First Month
Fertilization and Implantation:
Formation of blastocyst and implantation into the uterine lining.
Basic structures of the embryo begin to form.
Second Month:
Formation of Major Organs:
Neural tube development leading to the brain and spinal cord formation.
Heart starts to beat, limb buds develop.
Third Month:
Organogenesis:
Development of facial features, limbs elongate.
Organs continue to form and differentiate.
Fourth Month:
Development of Skeletal System:
Ossification of bones.
Fetal movements become noticeable.
Fifth Month:
Development of Senses:
Eyes and ears become more defined.
Lanugo (fine body hair) begins to cover the skin.
Sixth Month:
Lung Development:
Alveoli form in the lungs.
Fetus becomes responsive to external sounds.
Seventh Month:
Rapid Brain Development:
Brain structures mature.
Fetus begins to accumulate subcutaneous fat.
Eighth Month:
Refinement of Organ Function:
Continued growth and maturation of organ systems.
Immune system development.
Ninth Month:
Final Growth and Preparation for Birth:
Fetus moves into the head-down position.
Lungs are fully mature for breathing.
Changes in Placental Membranes:
Formation of Chorion and Amnion:
Chorion and amnion develop early in gestation.
Chorion contributes to the formation of the placenta.
References:
- Moore, K. L., Persaud, T. V. N., & Torchia, M. G. (2015). The Developing Human: Clinically Oriented Embryology (10th ed.). Saunders.
- Sadler, T. W. (2019). Langman’s Medical Embryology (14th ed.). Wolters Kluwer.
- Carlson, B. M. (2014). Human Embryology and Developmental Biology (5th ed.). Elsevier Saunders.
- O’Rahilly, R., & Müller, F. (2010). Developmental Stages in Human Embryos. Carnegie Institution of Washington.