Normal Fetal Development

Neonatal Disease

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Normal Fetal Development 

Overview:

Normal fetal development progresses through three main stages: the first trimester involves the formation of critical organs and body systems, the second trimester is marked by rapid growth, organ maturation, and the development of functional systems, while the third trimester focuses on further organ maturation and preparation for birth. Key milestones include the development of the central nervous system, cardiovascular system, and lungs, as well as the ability to survive outside the womb with adequate respiratory and metabolic functions by the end of gestation

 1. Lung Development

a. Embryonic Period (Weeks 4-5): During the embryonic period, the lung buds arise from the foregut endoderm around the fourth week of gestation. These buds undergo branching morphogenesis, leading to the formation of the conducting airways. 

b. Pseudoglandular Period (Weeks 5-16): This period is characterized by continued branching of the conducting airways, which form a tree-like structure. The epithelial cells differentiate into various cell types, including ciliated cells, mucous-secreting cells, and non-ciliated Clara cells. Vascularization also begins during this period. 

c. Canalicular Period (Weeks 16-26):

During the canalicular period, the primitive airways further divide into smaller air passages called terminal bronchioles. Respiratory bronchioles, where gas exchange begins, also start to develop. The capillary network around the airways continues to proliferate, improving vascularization. 

d. Terminal Sac Period (Weeks 26-Birth):

In this period, the terminal bronchioles give rise to terminal sacs, which will eventually mature into alveoli. Type I and Type II pneumocytes, responsible for gas exchange and surfactant production, respectively, start to differentiate. Surfactant production begins around week 24-28. 

e. Alveolar Period (Birth to Childhood):

After birth, alveolarization continues. Type II pneumocytes mature and produce surfactant, which reduces surface tension in the alveoli, preventing their collapse during expiration. The number of alveoli increases significantly during the first few years of life, reaching adult levels by around age 8. 

2. Factors Influencing Lung Development:

Several factors influence normal fetal lung development: 

  • Genetics: Genetic factors play a significant role in determining the timing and progression of lung development. 

  • Maternal Factors: Maternal nutrition, exposure to toxins, infections, and maternal stress can impact fetal lung development. 

  • Hormones: Hormones such as glucocorticoids play a crucial role in lung maturation, particularly in the production of surfactant. 

  • Mechanical Forces: Fetal breathing movements and amniotic fluid dynamics influence lung growth and development. 

 

 

3. Babies Development in Weeks 

 

Weeks 23 - 25 

  • Bone marrow begins to make blood cells. 

  • The lower airways of the baby's lungs develop. 

  • Your baby begins to store fat.  

Week 26 

  • Eyebrows and eyelashes are well-formed. 

  • All parts of baby's eyes are developed. 

  • Your baby may startle in response to loud noises. 

  • Footprints and fingerprints are forming. 

  • Air sacs form in baby's lungs, but lungs still aren't ready to work outside the womb.  

Weeks 27 - 30 

  • Baby's brain grows rapidly. 

  • The nervous system is developed enough to control some body functions. 

  • Your baby's eyelids can open and close. 

  • The respiratory system, while immature, produces surfactant. This substance helps the air sacs fill with air.  

Weeks 31 - 34 

  • Your baby grows quickly and gains a lot of fat. 

  • Rhythmic breathing occurs, but baby's lungs are not fully mature. 

  • Baby's bones are fully developed, but are still soft. 

  • Your baby's body begins storing iron, calcium, and phosphorus.   

Weeks 35 - 37 

  • Baby weighs about 5 1/2 pounds. 

  • Your baby keeps gaining weight, but probably won't get much longer. 

  • The skin isn't as wrinkled as fat forms under the skin. 

  • Baby has definite sleeping patterns. 

  • Your little one's heart and blood vessels are complete. 

  • Muscles and bones are fully developed.  

Week 38 - 40 

  • Lanugo is gone except for on the upper arms and shoulders. 

  • Fingernails may extend beyond fingertips. 

  • Small breast buds are present on both sexes. 

  • Head hair is now coarse and thicker. 

  • In your 40th week of pregnancy, it's been 38 weeks since conception, and your baby could be born any day now.