Methods Of Dating A Pregnancy & Maternal Physiological Changes During Normal Pregnancy

Question 1

What is dating a pregnancy important?

Answer 1

• Monitor normal progress of pregnancy
• Educate/reassure mum on expectations
• Early detection of problems so you can intervene
• Prepare mum/family/health care team
• Know if pregnancy is too short/prematurity or too long/post-dates

Question 2

What are 2 periods in pregnancy?

Answer 2

1. Embryonic: first 8 weeks

2. Foetal: 8 weeks-term

Question 3

What classes as a normal term pregnancy?

Answer 3

37-42 weeks (singleton 41 weeks completed but twins 37 weeks completed because otherwise there is a higher risk of intra-uterine death)

Question 4

What is an abnormal term in pregnancy?

Answer 4

Pre-term = 24-37 weeks

Post-term = 42+ weeks (induction from 41 weeks as placenta is tired out)

Question 5

How many trimesters are there?

Answer 5

1 = 1-12 weeks

2 = 13-28 weeks

3 = 29-40 weeks

Question 6

When can you have an abortion up until?

Answer 6

Age of liability = 24 weeks

Question 7

What are the 3 ways in which you can date a pregnancy?

Answer 7

1. Naegele’s Rule
2. Early sonogram
3. Symphysio-fundal height from 24/40 weeks

Question 8

What is Naegele’s rule?

Answer 8

Assumes a 28 day cycle and uses the first day of the last menstrual period (LMP) and adds 9 months and 7 days to it (plus or minus days resulting for differing cycle length)

Question 9

What is the early sonogram method?

Answer 9

Determine crown-rump length in mm from a early US scan - if >84mm the gestational age should be estimated using the head circumference

Question 10

How do you measure symphysio-fundal height?

Answer 10

At 24-40 weeks from top (uterine fundus) to bottom (pubic symphysis) to establish as estimated date of delivery (EDD) not the exact day using the customised growth chart (GC) - has many flaws

Question 11

Why do physiological changes occur in pregnancy?

Answer 11

Mechanical/hormonal affects effect all maternal systems giving typical pregnancy symptoms or changes that are essential for maternal/foetal health e.g. increased CO

Question 12

What is human chorionic gonadotropin (hCG) hormone?

Answer 12

Member of the glycoprotein hormone family (inc. pituitary hormones LH/TSH/FSH) detectable in blood and urine 10 days post-conception (after implantation) with levels doubling every 2 days with higher levels with more babies responsible for morning sickness - levels peak at 8-10 weeks and plateaus to a lower level for the rest of pregnancy

Question 13

What is the function of human chorionic gonadotrophin (hCG) hormone?

Answer 13

Rescues the corpus luteum from involution which maintains progesterone and oestrogen secretion by the ovarian granulosa cells keeping oestrogen/progesterone at appropriate levels until placenta has developed enough to take over after 10 weeks

Question 14

What is progesterone?

Answer 14

The hormone of pregnancy maintaining an appropriate endometrial environment and a SM relaxant that also:

• Prevents contractions
• Causes nasal congestion
• Dilates ureters
• Decreased bladder tone
• Delayed gut peristalsis so stomach is fuller
• Decreases vascular resistance
• Decreases BP so causes dizziness/fainting

Question 15

What does the foetus itself do to the mother?

Answer 15

Stimulates adrenal glands and other organs/bodily systems causing the mother to have:

• Increased appetite
• Skin changes
• Spider veins
• Increased contractability of the myometrium

Question 16

What does oestrogen do?

Answer 16

Works with GH to mediate breast growth and induces the secretion of prolactin which prepares the breast tissue for lactation also having a tranquilising effect

Question 17

What is the function of relaxin?

Answer 17

Loosens the ligaments that hold the pelvis together, relaxes uterine muscle and relaxes arteries to support increased blood flow - why symphysis pubis dysfunction can occur (1% of pregnancies)

Question 18

What are the functions of oxytocin?

Answer 18

AUGMENTS LABOUR as uterus becomes sensitive to it towards the end of pregnancy to induce labour, help cervix to stretch and stimulates uterine contractions but it also makes myoepithelium cells contract to produce “let down” reflex (milk squirts out)

Question 19

What is synthetic Oxytocin called?

Answer 19

Syntocinon

Question 20

How must progesterone and oestrogen be balanced for labour?

Answer 20

Progesterone reduces muscle excitability whereas oestrogen increases myometrial excitability so at the onset of labour there is a fall in progesterone and increase in oestrogen which induces myometrial excitability and stimulates PG synthesis

Question 21

What are the key factors in developing regular uterine contractions?

Answer 21

Oxytocin receptors (OTR)

Gap junctions

Question 22

What anatomical systems are affected in pregnancy?

Answer 22

Uterus 
Bladder/ureters (increased freq. of urination)
Gut (heartburn)
Diaphragm/lungs
Heart/aorta/vena cava
Skin/muscle (sweaty)
Lumbar spine

Question 23

What position must you lay a pregnant lady in? Why?

Answer 23

Lateral tilt position as her aorta and IVC will be squashed otherwise which may affect baby and mum making her feel faint

Question 24

What are the 5 major systems that maternal adaptations occur in?

Answer 24

1. CVS
2. Blood
3. Respiratory
4. Urinary/renal
5. Glucose metabolism

Question 25

What happens to the cardiovascular system (CVS) in pregnancy?

Answer 25

Occurs early by 12-16 weeks:

• Heart enlarges due to increased workload
• Apex displaced up and laterally (4th ICS)
• Increased CO from 5 to 7 litres per. min (more in labour)
• HR increases 10-15bpm
• SV increases
• Vascular resistance falls
• MAP falls by about 10mmHg and rises to normal as term approaches

So at antenatal check ask about Hx of CVS disease

Question 26

What happens to the blood in pregnancy?

Answer 26

• From 10th week plasma volume expands by 45% and total RBC volume increases by 15% so Hb, haematocrit and RBC all fall
• By 28-34 weeks physiological anaemia occurs via haemodilution
• Circulating BV increased 50% by term
• Toleration of blood loss increased (due to birth)
• Many coagulation changes that are pro-thrombotic (clotting time decreases)

So check nutrition/exercise/iron/anaemia/regular blood tests/advice/travel/Hx of thrombosis at antenatal check

Question 27

What is the average blood loss at birth?

Answer 27

250ml with vaginal delivery (more with C-section)

> 500mls = post-partum haemorrhage

Question 28

What happens to the respiratory system in pregnancy?

Answer 28

• Diaphragm pushed up and ribs flare to compensate; increased alveolar exchange, MV, TV but slight drop in pCO2
• Increases mucosal engorgement due to plasma volume expansion; epistaxis
• Increased RR, maternal awareness (SOB) and mild resp. alkalosis

So check for Hx of resp. disease/smoking in antenatal check

Question 29

How does oxygen consumption change over pregnancy?

Answer 29

+35% during due to increased needs of foetus, uterus and placenta

+40% in stage I of labour

+75% in stage II of labour

Question 30

What happens to the urinary/renal system in pregnancy?

Answer 30

• Increased renal size
• Changes in RAAS
• Promote plasma expansion
• Renal plasma flow and GFR increased
• Creatinine clearance increased
• Slightly lower absorption thresholds/glucose/protein
• Increased risk of infection due to dilated urethra/ureters and stasis

So check for Hx of renal disease, urinalysis, BP, bloods and oedema in antenatal check

Question 31

Why is pregnancy diabetogenic?

Answer 31

Placental hormones e.g. placental lactogen, human growth hormone, cortisol and progesterone cause:

• Increased appetite/fat deposition
• Increased insulin levels and resistance
• Post-prandial glucose levels rise

This facilitates transfer to baby but adaptive capacity of pancreatic insulin output may be overwhelmed causing gestational diabetes (GDM)

So do a risk assessment, check nutrition/exercise and screen for GDM in antenatal check

Question 32

What are the 2 major consequences that can occur if adaptations dont occur sufficiently?

Answer 32

1. Pre-eclampsia

2. GDM

Question 33

What is gestational diabetes mellitus (GDM)?

Answer 33

Occurs in ~4% of pregnancies because there is not enough insulin to counteract the diabetogenic hormones which increase in pregnancy and also because obesity is increasing in the population and it increases risk of:

• GDM in future pregnancies
• T2DM in later life
• Macrosomia in baby (must induce at 37 weeks or shoulder dystocia risk)

Question 34

What is pre-eclampsia linked to?

Answer 34

Inadequate placentation

Question 35

What are the 3 clinical crucial signs of pre-eclampsia?

Answer 35

1. HBP due to failure of reduced vascular resistance and renal adaptation to pregnancy
2. PROTEINURIA due to leaking of glomeruli
3. OEDEMA because there is leaking of capillaries with increased volume

Question 36

When doing antenatal checks how can you asses risk of pre-eclampsia?

Answer 36

1. Assess risk factors, advise and educate the mother
2. BP every visit in same position
3. Urinalysis every visit checking for protein
4. Check for oedema

Question 37

What do early antenatal visits include?

Answer 37

Establish partnership care
Check medical/OB history
Agree anticipated due date
Discuss/arrange screening and pattern of care
Discuss ICE and lifestyle

Question 38

What do later antenatal visits include?

Answer 38

Monitoring of maternal adaptions/changes
Monitoring of foetal growth and development
Educate/advise/prepare

Question 39

What is the aim of antenatal care?

Answer 39

Support and ensure normal progression of pregnancy and birth whilst identifying risk factors that could affect maternal and foetal outcomes