During this time, the fertilized egg travels down the fallopian tube and implants in the uterus. The embryo begins to develop, with the formation of the neural tube, the primitive heart, and the placenta.
The embryo grows rapidly, with the formation of the major organs and systems, such as the brain, lungs, and digestive system. The heartbeat can usually be detected by ultrasound, and the embryo begins to look more like a human.
The embryo is now referred to as a fetus, and begins to develop facial features and limbs. The placenta takes over the role of providing nutrients and oxygen to the fetus, and the fetus begins to move and kick.
The fetus continues to grow and develop, with the formation of bones, teeth, and hair. The sex of the fetus may be visible on ultrasound, and the fetus may begin to suck its thumb.
The fetus grows to about 6 inches in length, and begins to develop a layer of fat under the skin. The mother may feel the fetus moving regularly, and the fetus may begin to hear and respond to sounds outside the womb.
The fetus is now considered viable, meaning that it has a chance of surviving outside the womb with medical assistance. The lungs and other organs continue to mature, and the fetus may begin to open and close its eyes.
The fetus continues to gain weight and develop, with increased brain activity and the ability to recognize voices. The eyes open and close regularly, and the fetus begins to sleep and wake on a regular schedule.
The fetus continues to grow and mature, with increased activity and movements. The bones are fully formed, but still soft and pliable to aid in the birthing process.
The fetus may begin to settle into a head-down position in preparation for birth. The lungs continue to mature, and the fetus may begin to develop a regular sleep-wake cycle.
The fetus is considered full-term, and is ready for delivery. The fetus may have dropped lower into the pelvis, and the mother may experience Braxton-Hicks contractions in preparation for labor. The fetus may weigh between 6-9 pounds and measure 18-22 inches in length at birth.