9.2 Fetal Development Flashcards
What are the 3 main periods of pregnancy?
Pre- embryonic (0 to 2 weeks)
Embryonic (3 to 8 weeks)
Fetal (9 to 38 weeks)
What happens during the fetal period of pregnancy?
Growth and physiological maturation of the structures created during the (v much shorter) embryonic period Period involving preparation for the transition to independent life after birth
When is pregnancy calculated from?
From the first day of the last menstrual period.
When is the organogenesis period?
The embryonic period. When the organs are being built and there is intense activity
When do we see significant increase in growth and weight of fetus?
Fetal period
In early pregnancy, what measurement can be used as a marker of fetal growth?
Crown to rump length in the pre-embryonic, embryonic and early fetal periods
Describe fetal growth in the embryonic period
intense morphogenesis & differentiation; little weight gain;
placental growth most significant
How does weight gain vary throughout the fetal period?
Early fetus - protein deposition
Late fetus - adipose deposition ( brown adipose)
How do body proportions change during the fetal period?
At 9 weeks, the head is approximately half the crown-rump length.
Later the trunk and limb growth accelerates.
Even at birth the head represents 1/4 of the length of body
How do we make assesssments of fetal well being?
- Fetal movements - should detect at 15/16 weeks, any changes in fetal movements
- Regular measurements of uterine expansion - symphysis-fundal height
- Ultrasound scan
What are the benefits of using obstetric ultrasound scan?
Safe assessment of growth and development of fetus
Early pregnancy = used to calculate age, rule out ectopic, number of foetuses
When is an obstetric ultrasound scan carried out and why?
Routinely carried out at 20 weeks to assess fetal growth (now big enough for assessment) and fetal anomalies
‘Anomalies scan’
How do we estimate fetal age?
Last menstrual period
Developmental criteria - more accurate
Why is LMP prone to inaccuracy?
Date of conception not always known
Variation of length and duration of menstrual cycle
What is the developmental criteria used to estimate fetal age?
Size against projected normal growth curve
When is crown-rump length used to date the pregnancy?
Between 7 and 13 weeks
What is an ultrasound scan in the first trimester used for?
To measure crown rump length
Check location
Number
Viability (heart beat)
In the second and third trimesters, what measurements are used assess fetal growth an dating?
Biparietal diameter - distance between the parietal bones of the fetal skull
Abdominal circumference
Femur length
- also useful for anomaly detecting, EDD
What key body structures are assessed during an ultrasound in T2/T3?
Neural tube ( brain, spinal cord ) Heart
What is the average brith weight?
3.5 kg
Under what birth weight suggests growth restriction?
2.5kg
Over what weight suggests macrosomia?
4.5kg