Talk:2010 BGD Practical - Fetal Development

The fetal period (9-36 weeks) is about continued differentiation of organs and tissues, most importantly this period is about growth both in size and weight. The tables showing second and third trimester on this page are to indicate some selected systems developmental changes, you are not required to know detailed timings or events.

Topics

Second Trimester

• Early fetal - week 10, week 12
• placental changes and fetal membrane changes
• length changes
• clinical diagnosis (ultrasound), genetic
• survival issues for early delivery

Third Trimester

• fetal weight
• fetal origins hypothesis
• parturition
• neonatal issues

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Embryonic Week 8

Fetal Week 10

Week 10, 40 mm, female fetus, early fetal stage of development

Fetal Week 12

Second Trimester

Third Trimester

Introduction

This page shows some key events of human development during the fetal period (weeks 9 to 37) following fertilization. Clinically this period is generally described as the Second Trimester and Third Trimester. Many of the critical measurements of growth are now carried out by ultrasound and this period ends at birth.

Links: Lecture - Fetal Development | original page

<Flowplayer height="300" width="285" autoplay="true">fetal growth.flv</Flowplayer>

Animation shows the changing proportions of the fetus, not the growth in size.

Many different systems formed in the embryonic period (organogenesis) grow and differentiate further during the fetal period and do so at different times. For example, the brain continues to grow and develop extensively during this period (and postnatally), the respiratory system differentiates (and completes only just before birth), the urogenital system further differentiates between male/female, endocrine and gastrointestinal tract begins to function.

The Embryonic period involved transient structures to establish body and placental tissues, folding and form.

The long Fetal period (4x the embryonic period) is a time of extensive growth in size and mass as well as ongoing differentiation of organ systems established in the embryonic period.

Also consider the systems (respiratory, cardiac, neural) that will still not have their final organization and function determined until after birth.

Reading

• Human Embryology (3rd ed.) Larson Ch15: Fetal development and the Fetus as Patient p481-499
• Color Atlas of Clinical Embryology (2nd ed.) Moore, Persaud and Shiota Ch3: 9th to 38th weeks of human development p50-68

Second Trimester

Fetus - second trimester (ultrasound)

• Second Trimester
• Week 12 - CRL 85 mm, femur length 15 mm, biparietal diameter 25 mm.

Third Trimester

Fetus - third trimester (historic image)

• Third Trimester
• Vibration acoustically of maternal abdominal wall induces startle respone in fetus.
• Month 7 - respiratory bronchioles proliferate and end in alveolar ducts and sacs.
• Week 37 to 38 Birth.

References

Reviews

• Fetal assessment during pregnancy. Farley D, Dudley DJ. Pediatr Clin North Am. 2009 Jun;56(3):489-504, Table of Contents. Review. PMID: 19501688
• Regimens of fetal surveillance for impaired fetal growth. Grivell RM, Wong L, Bhatia V. Cochrane Database Syst Rev. 2009 Jan 21;(1):CD007113. Review. PMID: 19160321

Search PubMed

Search Pubmed: fetal+development | Second Trimester | Third Trimester