Methods of dating a pregnancy Flashcards
What is the purpose of dating a pregnancy?
- Monitor progress for mum and baby
- Educate mother, family, manage expectations and reassure
- Prepare the mother/ family and HC team
- early detection and intervention of any problems
- Look for prematurity/ long pregnancies
How long is the embryonic period?
When is the foetal period?
What are the three classes or term?
What is term split into? Why would we want to induce labour over normal term?
The embryonic period is the first 8 weeks.
Foetal period is 8 weeks to term. Term is split into further groupings of delivery between:
- Full term 37-42 weeks : Singleton 41 weeks completed/ twins 37 weeks.
- Full term classes as shorter for twins as the stress on the placenta is higher with two babies, and the risk of intrauterine death raises significantly with longer terms.
- Post 42 weeks –> induction from 41 weeks due to the risk of placental exhaustion
- Preterm 24- 37 weeks
Normally the terms are split into three trimesters.
When is a foetus considered viable?
Foetus is considered viable at 24 weeks.
Likely to change throughout medical career, babies in neonatal care even at 22 weeks.
What are the methods of dating a pregnancy?
1) LMP: Naegele’s rule –> assumes a 28 day cycle and uses the first day of the last menstrual period
Add 12 months then minus 3 months. (Basically add 9 months)
Then add 7 days to the first day of the LMP
(essentially add 40 weeks to the date of the last menstrual period)
(Dawn says dont worry about too much for the exam)
2) Early sonogram (ultrasound scan): CRL
UK standard is crown- rump length at early scan (if above 84 mm the gestational age should be estimated using the head circumference )
3) Symphysio- fundal height (From 24/40)
Separate growth chart, i.e for twins separate growth chart for each baby. Always measured from the top of the uterus body (fundus) down to the pubic symphysis.
all only establish an ESTIMATED date of delivery (EDD) , not the day
Many flaw with this method.
What is the key hormone produced during pregnancy required for maitenance of the early pregnancy?
How does it maintain pregnancy?
When is it first detectable?
What is its role in morning sickness?
Human chorionic gonadotropin (hCG) = glycoprotein hormone family member (along with LH/ FSH/ TSH)
Critical for rescuing the corpus luteum from involution and this maintains progesterone secretion by the OVARIAN GRANULOSA cells
hCG keep oestrogen and progesterone at app. levels until the placenta has developed enough to take over
hCG peaks at 8-10 weeks and plateaus to a lower level for the rest of pregnancy.
Progesterone is triggered by hCG/ Corpus luteum produced for 10 weeks until the placenta takes over.
Detectable in blood and urine 10 days post conception (after implantation)
Level double every 2 days –> Morning sickness
What is the “hormone of pregnancy”?
main role in pregnancy?
Other effects?
Hormone of pregnancy refers to progesterone.
It regulates the endometrial environment:
- Smooth muscle relaxant –> preventing uterine contractions
- can cause nasal congestion
- ureters dilate, bladder less tone (stress incontinence)
- gut- delayed peristalsis
- full stomach
- decreased vascular resistance and fall in BP -> dizzy/ fainting.
Oestrogen produced by what in the first 10 weeks of pregnancy?
Then by what?
What are the effects of oestrogen?
Oestrogen is produced by the corpus luteum until the placenta takes over by around 10 weeks.
Oestrogen stimulates:
- the adrenal gland and other organs/ bodily systems.
- increased appetite
- Skin changes -> spider naevi (due to increased oestrogen) and linea nigra (hyperpigmented line extending from pubic symphysis to umbilicus and above (fundus of uterus).
-
Breast feeding:
- induces myoepithelial contractibility -> ready for breast feeding
- Works with growth hormone to stimulate breast growth
- induces the secretion of prolactin –> prepares the breasts for lactation and has a tranquilising/ relaxing effect
What is relaxin?
What is its role in pregnancy?
what is an issue with too much relaxin?
- Relaxin is a hormone produced during pregnancy, highest in the 1st trimester
- in early pregnancy promotes implantation and placental growth
- relaxes the uterine muscles to prevent spontaneous abortion/ premature birth
- Relaxes arteries to support the increase in blood flow to the placenta and kidney (aids in excretion of waste metabolites)
-
Loosens the ligaments that hold the pelvis together:
- Issue of Symphysis Pubis dysfunction --> too much relaxin causes the ligaments of the pubic symphysis (cartilaginous joint) to become stretchy/ soft/ relaxed –> can lead to pubic bone separation (1% of pregnancies).
What is oxytocin?
What are its main functions?
Oxytocin is a hormone produced by the hypothalamus (magnocellular neurones) and is directly carried down the axon for release at the posterior pituitary.
Roles:
Helps the cervix to stretch, important in the induction/ triggering and maitenance of uterine contractions during labour.
Uterus becomes very sensitive to oxytocin during end of pregnancy.
Positive feedback mechanism, oxytocin release induces uterine contractions which in turn promotes further release, contractions increase in intensity and frequency.
Also involved in breastfeeding in the “Let down/ milk ejection” reflex –> suckling induces oxytocin release, which induces contraction of the myoepithelial cells.
What can be used to induce labour?
Oxytocin can be used to induce labour, synthetic oxytocin = Syntocinon
What is the main role of progesterone?
What is the main role of oestrogen?
What is required during pregnancy?
Main role of progesterone –> reduce muscle excitability and relaxation
Main role of oestrogen –> increase myometrial excitability
Therefore require fine balance between the two hormones.
What hormonal changes occur at near term/ onset of labour?
What is required for regular uterine contractions?
Near term there is a fall in progesterone and an increase in oestrogen
This induces an increase in myometrial excitability and stimulates prostaglandin synthesis.
Prostaglandins -> induce cervical ripening, which is the process of softening and dilating the cervix prior to the onset of labour
Oxytocin receptors and gap junctions are key factors in developing regular uterine contractions.
What is affected anatomically during pregnancy?
mechanical effects due to uterine enlargement:
bladder and ureters –> increase in frequency of urine
Gut –> heartburn
Diaphragm and lungs –> pushed up
Heart/ aorta/ vena cava –> compression
Skin/ muscle –> sweaty
Lumbar spine
What happens to the aorta and IVC in supine position?
Compression of the aorta and IVC in supine and lateral tilt position.
What 5 systems are adapted during pregnancy?
CVS
Blood
Respiratory system
Urinary/ renal
glucose metabolism
