A pregnancy test taken at this point can measure hCG, the pregnancy hormone in the mother’s urine, and tell her if she is pregnant. By now, the embryo is completely attached to the lining of the uterus and draws nourishment from its...

The heart begins to beat just 21 days after fertilization or 5 weeks after the mother’s last menstrual period began. The heart, the size of a poppy seed, is the first organ to function. The first signs of brain development are evident, and the...

Just 4 weeks after fertilization, the baby is growing rapidly and measures 1/8 of an inch long. The basic structure of the entire central nervous system (brain and spinal cord) has been formed. The eyes are developing, and the arm and leg buds are...

The baby is now 1/3 of an inch long, and his or her beating heart can be seen on a Doppler ultrasound. The embryo makes its own blood. Depending on the baby’s gender, the testicles or ovaries are beginning to form.

The baby measures ¾ of an inch long and weighs almost 1/8 of an ounce. The developing ears and nose are visible, and there is pigment in the retina. Nipples can now be seen on the chest. The limbs and fingers are growing rapidly, and the bones in...

The baby’s brain is growing rapidly. Each minute, it produces almost 250,000 new neurons! The upper and lower portions of the arms and legs and fingers and toes are seen. By now, the external ear is fully developed. A baby boy begins to produce the...