Week 6 of pregnancy is considered early pregnancy and is about halfway through the first trimester. Some women find out they are pregnant around this time. Babies at this stage can be measured with an ultrasound, although many details may be difficult to see. Many babies develop at different speeds, however most babies at six weeks' gestation will have several size, organ and body features in common.
At 6 weeks old, an unborn baby is about a quarter of an inch long. His size can be compared to a lentil bean, nail head or half of a baby pea. At this point, he also weighs 0.001 ounce. Unborn babies are typically measured through ultrasound from the crown of the head to the rump, since when arms and legs eventually develop, they can be scrunched or bent in varying directions, making them difficult to measure.
An unborn baby will have an over-sized head at six weeks along. Her nose, mouth and eyes are beginning to take shape and are only dark spots on her face at this age. Her ears are beginning to form and are small depressions on either side of her head. Her jaw, cheeks and chin are also becoming more prominent, although she is still so small that it will be difficult to see any features in an ultrasound.
Although his body is still scrunched and curled up, an unborn baby has arms and legs. They are only tiny buds, but will soon grow in length. He has fingers and toes with webbing in between, and his skin is still forming, although it will be covered in a protective layer -- vernix -- until shortly before birth. His muscles and bones are also beginning to form and will be soft until birth.
Blood is beginning to flow through her body, and due to her developing central nervous system she is able to respond to touch. Her heart is beating 100 to 160 times each minute, which is almost twice as fast as the mother's heartbeat. Her heartbeat may also be visible on an ultrasound screen as a small flicker, but will not be audible for a few more weeks. Buds of tissue are present where her lungs will be, and her brain, pituitary gland, kidneys and liver are developing as well.
At 6 weeks old, an unborn baby is floating in the amniotic sac. The umbilical cord that connects him to his mother is beginning to lengthen, allowing for him to grow and begin moving more in a few weeks. He is also getting all of his nutrition from the yolk sac, which is located inside the gestational sac and is usually visible with an ultrasound by week 6.