Week 13 of pregnancy
Weeks 13 to 28 is the second trimester of pregnancy.
The ovaries or testes have now developed inside the body. The genitals are forming on the outside of the body. It is still a little too early to see the sex on an ultrasound scan.
Bones are forming and hardening in their arms and legs. Their digestive system had been developing outside their body. By now, it has moved to its permanent location inside the tummy.
At 13 weeks, they weigh around 25g and are about the same size as a peach.
Week 14 of pregnancy
At 14 weeks, they are about 85mm long from head to bottom. Their body is covered in a fine hair called lanugo.
Around now, they begin to swallow little bits of amniotic fluid, which pass into the stomach. The kidneys start to work. They start to make urine (wee). This is released into the amniotic sac (sack of fluids around them) making amniotic fluid.
Week 15 of pregnancy
Around this time, they will start to hear. They may hear muted sounds from the outside world and any noises your digestive system makes. They will also hear the sound of your voice and heart.
Their eyes also start to become sensitive to light. Even though the eyes are closed, they may sense a bright light outside your tummy.
Week 16 of pregnancy
They can now move the muscles in their face. The beginnings of facial expressions appear but cannot yet be controlled.
Their lungs are also developing. They are practicing breathing amniotic fluid in and out.
The nervous system continues to develop. This allows the muscles in the limbs to flex. Around this time, their hands can reach each other. Their hands can form a fist and hold each other when they touch.