Fetal Growth

Question 1

External determination of foetal size?

Answer 1

Symphysis Fundal Height (SFH)

oDistance between pubic symphysis and fundus of uterus.

Question 2

Errors in values achieved from Symphysis Fundal Height?

Answer 2

 Values lower than they should be – wrong LMP (last menstrual period) date, baby lies in a transverse line, complications including oligohydramnios or baby ultrasound small for gestational age.

 Values greater than they should be – wrong LMP date, multiple pregnancy, maternal obesity, complications including molar pregnancies, fibroids, polyhydramnios, large baby for gestational age.

Question 3

Historical data on foetal size and hence growth (weight) came from what and why was this inaccurate?

What is the new method?

Answer 3

 Historical data on foetal size and hence growth came from miscarriages which data didn’t consider the possible causative relationship between low foetal growth leading to miscarriages – old data may be inaccurate.

oHence foetal growth (weight) measurements have mainly been replaced with in utero scanning data.

Question 4

Normal foetal growth – TWO factors are important for foetal growth (weight)?

Answer 4

o Genetic potential.

o Substrate supply.

Question 5

Ultrasound scanning – US scanning can identify the following?
And what are the combined measurements used for?

As a result what is US used to assess?

Answer 5

Biparietal diameter [head diameter]
Head circumference
Abdominal circumference
Femur length

These measurements Combine into Estimated Foetal Weight (EFW).

 Ultrasound scanning is mainly used to assess OVERALL FOETAL WELL-BEING (i.e. chromosomal abnormalities).

Question 6

US scanning measurements - what can be generated from this data?
[pic on last page]

Answer 6

Estimated Foetal Weight (EFW) thus Normative growth curves can be obtained.

Question 7

Due to the differences in people, customised foetal growth charts may be used instead of the normative growth curves - what are customised foetal growth curves based on?

Answer 7

o Based on foetal weight curves for normal pregnancies.
o Adjusted to reflect maternal
variation – i.e. mother weight.
o Optimised – with curves free from data influenced by pathological factors.

Question 8

Growth velocity = overall rate at which an infant gains weight - state weight gain at different weeks of development?
Hence when is the fastest velocity?

Answer 8

14-15 weeks = 5g/day.
20 weeks = 10g/day.
32-34 weeks = 30-35g/day.
>34 week = velocity decreases.

Fastest velocity is mid-third trimester.

Question 9

Normal foetal growth rates – characterised by three main phases?

Answer 9

o Hyperplasia – 4-20 weeks.
o Hyperplasia and hypertrophy – 20-28 weeks.
o Hypertrophy – 28-40 weeks – hence why mid-third trimester is greatest growth velocity.

Question 10

Dating the pregnancy?

• difficulty
• best method

Answer 10

o It is hard to date the pregnancy exactly as there are issues knowing the LMP (last menstrual period) date (i.e. planned vs. unplanned pregnancies, oral contraceptive use, etc.) but it’s important to get it right to classify gestational age.

o Best practice to date pregnancy – ultrasound – determining crown-rump length of foetus (end of 1st trimester – variations in foetal size are more limited at this stage so more accurate date).

Note: crown-rump length of foetus = measure of baby size from top to bottom.

Question 11

Influencing factors of foetal growth?

Answer 11

o Maternal factors influencing foetal growth:

o Feto-placental factors:

Question 12

Influencing factors of foetal growth - maternal factors?

Answer 12

Maternal factors influencing foetal growth:
 Poverty – more likely to be young (low birth weight) and be less educated on risks.
 Mother’s age – too young or too old can impact baby health.
 Drug use and alcohol.
 Smoking and nicotine.
 Diseases.
 Mother’s diet and physical health – MALNUTRITION is the most important factor in baby growth.
 Mother’s prenatal depression.
 Environmental toxins.

Question 13

What is the most important factor in baby growth?

Answer 13

MALNUTRITION

Question 14

Influencing factors of foetal growth - feto-placental?

Answer 14

 Genetic potential
 Gender – males tend to be bigger than females.
 Previous pregnancy – infants are heavier in the 2nd and subsequent pregnancies.
 Hormones – one important hormone is IGF-1 that acts to:
• Increase mitotic drive.
• Increase nutrient availability for tissue accretion.
Note: IGF-1 Little effect on tissue differentiation (this is mediated by cortisol).

Question 15

Define SGA – Small for Gestational Age?

Answer 15

infant has a birth weight <10th centile (AKA “Small for Dates”).

 A baby at term at 2,500g would be SGA but a baby of 2,500g ay 33 weeks’ delivery is normal.

Question 16

Define Intrauterine growth restriction?

Answer 16

o IUGR – failure of the infant to achieve its predetermined (genetic) potential for a variety of reasons.

Question 17

Define LBW – Low Birth-Weight, VLBW and ELBW

Answer 17

o LBW – Low Birth-Weight – <2,500g - ~7% of deliveries.
o VLBW – Very Low Birth-Weight - <1,500g - ~1% of deliveries.

o ELBW - <1,000g - ~0.2% of deliveries.

Question 18

Using the graph a baby at term at 2.5kg v.s a baby at 33 weeks delivery = 2.5kg?
[insert pic]

Answer 18

A baby at term at 2,500g would be SGA but a baby of 2,500g ay 33 weeks’ delivery is normal.

Question 19

It is important to determine between pre-term babies that are of a LBW and those that are IUGR - why?

Answer 19

IUGR (at a greater risk).

Question 20

Intrauterine Growth Restriction:
- describe axis
- 10th centile v.s 3rd centile
[insert pic]

Answer 20

 Age on x-axis and weight on y-axis.

 The 10th centile is most sensitive and the 3rd centile is most specific.
o 10th centile will capture all babies with IUGR but also those that are SGA.
 i.e. captures false +ve.
o 3rd centile captures IUGR but also misses some.

Sensitive = true possitive 
Specific = true negative

Question 21

What does the growth curve not take into account?

Answer 21

o No consideration of genetics.

Question 22

The term IUGR is only used for definite IUGR babies - what can be used to improve diagnosis accuracy?
[pic]

Answer 22

 The term IUGR is only used for definite IUGR babies.

o The growth charts are most useful for displaying serial estimates over time so diagnosis accuracy is higher.

Question 23

Outcomes of IUGR?

Answer 23

o IUGR is most common cause of still-born babies.

o Subsequent pregnancies may be affected by IUGR.

Question 24

When does IUGR occur in fetal development?

Answer 24

o Generally, develops in the 2nd and 3rd trimesters as the 1st stage focuses on embryology (up to 50g weight).

Question 25

Causes of IUGR?

Answer 25

Divided into 4 categories:
 Maternal medical factors – infection, pre-eclampsia, uterine abnormalities, etc.
 Maternal behavioural factors – i.e. alcohol.
 Foetal factors – i.e. multiple pregnancy.
 Placental factors – i.e. placental cysts, impaired trophoblast invasion.

Note understanding only: trophoblasts = cells very important in nutrient supply to placenta and foetus.

Question 26

IUGR and Pre-Eclampsia?

[pic]

Answer 26

 There is a close link between IURG and pre-eclampsia.
o Due to main cause of pre-eclampsia is diminished remodelling of spiral arteries by cytotrophoblasts. This causes decreased blood flow and hence decreased nutrient supply to the placenta and foetus.

Question 27

Pre-eclampsia symptoms?

Answer 27

Pre-eclampsia – hypertension and proteinuria.

[in pregnant women]