Methods Of Dating A Pregnancy Flashcards
Why is dating a pregnancy important?
Monitors the normal progress of pregnancy for both mother and baby
Educates mum/reassures
Early detection of problems = intervention
Prepare mum/family/healthcare team
Know if the pregnancy is too short/possible prematurity
Know if the pregnancy is too long/post dates
What are the normal weeks of pregnancy?
Embryonic period = first 8 weeks
Foetal period = 8 weeks to term
Term 37-42 weeks
Pre-term 24-37 weeks
Post term 42+ weeks
What are the 3 trimesters of pregnancy? When is induction from?
Induced from week 41
Week 1-12
Week 13-26
Week 27-term
What week is the first scan of gestation?
Week 12
At what week is term for twins and why?
Week 37
Placenta getting tired
Chance of intrauterine death increases
What are the 3 different trimesters?
1st trimester: 1-12 weeks
2nd trimester: 13-28 weeks
3rd trimester: 29-40 weeks
What’s Neagele’s rule of dating a pregnancy? What do you need to know?
Assumes 28 day cycle and uses the FIRST DAY fo the last menstrual period
Then add 12 months and minus 3 months
Then add 7 days to first day of last menstrual period
(Basically add 9 months 7 days)
How can you use scanning to date a pregnancy?
Early sonogram at 12 weeks
Estimated gestational age using crown-rump length in early scans, then head circumference
When can you estimate date of delivery using symphysio-fundal height?
From week 24/40
Measure top down - from fundus of uterus to pubic symphysis and then use a chart
What’s hCG and its roles? When is it detectable in blood?
Human Chorionic Gonadotrophin hCG = glycoprotein
Critical for preventing corpus luteum from involution and maintains progesterone secretion by ovarian granulosa cells
Maintains oestrogen and progesterone levels until placenta takes over
Detectable in blood and urine 10 days post conception (after implantation)
Level doubles every 2 days = causes morning sickness
When do hCG levels peak?
At 8-10 weeks and then plateau for rest of pregnancy
What’s the main hormone in pregnancy following hCG?
Progesterone is triggered by hCG/corpus luteum
= smooth muscle relaxant to prevent uterus from contracting
What are the smooth muscle relaxant roles of progesterone in pregnancy?
Prevents uterus contractions Nasal congestion Dilates ureters Less tone in bladder Gut-delayed peristalsis Full stomach Decreased vascular resistance Fall in BP Dizziness Fainting
What are the roles of oestrogen on the foetus and mum during pregnancy?
In foetus: stimulates adrenal gland and other body systems
In mum: increased appetite, skin changes, spider veins, contractibility of myometrium
Mediates breast growth
What’s the role of prolactin in pregnancy?
Prepares breast tissue for lactation and tranquilising effect
What’s the role of Relaxin?
Loosens the ligaments that holds the pelvis together, relaxing uterine muscles, relaxes arteries to support increased blood flow
What’s symphysis pubis dysfunction?
Cartilaginous joint located between right and left sides of pubic bone
Connective tissue
Relaxin causes ligaments around SP become stretchy, soft and relaxed
Pubic bone separation in 1% pregnancies
What does Oxytocin do in pregnancy?
Helps cervix to stretch
Makes myoepithelium cells contract to produce the let down reflex
Uterus becomes sensitive to oxytocin towards the end of pregnancy
Syntocin (synthetic form) used to induce labour to stimulate uterine contractions
What’s the progesterone/oestrogen balance?
Progesterone reduces muscle excitability
Oestrogen increases myometrial excitability
Near term there’s a fall in progesterone levels and increase in oestrogen = stimulates ripening of the cervix/prostaglandin synthesis
What receptors are key factors in developing regular uterine contractions?
Oxytocin receptors and gap junctions
Why is it important for pregnant women not to lie on their back?
Can compress aorta/IVC = mum can feel faint/low bp
What adaptations occur in the CVS during pregnancy?
Heart enlarges due to increased workload - apex displaced up and laterally (4th ICS)
Increased cardiac output & SV
Fall in vascular resistance
MAP falls by about 10mmHg
Occurs by 12-16 weeks
What are adaptations to blood during pregnancy?
Plasma volume expands from 10th week
Red blood cell mass increases by 15% but Hb, haematocrit and RBC all fall
= normal to have physiological anaemia by 28-34 weeks
Circulating blood volume increases by 50% at term
Toleration of blood loss is increased ready for birth
Blood becomes less coagulative = pro-thrombotic (clotting time decreases)
What parameters of a FBC are important to measure in an ante-natal check?
Nutrition Exercise Iron Anaemia Regular blood tests Advice Travel Hx of thrombosis
