Methods of dating a pregnancy and maternal adaptations Flashcards
Why is accurate dating of a pregnancy important?
Monitor the normal progress of pregnancy (both for mum & baby)
Educate mum / reassure / expectations
Early detection of problems in mum or baby / intervention
Prepare mum / family / health care team
Know if pregnancy is too short / possible prematurity
Know if pregnancy is too long / post dates
How long do the three trimesters last?
1st: 1-12 weeks
2nd: 13-28 weeks
3rd: 29-40 weeks
What is term, preterm and post term in pregnancy?
Term: 37-42 weeks
Preterm: 24-37 weeks
Post-term: 42+ weeks
What are the 3 major ways of dating a pregnancy?
1) Naegele’s Rule.. assumes a 28 day cycle and uses first day of last menstrual period (LMP)
2) Early ultrasound scan, crown rump length (CRL at 12 weeks)
3) Measuring of symphysio fundal height from 24 weeks
How does Naegele’s rule work?
Add 9 months Add 7 days to first day of LMP (plus or minus days from resulting EDD for differing cycle length) e.g. 6 days for a 27 day cycle 7 days for a 28 day cycle 8 days for a 29 cycle 9 days for a 30 day cycle
Sheeya comes to see you and she reports the following:
Regular 28 day cycle
LMP 7th September 2019
What is her EDD (Estimated delivery date)?
14th June 2020
add 9 months and 2 days
Kata comes to see you and she report the following:
35 day cycle
LMP 27th January 2020
What is her EDD?
10th Nov 2020
Add 9 months and 14 days
What happens at the 12 week scan that can change the EDD?
Crown-rump length (CRL)
(If above 84mm, gestational age should be estimated using head circumference)
if this differs more than 7 days from the Naegele’s rule then EDD will be adjusted
How do you measure the symphysio-fundal height? (SFH) hint: top down
Tape measure from top of fundus to top of symphysis of pubis
What maternal anatomical changes are there in pregnancy?
Mechanical effects as uterus enlarges Bladder / Ureters (frequency of urine) Gut (heartburn) Diaphragm / Lungs Heart / Aorta / Vena cava Skin / Muscle (sweaty) Lumbar spine
How do we check a pregnancy woman’s BP? What is the best position for her mum and baby?
Tilt woman on left side!
In the supine position - compression of aorta and IVC
What hormonal changes occur in pregnancy? What physiological changes occur in pregnancy?
First trimester: HCG - morning sickness
Second/Third trimester: Progesterone dominates/ oestrogen also high
Progesterone= Smooth muscle relaxant (varicosities, constipation)
Ureters-Dilated; Bladder-less tone
Gut-delayed peristalsis; full stomach
Decreased vascular resistance; fall in BP, dizziness, fainting
Skin-pigmentation.. Dark nipples; linea nigra
Human placental lactogen….glucose metabolism
Prolactin…preparing for lactation
How do levels of progesterone and oestrogen maintain the pregnancy?
Progesterone reduces muscle excitability by increasing ca binding thereby reducing free intracellular ca. Oestrogen increases myometrial excitability. It’s a fine balance.
What happens to oestrogen and progesterone levels at the onset of labour?
Near term, there is fall in progesterone level and an increase in oestrogen this induces myometrial excitability and stimulates prostaglandin synthesis and increased oxytocin receptors and the formation of gap junctions.
List the major changes in maternal physiology during a normal pregnancy
Cardiovascular System Blood Respiratory Urinary / renal Glucose Metabolism
