Reproductive Sytem Week 9

Question 1

Describe how gas exchange is promoted at the placenta

Answer 1

Low pO2 of foetal blood (4kPa compared to maternal 11-13 kPa of mother)
Increased maternal 2,3DPG due to respiratory alkalosis - shifts dissociation curve to the right - oxygen given up more easily
Foetal haemoglobin - HbF - higher affinity for O2 - doesnt bind 2,3 DPG as easily a HbA
Double Bohr effect - speeds up delivery of O2 - as CO2 passes into intervillous blood pH decreases - Bohr effect - decreasing affinity of Hb for O2 (maternal) - as CO2 is lost from foetal blood, its pH rises –> increasing affinity of Hb for O2
CO2 transfer - double haldane effect - the more oxygenated the blood, the less its affinity for CO2 (foetal blood), the less oxygenated the blood, the greater its affinity for CO2 (maternal blood) - no alterations in local CO2
- the progesterone stimulated hyperventilation causes maternal pCO2 to be lowered, allowing the foetal pCO2 to be relatively normal

Question 2

If the pO2 of the foetal blood is so low how does it get enough oxygen?

Answer 2

The Hb type if HbF which has a higher affinity for O2 than HbA - optimised for working in hypoxic environment
Foetal haematocrit is higher than in an adult (0.513-0.56 l/l compared to 0.4-0.54 l/l blood cell volume/total blood volume and 166-175g/l Hb/blood volume compared to 130-180g/l)

Question 3

What is HbF made up of?

Answer 3

2 alpha subunits and 2 gamma subunits

Question 4

When does HbF become the predominant form in the foetus?

Answer 4

From 12 weeks onwards until term

Question 5

Describe the foetal circulation

Answer 5

Receives oxygenated blood via umbilical vein
Bypasses the liver via the ductus venosus - liver would take too much O2
Lungs are non-functional - some blood passes to the RV, into the pulmonary trunk and through the ductus arteriosus and into the aorta - protects the lungs but allows a small amount to enter to enable development - pressure in pulmonary artery higher than aorta - high flow resistance of lungs
By-passes the lungs via the foramen ovale - by-passing right ventricle
Returns to placenta via umbilical arteries
Lower body relatively small and not that active metabolically

Question 6

What is the function of the ductus venosus ?

Answer 6

Shunts the blood around the liver
O2 saturation drops from 70% to 65%
Preserves O2

Question 7

What is the function of the foramen ovale?

Answer 7

Higher pressure in RA than LA –> Crista dividends (free border of septum secundum ) creates two streams of blood flow –> shunts majority of blood to the LA, some enters RV mixing with deoxygenated blood from SVC

Question 8

What is the saturation of the blood in the LA of the foetal heart?

Answer 8

60%
Oxygenated blood directly through foramen ovale
Receives some deoxygenated blood from pulmonary circulation
But brain and heart get lions share of oxygen (pumped through aorta to brain)

Question 9

What is the function of the ductus arteriosus?

Answer 9

Shunts blood from pulmonary trunk to the aorta - protects the lungs (although a small amount is allowed to pass through the lungs)
Joins aorta distal to the branches to the head and heart - minimises drop in O2 saturation

Question 10

Describe the foetal response to hypoxia

Answer 10

HbF and increased [Hb]
Redistribution of flow to protect supply to heart and brain
Heart rate slows in response to hypoxia to reduce O2 demand - chemoreceptors detect low O2 or high CO2 - vagal stimulation leading to bradycardia (opposite of adult response- vagal inhibition - tachycardia)
Chronic hypoxaemia - growth restriction, behavioural changes e.g. Less movement - impact on development

Question 11

Which hormones are required for foetal growth?

Answer 11

Insulin - permissive - promotes utilisation of nutrients
IGFI and II - most important
IGF II - nutrient independent - dominates T1
IGFI - nutrient dependent - dominates T2 and 3
Leptin - placental production
EGF, TNF-a

Question 12

What is the effect of malnutrition on foetal growth and development

Answer 12

Symmetrical or asymmetrical growth restriction
Nutritional and hormonal status during foetal life can affect health of child later in life - barker hypothesis - mechanism not well understood - placental adaptations to alterations in nutritional and hormonal status?

Question 13

What is the dominant cellular growth mechanism at 0-20 weeks?

Answer 13

Hyperplasia

Question 14

What is the dominant cellular growth mechanism at 20-28 weeks?

Answer 14

Hyperplasia and hypertrophy

Question 15

What is the dominant cellular growth mechanism at 28 weeks-term?

Answer 15

Hypertrophy

Question 16

Describe the purpose of the amniotic fluid, its volume and composition

Answer 16

Covers the foetus and embryo inside the amniotic sac
Provides protection
Contributes to development of the lungs
10ml at 8 weeks
1 litre at 38 weeks
Decreases following estimated date of delivery

98% water
Electrolytes, creatinine, urea, bile pigments, renin, glucose, hormone and foetal cells,lanugo (hair) and vernix caseosa (waterproofing)
Absorbs the water and electrolytes when swallowed
Debris accumulates in gut - meconium - debris from AF plus intestinal secretions including bile

Question 17

Describe the production and recycling of amniotic fluid

Answer 17

Early pregnancy - derived by dialysis of foetal and maternal extracellular components with some exchange occuing across the foetal skin
Foetal urinary tract - production by 9 weeks
- up to 800ml/day in T3
Some inhaled into lungs
Some swallowed into GI tract
Intramembranous (foetal and placental membranes) and transmembranous recycling

Question 18

What does a green stained amniotic fluid indicate?

Answer 18

Foetal distress - if in utero will be inhaled –> cause respiratory distress

Question 19

What is amniocentesis?

Answer 19

Sampling of amniotic fluid
Allows collection of foetal cells
Karyotyping
Safer than chorionic villus - lower risk of miscarriage

Question 20

Describe foetal bilirubin metabolism

Answer 20

During gestation clearance of foetal bilirubin is handled efficiently by the placenta - passes to mother
Foetus cannot conjugate bilirubin - immaturity of liver and intestinal processes for metabolism, conjugation and excretion
Physiological jaundice common - neonate not immediately able to deal with bilirubin

Question 21

Describe how growth changes between the pre-embryonic, embryonic and foetal phase

Answer 21

Pre-embryonic, embryonic and early foetal period - crown-rump length increases rapidly

Embryonic period - intense activity - organogenetic period

• Absolute growth very small - except placenta - placental growth most significant
• intense morphogenesis and differentiation

Foetal period - growth and physiological maturation of structures created in embryonic period

• preparation for transition to independent life after birth
• growth and weight gain accelerate
• early - protein deposition
• late - adipose deposition - preparation for life outside uterus
• body proportions change dramatically - at 9 weeks head is 1/2 of crown rump length - body length and limb growth accelerates thereafter —> 38 weeks - head 1/4 of entire length

Remember development proceeds in head to toe fashion throughout embryonic and foetal development

Question 22

Describe the antenatal assessment of foetal wellbeing

Answer 22

Mother - feels foetal movements - can detect changes
Regular measurement of uterine expansion - symphysis-fundal height
Ultrasound scan - safe
- can be used early in pregnancy to calculate age, rule out ectopic, check number of foetuses, assess foetal growth, foetal anomalies
-routinely carried out at 20 weeks - major body systems should have been built - assessment of structural integrity

Question 23

Describe how foetal age is estimated

Answer 23

LMP or fertilisation age - prone to inaccuracy - cycle length varies, break through bleeding at implantation, calendar months may have not been used

Developmental criteria - allow accurate estimation of foetal age with USS:

• CRL - measured between 7 and 13 weeks (less predictable after this time)- estimate date of delivery - at same time scan is used to check location, number and viability (heart rate/beat)
• biparietal diameter - distance between parietal bones of skull - used in combination with other measurements to date pregnancies in T2 and 3 - ventricular system can be checked
• abdominal circumference and femur length - used in combination with biparietal diameter for dating and growth monitoring - also useful for an anomaly detection- see spine, heart and stomach anomalies
• foot length
• 3 or 4 D USS - complimentary tool - not likely to replace 2D USS

-symphysis-fundal height - distance between symphysis pubis to top of uterus - measured with tape measure - 20cm at 20 weeks, 36cm at 36 weeks - alternatively assessed in relation to other structures such as umbilicus or xiphisternum - uterus palpable above pelvis after gestational week 12 - lag of 4cm or more of the fundal height is suggestive of intrauterine growth restriction/foetal growth restriction - variability arises from no. Of foetuses, volume of amniotic fluid, extent of engagement of head, lie of the foetus

Question 24

How are birth weights classified?

Answer 24

3500g - average
< 2500 g - suggests growth restriction
> 4500 g - macrosomia - maternal diabetes most Mormon reason
Many factors influence birth weight not all pathological - e.g. Genetics (mum small –> baby small)

Question 25

Why is accurate dating of foetal age important?

Answer 25

Can differentiate between different reasons for low birth weights e.g.
Premature
Constitutionally small
Suffered growth restriction - associated with neonatal morbidity and mortality

Question 26

Describe the foetal development of the respiratory system

Answer 26

Develop relatively late
Embryonic development creates only the bronchopulmonary tree - endoderm derivative - tracheo-oesophageal septum separates from oesophagus
Functional specialisation occurs in the foetal period
Major implications for pre-term survival - cant exchange oxygen
Weeks 8-16 - pseudoglandular stage:
- duct system begins to form within the bronchopulmonary segments created during the embryonic period –> bronchioles - not viable

Weeks 16-26 - canalicular stage:
- formation of respiratory bronchioles - budding from bronchioles formed during the pseudoglandular stage - may be viable towards the end- some terminal sacs have formed,more vascular

Weeks 26 - term - terminal sac stage:
- terminals acs begin to bud from respiratory bronchioles
Differentiation of Type1 and 2 pneumocytes –> surfactant - some primitive alveoli - surfactant formed from week 20 - increases significantly around week 30

Alveolar period - late foetal to 8 years of age (95% of alveoli are formed post-natally)

Breathing movements condition the respiratory musculature even though gas exchange continues to be performed at the placenta - fill with fluid - crucial for normal lung development - at birth lungs filled with amniotic fluid, together with secreted fluid - most is expelled during vaginal birth - any remaining is absorbed
Pulmonary resistance falls as alveoli open at first breath - blood flow increases in the pulmonary vessels

Threshold of viability - cannot deliver a baby before a certain point because the lungs will not be sufficiently developed to sustain life
- viability only a possibility once the lungs have entered the terminal sac stage of development - >24 weeks

Question 27

What is respiratory distress syndrome, when does it occur and how can it be prevented?

Answer 27

Insufficient surfactant production

Often affects infants born prematurely - lungs havent developed enough - lack of type II pneumocytes

If pre term delivery is unavoidable or inevitable e.g. Severe pre-eclampsia:
-glucocorticoid treatment of the mother –> helps speed up development and increases the likelihood that surfactant will be produced in the foetus before birth - have to be able to plan for it- window of opportunity

Question 28

Describe foetal development of the cardiovascular system

Answer 28

Arranged to ensure oxygenated blood collected by umbilical vein at the placenta is circulated around the foetus
Definitive foetal HR is achieved around 15 weeks - bradycardia associated with foetal demise

Question 29

Describe foetal development of the urinary system

Answer 29

Foetal kidney ascension and function begins in week 10 - metanephros
Urine major contribution to amniotic volume
Kidney not necessary for survival in utero but without it there is oligohydramnios - need amniotic fluid for normal lung development
Kidneys have lobulated form until 4-5 years of age
Glomeruli and some tubules present at 10 weeks, pelvis, calyces etc. By 23 weeks
Histological differentiation of cortex and medulla is almost complete by 8 months

In the foetus and infant the bladder lies in the abdominal cavity
Urine enters the bladder and is emptied into the amniotic fluid to be swallowed
Fills and empties every 40-60 mins in foetus - can be seen on USS - used clinically to assess foetal urinary function

Question 30

What does oligohydramnios indicate?

Answer 30

Too little amniotic fluid
Placental insufficiency e.g. Pre-eclampsia (membrane important early in development for amniotic fluid volume), foetal renal impairment (kidney takes over later)

Question 31

What is the significance of polyhydramnios?

Answer 31

Too much amniotic fluid
Indicates - foetal abnormality - e.g. Inability to swallow - neuronal, lung or GI defect
- sometimes idiopathic

Question 32

Describe the development of the nervous system

Answer 32

First to begin development and last to finish
Corticospinal tracts required for coordinated voluntary movements begin to form in the 4th month
Week 28 - characteristic gyri and sulci - appear as cerebellar hemisphere grow larger than the skull - cerebral hemisphere becomes largest part of brain
Histological differentiation of cortex in the cerebrum and cerebellum
Formation and myelination of nuclei and tracts
Relative growth of the spinal cord and vertebral column
Myelination of brain only begins in 9th month - corticospinal tract myelination incomplete at birth - evidenced by increasing infant mobility in the 1st year

No movement until 8th week
Thereafter large repertoire of movements develop - practising for post-natal life e.g. Suckling, breathing

Hearing and taste mature before vision - organ of corti well developed at 5 months, retina is immature at birth
Not sure when smell develops
Withdrawal from pain can be illicited at 15 weeks - thalamocortical projection do not reach maturity until week 29 - completion of myelination in corticospinal tracts not complete until post-natal period but msk movements are essential for foetal growth - Ascending tracts are present - though not myelinated - at 19 weeks

Brian accounts for 12% of body weight at birth -falls to 2% in adults

Question 33

What are the implications of the development of foetal movement in utero?

Answer 33

Quickening - maternal awareness of foetal movements from 17 weeks onwards (after development of voluntary movement) - movement is required for foetal growth

• low cost, simple method of ante-party’s foetal surveillance
• reveal those foetuses requiring follow-up

Question 34

Development of which systems has the greatest impact on viability and survival in the event of preterm delivery?

Answer 34

Respiratory

CNS

Question 35

What happens to the foetus at birth?

Answer 35

A combination of physical trauma and cold temperatures induces the neonate to take its first breath –> dramatic reduction in pulmonary vasculature resistance and a dramatic rise in arterial pO2
Causes left atrial pressure to rise in respect to right atrial pressure - closes the foramen ovale
Smooth muscle sensitive to high pO2 in the wall fo the ductus arteriosus contracts to close it - both shunts close off completely within a few weeks
Ductus venosus variably remains open for several days after birth - closes within two to three months - sphincter in the vessel constricts shortly after birth - directs blood through liver sinusoids - regulated by pO2 levels

Question 36

List some factors that have an impact on foetal growth

Answer 36

Maternal nutrition and health
Efficiency of placenta
Adequate utero-placental blood flow
Genetic factors
Maternal parity (primaparous mothers have smaller babies than multiparous)
Maternal habits (smoking, drug abuse etc.)
Race, maternal height, weight

Question 37

How may uteroplacental or foetoplacental circulations be investigated?

Answer 37

Doppler ultrasound

Question 38

Why is 20 weeks a good time in pregnancy to have the first (and sometimes only) ultrasound scan?

Answer 38

Organ systems are developed and can be visualised and anomalies can be identified
If anomalies are seen, the pregnancy is still early enough for possible intervention or termination if appropriate
The inherent error in these measurements increases with gestational age such that as a dating tool ultrasound becomes less accurate as the pregnancy proceeds:
1st trimester +/- 1 week
2nd trimester +/- 2 weeks
3rd trimester +/- 3 weeks

Question 39

List some uses of ultrasound in obstetrics

Answer 39

Determine presence or absence of intrauterine pregnancy (or ectopic pregnancy)
Determine gestational age and measure fetal growth (when compared against standard tables)
e.g., abdominal circumference (AC) biparietal diameter (BPD) crown-rump length (CRL) femur length (FL) head circumference (HC)
Estimate fetal weight Identify multiple pregnancies
Detect fetal anomalies (e.g., neural tube defects), placental anomalies (e.g., placenta praevia)
Measurement of amniotic fluid (Identify maternal pelvic anomalies) (Guide for needle in amniocentesis)

Question 40

Why might a transvaginal ultrasound be used in early pregnancy (8 weeks) in a woman who has had several early pregnancy losses?

Answer 40

To see foetal cardiac activity in the uterus - reassuring

Rules out ectopic pregnancy and early causes of loss such as blighted ovum

Question 41

Why are folic acid supplements recommended during pregnancy?

Answer 41

Reduce the risk of neural tube defects
Routine blood tests for alpha-fetoprotein are taken between 15-19 weeks gestation (levels at highest)
If elevated can be indicative of an open neural tube defect
Can simply indicate a multiple pregnancy
USS with optional amniocentesis is indicated

Question 42

When can the foetal heart beat be seen with trasnvaginal ultrasound, heard with Doppler stethoscope and heard with a plain stethoscope?

Answer 42

Transvaginal ultrasound - 5-6 weeks
Doppler stethoscope - 10-12 weeks
Plain stethoscope 18-20 weeks

Question 43

What is the average foetal heart rate at term?

Answer 43

140-160 beats per minute

Question 44

At what stage are foetal respiratory movements evident by sonography?

Answer 44

12 weeks onwards
34 weeks - occur in irregular bursts - rates up to 40-60/min, punctuated with periods of apnoea (including hiccups)
Foetal respiratory movements are diaphragmatic and cause movement of amniotic fluid into and out of the lungs

Question 45

At what gestational stage does surfactant start to be produced and how is this significant in prematurity?

Answer 45

Type II alveolar cells produce surfactant beginning around week 20 but increases significantly after 30 weeks - reaching significant levels about 34 weeks
Deficiency of surfactant leads to respiratory distress syndrome of the newborn - high risk in prematurity - steroid therapy given to women at risk of pre-term delivery - may reduce the risk of RDS by 50% - promoting the production of surfactant

Question 46

When does the uterus become an abdominal organ?

Answer 46

12 weeks - fundus palpable

Question 47

How is symphysis fundal height measured?

Answer 47

The height from the top of symphysis pubis to top of palpable fundus in cm correlates with number of weeks of gestation
Distance between symphysis pubis to top of uterus (i.e., fundus). It can be measured with a tape measure (e.g., 20cm at 20 weeks, 36 cm at 36weeks then, plateaus). Alternatively, the height of the fundus is assessed in relation to other structures such as the umbilicus or xiphisternum. The uterus is palpable above the pelvis after gestational week 12. A lag of 4 cm or more of the fundal height is suggestive of intrauterine growth restriction/fetal growth restriction.

Question 48

What are the sources of error for the symphysis fundal height?

Answer 48

Number of foetuses
Volume of amniotic fluid
Extent of engagement of head
Lie of foetus

Question 49

What does quickening feel like?

Answer 49

Fluttering

Question 50

What is the effect of multiparity on quickening?

Answer 50

multiparous woman may detect fetal movements earlier

Question 51

What pattern of growth restriction could you expect to find in the third trimester?

Answer 51

Asymmetric growth retardation in which there is “brain sparing”. The head (and indeed femur) continues to grow but abdominal fat and glycogen is diminished as fetus is compromised. Asymmetrical growth retardation is associated with poor maternal nutrition or decline in nutrient delivery to the fetus in the latter stages of pregnancy. This may be due to maternal or fetal factors but most often reflects compromise to the utero-placental unit. The growth restriction shows up mainly in the third trimester when nutritional demands and fetal growth are most rapid
Growth retardation earlier in pregnancy is more often related to genetic, or congenital problems or isolated insults to the development of the fetus.

Question 52

Why is foetal abdominal circumference a valuable measurement?

Answer 52

Measurement of fetal waist (at level of the umbilical vein) provides assessment of growth of fetal liver and amount of sub-cutaneous fat etc. Glycogen laid down in the fetal liver accounts for much of this growth.

Question 53

What is a biophysical profile (BPP)?

Answer 53

The BPP uses ultrasound and electrocardiography to document 5 parameters of fetal well-being relating to development and function of fetal organ systems and used to determine whether early delivery is required
Used when growth restriction suspected
Foetal movement - MSK, CNS
Foetal breathing movement - MSK, resp, CNS
Foetal tone - MSK, CNS
Amniotic fluid volume - Renal, GI, resp, uteroplacental
HR response to movement in the non-stress test - cardiovascular, autonomic nervous system
First four assessed by USS
Many factors may cause a reduction in the scores achieved including fetal sleep cycles, maternal dehydration or hunger, maternal sedation and fetal alcohol syndrome, as well as fetal compromise due to hypoxemia. The results have to be viewed in context of risk factors, earlier studies and sometimes repeat evaluations to determine whether urgent and /or early delivery is required.

Question 54

Normal CNS development is dependent on the production of which fetal hormone(s)
which if deficient cause cretinism in children?

Answer 54

Thyroid hormones (secreted from 12 weeks onwards, very little is derived from the mother)

Question 55

Why is asymmetrical growth restriction associated with oligohydramnios?

Answer 55

Nutritional deprivation / utero-placental insufficiency leads to decreased fetal urine production.

Question 56

What factors must you consider in deciding whether to allow a compromised fetus to
remain in utero?

Answer 56

Risks of compromise v risks of prematurity, particularly respiratory problems

Question 57

Prior to week 8, how is amniotic fluid produced?

Answer 57

Passage of fluid across the amnion and fetal skin (transudation)

Question 58

Which GI defects would lead to polyhydramnios?

Answer 58

Oesophageal atresia
Duodenal atresia
(Also, diaphragmatic hernia, anencephaly, inencephaly, hydrocephaly)

Question 59

Why does the foetal abdomen grow so large in poorly controlled maternal diabetes?

Answer 59

Much of the extra glucose will be laid down as glycogen in the
fetal liver (hence increase in fetal abdominal measurement).

Question 60

Other than gestational diabetes, what is a cause of macrosomia?

Answer 60

Post-term pregnancy

Question 61

In what instances might a foetus be identified as ‘at risk’

Answer 61

• maternal hypertension
• maternal heart or liver disease
• multiple gestation
• maternal diabetes
• where there is evidence of fetal growth retardation
• suspected oligohydramnios
• presence of placental abnormality
• post-dated pregnancy

Question 62

If you record neither foetal movements nor change in heart rate after a 30 minute non-stress test, should you be concerned?

Answer 62

No may be sleeping - repeat again - particularly after a meal

Question 63

What is meconium and how is it formed?

Answer 63

Typically, meconium are the first stools of a newborn baby – green, dark and sticky and composed of cellular debris, mucous and bile pigments. It is formed from the digestion products of amniotic fluid (cells and protein) the fetus has swallowed. The presence of meconium in the amniotic fluid is an indicator that the fetus has had an episode of distress.

Question 64

What are the advantages of a scalp electrode in monitoring foetal heart rate during labour?

Answer 64

Allows for continuous close monitoring of fetal heart rate regardless of maternal position.

Question 65

How can you decide on the lie and presentation of a foetus in early labour?

Answer 65

USS

Palpation

Question 66

What are the two types of foetal growth restriction?

Answer 66

There are two main types of growth restriction, SYMMETRICAL, in which growth restriction is generalised and proportional, and ASYMMETRICAL, in which abdominal growth lags and there is relative sparing of head growth. The latter tends to occur in the last part of pregnancy when maternal, fetal or utero-placental factors cause some deprivation of nutritional and oxygen supply to the fetus.

Question 67

When is a foetus defined as having a growth restriction and what are the consequences?

Answer 67

A foetus is regarded as having ‘growth restriction’ if his/her estimated weight is below the 10th percentile for his gestational age. Depending on the cause a fetus with growth restriction may be compromised in the uterine environment and require closer monitoring in order to allow the continuation of the pregnancy to term.