BGDA Practical 12 - Third Trimester
Practical 12: Embryo to Fetus | Second Trimester | Third Trimester | Birth | Neonatal | Abnormalities |
Introduction
- Fetal Neural
- Fetal Respiratory
- Fetal Cardiovascular
- survival issues for early delivery
- fetal weight
- fetal origins hypothesis
Week 24+
- Earliest potential survival expected if born
Respiratory
Week 24 to 40 lung histology - terminal sac, end month 6 alveolar cells type 2 appear and begin to secrete surfactant
- saccule - a large thin-walled airspace lined by flattened epithelium present from about 28 weeks gestation to 2 months after birth
Testes Descent
Start of testis descent | End of testis descent |
Fetal Weight
Fetal Birth
Most of the serious illness and mortality is concentrated in the 1 to 2 percent of infants who are born at less than 32 weeks of gestation (week 30) and who weigh less than 1500 g.
Teratogens - Infant Drug Clearance
Teratogen (Greek, teraton = monster) Any agent that causes a structural abnormality following exposure during pregnancy. The overall effect depends on dosage and time of exposure.
The drug clearance data below are only approximate calculated rates for the fetus and infant from NZ Drug Safety in Lactation
Post-conceptual Age (weeks) | Clearance of Drug (percentage of adults) |
24-28 | 5% |
28-34 | 10% |
34-40 | 33% |
40-44 | 50% |
44-68 | 66% |
> 68 | 100% |
Practical 12: Embryo to Fetus | Second Trimester | Third Trimester | Birth | Neonatal | Abnormalities |
Additional Information
The following information is a detailed timeline of third trimester development and content does not form part of the current practical class.
Third Trimester
(Clinical Week 28) Third Trimester
Event | ||
Clinical third trimester | Hearing 3rd Trimester - vibration acoustically of maternal abdominal wall induces startle respone in fetus. | |
Respire Month 7 - respiratory bronchioles proliferate and end in alveolar ducts and sacs | ||
Genital male gonad (testes) descending | ||
Nail Development fingernails reach digit tip | ||
Neural brain cortical sulcation - primary sulci present[1] | ||
Neural brain cortical sulcation - insular, cingular, and occipital secondary sulci present[1] | ||
Nail Development toenails reach digit tip
Lens Development - lens growth and interocular distance plateaus after 36 weeks of gestation[2] | ||
Birth | Clinical Week 40
Heart pressure difference closes foramen ovale leaving a fossa ovalis Thyroid TSH levels increase, thyroxine (T3) and T4 levels increase to 24 h, then 5-7 days postnatal decline to normal levels Adrenal - zona glomerulosa, zona fasiculata present
|
References
BGDA: Lecture 1 | Lecture 2 | Practical 3 | Practical 6 | Practical 12 | Lecture Neural | Practical 14 | Histology Support - Female | Male | Tutorial
Glossary Links
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Cite this page: Hill, M.A. (2024, June 14) Embryology BGDA Practical 12 - Third Trimester. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDA_Practical_12_-_Third_Trimester
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G