| 1 | Fertilization occurs. The fertilized egg implants in the uterus. |
| 2 | The fertilized egg begins to divide and form a blastocyst. |
| 3 | The blastocyst implants deeper into the uterine lining. |
| 4 | The embryo begins to develop major organs such as the heart, brain, and spinal cord. |
| 5 | Limb buds start to form, and the heart begins to beat. |
| 6 | Facial features begin to develop, and the embryo starts to resemble a human. |
| 7 | Organs continue to develop, and the embryo grows rapidly. |
| 8 | The embryo is now called a fetus. Arms and legs are more defined. |
| 9 | Fingers and toes start to form. |
| 10 | Facial features become more distinct. |
| 11 | The fetus can make spontaneous movements. |
| 12 | The fetus is now fully formed and can be seen on an ultrasound. |
| 13 | The fetus begins to produce urine, and its vocal cords start to develop. |
| 14 | Gender can sometimes be determined via ultrasound. |
| 15 | The fetus can respond to external stimuli, such as sound. |
| 16 | The fetus grows rapidly, and the mother may start to feel movements. |
| 17 | The fetus's skeleton begins to harden, and it can suck its thumb. |
| 18 | The mother may start to feel more pronounced movements. |
| 19 | Vernix, a protective coating, forms on the fetus's skin. |
| 20 | The halfway point of the pregnancy. Organs continue to mature. |
| 21 | Eyebrows and eyelids develop. |
| 22 | The fetus can perceive light, and its lungs continue to develop. |
| 23 | Rapid brain growth occurs. |
| 24 | The fetus's hearing continues to improve. |
| 25 | The fetus's skin becomes less transparent. |
| 26 | Lung development continues, and the fetus may begin to experience REM sleep. |
| 27 | The fetus's lungs are capable of breathing air, although they are not fully mature. |
| 28 | The fetus's eyes open, and it can blink. |
| 29 | The fetus's nervous system continues to develop. |
| 30 | The fetus's bones continue to harden. |
| 31 | The fetus's movements may be felt more intensely by the mother. |
| 32 | The fetus's skin becomes smoother as fat deposits increase. |
| 33 | The fetus's bones are fully developed, but still soft. |
| 34 | The fetus continues to gain weight rapidly. |
| 35 | The fetus's immune system begins to develop. |
| 36 | The fetus moves into the head-down position in preparation for birth. |
| 37 | The fetus's lungs are fully developed and ready for breathing. |
| 38 | The fetus continues to grow, although at a slower rate. |
| 39 | The fetus may drop lower into the pelvis in preparation for birth. |
| 40 | Full term. The baby is ready for birth. |