Fetal development, second trimester

| In the second trimester of pregnancy, the embryo already has a human shape and is called a fetus. During the following weeks it will begin to grow and mature

The fetus has already organ formation completed and what it's basically going to do is grow and mature.

• At 14 weeks the fetus is about 9 cm and weighs about 25 g. The neck begins to elongate and the head continues to be flexed towards the thorax. The eyes are still closed and the skin is very thin and the blood vessels can be seen through.
• In the week 15 measures between 9 and 10 cm and weighs about 50g. The ultrasound measurements used from this moment on are the biparietal diameter (the measurement from one side of the head to the other), the abdominal circumference and the length of the femur. The fetus is covered with a very fine hair called lanugo. The eyes are approaching their final position and the ears begin to have creases.
• In the week 16 it already measures between 10 and 11 cm. The legs are already longer than the arms and knees, ankles, elbows and wrists can be differentiated. He begins to kick in a coordinated way even though they are not yet noticeable.
• In the week 17 It is already about 12 cm and weighs about 100g. It begins to look more like a newborn. Fat under the skin builds up, which is very important for maintaining body temperature. Its most frequent position is with the hands in the face and the feet crossed under the exit of the umbilical cord.
• In the week 18 It measures between 13 and 14 cm. The ossification nuclei of the extremities are formed, cartilage until the moment that they are transformed into bone tissue.
• In the week 19 the fetus measures between 14 and 16 cm. The growth rate is a bit slower. It continues to develop in nervous system and spinal cord. Cheesy vermix forms, a fat that coats the body and protects it from abrasions, cracks, and hardening from continuous exposure to amniotic fluid.
• At 20 weeks the proportions of the extremities with respect to the body are already the final ones. If it is a girl, the uterus is formed and the canalization of the vagina begins. The growth of the fetus is already measured by parts in the ultrasound: the head, the abdomen and the femur.
• At 21 weeks is already able to swallow amniotic fluid that will pass to the stomach and the small and large intestines.
• At 22 weeks the eyelids, eyebrows and eyelashes are distinguished. The testicles begin their descent from the abdomen into the scrotum. Its approximate weight is 475g.
• At 23 weeks rapid eye movements begin. The skin is wrinkled and very thin.
• At 24 weeks it is considered a viable fetus despite having a low survival rate and a high complication rate. He begins to hear and has startle and blink reactions to vibroacoustic stimulation.
• At 25 weeks the convolutions or folds of the outer aspect of the brain begin to develop.
• At 26 weeks they have great activity and movement and react to light so the optic nerve already works. The senses are already developed. Surfactant begins to form in the lungs to allow it to function properly postpartum. The weight of the fetus is about 900g and the size up to the coccyx about 23 cm.