. The baby will also sometimes put his thumb in his mouth and suck on it. 28 weeks of gestation: The mean biparietal diameter is 7.24 and O.65, the mean abdominal circumference is 22.86 and 2.41, and the femur length is 5.35 and 0.55. The baby occupies almost the entire uterus at this time, and as the space becomes smaller, the fetal movement decreases. 29 weeks of gestation: The baby is now sitting at a height of about 26-27 cm and weighs about 1300 g. The baby’s brain is developing rapidly at this time, and the head is enlarging. The baby’s brain is developing rapidly, the head is also increasing in size, the auditory system is also developing, and the baby’s response to external stimuli is more obvious at this time. At 30 weeks of gestation, the average biparietal diameter is 7.83 and 0.62, the average abdominal circumference is 24.88 and 2.03, and the femur length is 5.77 and 0.47. The brain and nervous system have developed to a certain extent, and the subcutaneous fat continues to grow. At 31 weeks of gestation: the mean biparietal diameter is 8.06 and 0.60, the mean abdominal circumference is 25.78 and 2.32, and the mean femur length is 6.03 and 0.38. The fetus now weighs about 2000 grams. The baby’s subcutaneous fat is more abundant, wrinkles are reduced and it looks more like a baby. 32 weeks of gestation: The average biparietal diameter is 8.17 and 0.65, the average abdominal circumference is 26.20 and 2.33, and the femur length is 6.43 and 0.49. The baby’s genitalia are nearing maturity. At 33 weeks of gestation: the average value of biparietal diameter is 8.50 ¼ 0.47, the average value of abdominal circumference is 27.78 ¼ 2.30, and the average value of femur length is 6.42 ¼ 0.46. The fetus is about 48 cm long and weighs about 2200 g. The fetus’ respiratory and digestive systems are nearing maturity. At 34 weeks of gestation, the average biparietal diameter is 8.61 and 0.63, the average abdominal circumference is 27.99 and 2.55, and the average femur length is 6.62 and 0.43. The fetus is now round and starting to gain weight. The formation of subcutaneous fat will regulate the baby’s body temperature after birth. At the same time, the baby is preparing for delivery, with the head turned down and the head entering the pelvis. At 35 weeks of gestation, the average biparietal diameter is 8.70 and 0.55, the average abdominal circumference is 28.74 and 2.88, and the average femur length is 6.71 and 0.45. The fetus is about 50 cm long and weighs about 2500 g. Both kidneys are fully developed and the liver is fully developed. The two kidneys are fully developed and the liver can metabolize some things on its own. At 36 weeks of gestation: the mean biparietal diameter is 8.81 and 0.57, the mean abdominal circumference is 29.44 and 2.83, and the femur length is 6.95 and 0.47. From the end of this week, the baby will be considered full term. 37 weeks of gestation: The mean biparietal diameter is 9.00 and 0.63, the mean abdominal circumference is 30.14 and 0.52 and the mean femur length is 7.10. The fetus is about 51 cm long and weighs about 3000 g. The baby’s head is now fully in the pelvis. 38 weeks of gestation: The average fetal biparietal diameter is 9.08 and 0.59, the average abdominal circumference is 30.63 and 2.83, and the average femur length is 7.20 and 0.43. The baby’s head is now fully in the pelvis, and the baby’s head is swinging inside the pelvis, protected by the pelvic skeleton around it, so that it will be safe. Week 39: The average fetal biparietal diameter is 9.21 and 0.59, the average abdominal circumference is 31.34 and 3.12, and the femur length is 7.34 and 0.53. All organs of the baby’s body are fully developed at this time, with the lungs being the last organ to mature, and it is usually only a few hours after birth that the lungs establish a normal breathing pattern. The average weight is about 3.3 to 4 kg and the length is about 51 cm. Most of the babies are born in this week.