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.

At 8 weeks, the embryo can respond to touch by reflex. The baby is now about ½ of an inch long. The elbows and fingers can be seen. Some reports show that the embryo can move its trunk and limbs. Lungs begin to develop, taste buds form on the...

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...