fetal develop

Fetal Development and Embryology

  • Embryology

    • Developmental process that transforms a fertilized egg into a fetus prepared for birth.

    • Involves various stages of growth and changes in structure.

The Placenta

  • Function: Critical for fetal survival, responsible for:

    • Development

    • Nutrition

    • Waste deposition

    • Respiration.

Fetal Growth and Development

  • Definition: Fetal growth is described as "an increase in size, which occurs by cell multiplication, increase in cell size and deposition of extracellular material" (Wolpert et al., 2015).

  • Growth Rate:

    • Average fetal growth rate is approximately 1.5 mm per day.

Gestational Age

  • Determined from the last menstrual period (LMP).

  • Duration: 40 weeks after LMP.

  • Ultrasound scan can estimate the date of fertilization, typically dated as 38 weeks post-fertilization.

  • Fetal Growth Measurement: Crown-to-rump length.

  • Definitions of Term:

    • Preterm: 24+0 to 36+6 weeks.

    • Full term: 37+0 to 40+6 weeks.

    • Post term: More than 41 weeks.

Cellular Processes in Fetal Growth

  • Cell Growth Mechanisms:

    • Growth occurs via:

    • Cell Proliferation (Hyperplasia): Increase in cell numbers.

    • Cell Enlargement (Hypertrophy): Increase in cell size.

    • Extracellular Material Deposition: Formation of the cellular matrix and structures surrounding cells.

  • Apoptosis:

    • Definition: Programmed cell death, essential for regulating overall growth rate.

    • Role in development:

    • Sculpting the organism by eliminating unwanted structures.

    • Example: Separation of fingers during development occurs via apoptosis.

Growth Patterns in Pregnancy

  • Early Pregnancy: Rapid growth predominantly through hyperplasia.

  • Post 24 Weeks: Growth slows but remains consistent, transitioning to hypertrophy after 34 weeks.

Control of Cell Growth

  • Key Factors:

    • Placental Growth Factors and Proteins: Crucial for regulating fetal cell growth and proliferation.

    • Insulin-like Growth Factor (IGF):

    • Enhances amino acid and glucose uptake while inhibiting protein breakdown.

    • IGF1: Major direct endocrine stimulus.

    • IGF2: Indirect effects; promotes placental growth and transportation mechanisms.

Genomic Imprinting

  • Definition: Fetal growth might be influenced by competition between maternal and paternal genes.

  • IGF2:

    • Inherited from the father, functions as a growth factor enhancing fetal development.

  • Maternal Influence:

    • Maternal genes can limit fetal growth; maternal height is correlated with uterine capacity.

    • Smaller women tend to have smaller babies.

Fetal Weight

  • Weight Gain:

    • Fetus typically gains approximately 25g daily from 32 to 40 weeks.

  • Average Birth Weight: approximately 3400g.

  • Weight Classifications:

    • Large for Gestational Age (LGA): over 4000g, risk of shoulder dystocia.

    • Small for Gestational Age (SGA): under 2500g, risk of perinatal morbidity and mortality.

Factors Affecting Fetal Growth

  • Maternal Factors:

    • Height, weight, ethnic origin, parity, diabetes, hypertension, lifestyle factors (diet, exercise), infections, multiple pregnancies.

  • Fetal Factors:

    • Male fetuses tend to be heavier than females.

    • Ovarian capacity to synthesize steroid hormones is limited; testosterone has anabolic effects.

Maternal Size and Its Impact

  • The size of the mother is a crucial determinant of fetal weight:

    • Smaller maternal size may limit fetal growth due to restricted space.

    • Maternal height linked with socioeconomic factors, genetics, and potential malnutrition.

The Uterine Environment

  • Provides optimal conditions for organ system development:

    • Uterine blood vessels respond to estrogen and progesterone by relaxing and dilating, enhancing nutrient flow to the fetus.

  • Amniotic Fluid:

    • Creates space for the developing fetus, cushioning against external pressure, allowing normal lung development, and supporting growth.

    • Rich auditory stimuli are present, including rhythmic sounds of blood flow.

    • Maternal movements provide kinaesthetic and vestibular stimulation that aid neurodevelopment.

Size Changes During Pregnancy

  • Fundus Measurements:

    • At 12 weeks: just above the pubic bone.

    • At 36-38 weeks: right up under the sternum.

    • At 40 weeks: fundus drops below the 38-week level as the presenting part descends into the pelvis.

Terminology in Midwifery

  • SGA: Small for Gestational Age

  • FGR: Fetal Growth Restriction

  • LGA: Large for Gestational Age

The Fetoplacental Unit (Tucker Blackburn, 2013)

  • The placenta occupies approximately one-third of the uterine surface area.

    • Sufficient placental function is crucial for adequate hCG production to maintain early pregnancy.

    • Fetal membranes exhibit a high regenerative capacity for cortisol through the action of 11β-hydroxysteroid dehydrogenase 1.

Maternal Nutrition

  • Pre-Conceptional Nutrition:

    • Sets the foundation for fetal growth; good nutrition optimizes nutrient availability, especially important during late gestation.

  • Placental Dysfunction: Can restrict nutrient transfer to the fetus.

Maternal Behavior

  • Harmful behaviors affecting fetal health include:

    • Smoking: Induces vasoconstriction through nicotine.

    • Alcohol Misuse: Linked to fetal alcohol syndrome; no alcohol is recommended during pregnancy.

    • Drug Misuse: Can lead to adverse developmental outcomes.

Measuring Fetal Growth

  • Observational methods include:

    • Visual assessments.

    • Symphysis fundal height measurements.

Conclusion

  • Complexity of Fetal Growth:

    • Influenced by genetic and environmental factors, including genomic imprinting and cellular growth regulation.

    • The uterine environment is optimal for the fetoplacental unit, but various placental, fetal, and maternal factors can affect growth and development.

  • Importance of Monitoring: Fetal growth is a critical indicator of fetal health, making regular monitoring essential.

  • Understanding A&P of Fetal Development: Knowledge is fundamental to assessing fetal growth effectively.

Organogenesis

  • Definition: The formation of organs begins in the first trimester of pregnancy.