Abnormal Development - Fetal Growth Restriction

Introduction

Relative fetal sizes

This page shows some key events of human development during the fetal period (weeks 9 to 37) following fertilization. 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. 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.

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

Historic Embryology
1940 Fetus Physiology
Carnegie Fetal: 95 \| 96 \| 142 \| 145 \| 184 \| 211 \| 217 \| 300 \| 362 \| 448 \| 449 \| 538 \| 590 \| 607 \| 625 \| 662 \| 693 \| 847 \| 858 \| 922 \| 928 \| 948 \| 972 \| 1318 \| 1388 \| 1455 \| 1591 \| 1597b \| 1656 \| 1686 \| 2250a \| 2250b \| 3990 \| 5652 \| 6581 \| 7218

Some Recent Findings

Fetus (week 10)

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Reading

Human Embryology (3rd ed.) Larson Chapter 15: Fetal development and the Fetus as Patient p481-499
The Developing Human: Clinically Oriented Embryology (8th ed.) Moore and Persaud Chapter 6: The Fetal Period: Ninth Week to Birth
Color Atlas of Clinical Embryology (2nd ed.) Moore, Persaud and Shiota Chapter 3: 9th to 38th weeks of human development p50-68

‎‎Fetal Development

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Fetal length and weight change

Second Trimester

Fetus - second trimester
(ultrasound)

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

Begin by working through the features present in the early 10 week female fetus. Then look in detail at the head development in a 12 week fetus.

**10 Week Fetus** *head images*

Then look in detail at the head development in a 12 week fetus showing both forms of ossification in the skull.

**12 Week Fetus** *head images*

Fetal Head Growth

Second and third trimesters
Second trimester

Third Trimester

Fetus - third trimester
(historic image)

Third trimester Crown-Rump Length

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.

Links: Third Trimester