Each stage of baby development, from fertilization and implantation to the final phases of preparation for delivery, is marked by important milestones and astonishing changes in the baby’s size, structure, and usefulness. These phases reveal the rich and complicated structure of human existence as it takes shape and emerges inside the safe environment of the womb.
Throughout the course of this journey, the baby goes through a succession of developmental stages, with each stage building on the previous weeks’ progress. The baby’s organs, tissues, and bodily systems build and mature gradually, preparing them for life outside the womb.
| Week | Baby Development Stage |
| 1 | Fertilization and implantation |
| 2 | Formation of the placenta and embryo development |
| 3 | Neural tube formation and early brain and spinal cord development |
| 4 | Heart, blood vessel, and limb bud development |
| 5 | Facial feature formation, eye development, and early organ development |
| 6 | Organ development continues, including the lungs, liver, and kidneys. |
| 7 | Hand and foot development, as well as the start of bone formation |
| 8 | Development of distinguishing facial features and eyelids |
| 9 | External genitalia growth, beginnings of muscular development |
| 10 | Development of teeth buds, continuing organ development and maturation |
| 11 | Development of the respiratory, digestive, and sensory systems |
| 12 | Rapid fetal growth and development, creation of the intestines |
| 13 | Vocal cord development and facial feature refinement |
| 14 | Gender may be determined by ultrasound, and bodily structures continue to develop. |
| 15 | Increased mobility and skeletal system development |
| 16 | Nervous system maturation and reflex development |
| 17 | Increased fat storage, sustained muscle and bone growth. |
| 18 | Meconium formation in the intestines |
| 19 | The formation of vernix caseosa, a skin-protective material |
| 20 | Active fetal movements, taste buds development |
| 21 | Rapid brain development, ability to open and close eyelids |
| 22 | Sense of touch and eyebrow development |
| 23 | Continued organ growth and maturation, including the lungs |
| 24 | Development of the respiratory system and surfactant production 25 |
| 25 | Improved lung function and increased chances of survival outside the womb |
| 26 | Development of the nervous system and further brain maturation |
| 27 | Opening of the eyes and start of a regular sleep-wake cycle |
| 28 | Rapid weight gain and continued body system maturation |
| 29 | Fat layer formation for insulation and energy storage |
| 30 | Sucking and swallowing reflexes develop |
| 31 | Continued brain growth and increased sensitivity to stimuli |
| 32 | Immune system development and enhanced antibody synthesis |
| 33 | Additional organ and system growth and development |
| 34 | Toenail and fingernail formation |
| 35 | Lung maturation and readiness for inhaling air |
| 36 | The baby’s last development and placement in preparation for birth |
| 37 | Pregnancy is full-term; baby is termed “early term” |
| 38 | infant’s organs are fully grown and ready for life outside the womb |
| 39 | Baby’s growth and development continue; infant is called “full term” |
| 40 | Waiting for labor and delivery to begin |
Finally, the phases of infant development in the mother’s womb comprise an amazing trip from conception to the end of a full-term pregnancy. The baby goes through an amazing evolution during this time, with each week bringing fresh development and maturation of numerous organs, tissues, and bodily systems.
From the earliest stages of cell division and the production of important structures such as the neural tube and heart to the latter phases of organ development and facial feature refinement, the baby’s development demonstrates the complexity and wonder of human existence.
The baby’s movements grow more evident as the pregnancy proceeds, and its senses begin to develop, allowing them to respond to external stimuli. The baby’s lungs grow, fat stores build up, and his or her body prepares for life outside the womb.
The phases of development serve as a reminder of the complicated processes that occur within the mother’s womb, forming a new life with each passing week. It is crucial to note that these stages are only a guideline; individual pregnancies may differ.
Overall, the phases of newborn development are a monument to the wondrous journey of human reproduction, showing the awe-inspiring nature of creation and the human body’s remarkable power to nourish and maintain new life.