Anatomy of pregnancy Flashcards
What does this describe: the space between the pubic symphysis, superior boarder of pubic crest, pubic tubercle, pectineal line, iliopubic eminence, arcuate lines, alar of sacrum & sacral promontory (S1 body)?
The pelvic inlet
What does this describe: wider antero-posteriorly; transverse ~11cm, AP = ~11.5; 25 degree angle to horizontal?
the pelvic outlet
What does this describe:
Separates true (above) & false (below) pelvis
60 degrees to horizontal (angle of inclination) - pelvis tilted, ASIS and pubic tubercle in same vertical plane
wide _transversely (_transverse ~13cm, AP (conjugate) ~12cm)
The pelvic inlet
What does this describe:
diamond shaped, pubic symphysis, inferior pubic rami, ischial rami, ischial tuberosity, sacrotuberous ligament. coccyx?
pelvic outlet!
[diamond shaped, pubic symphysis, inferior pubic rami, ischial rami, ischial tuberosity, sacrotuberous ligament. coccyx]
What route does the foetus take in the bony pelvis?
the pelvic axis
What muscles make up the pelvic floor?
Levator ani
- iliococcygeus
- pubococcygeus
- puborectalis
& coccygeus muscle on each side
+ anterior support by perineal membrane & muscles in deep perineal pouch
What shape / gender pelvis are these?
- android
- anthropoid
- gynaecoid
- platypelloid
- android = male
- anthropoid = long antero-posteriorally
- gynaecoid = female
- platypelloid = wide laterally
At what spinal level does the dura mater terminate at?
- S2
(cauda equina ~L1-L5; comes off conus medularris ~T12)
What changes to the uterus occur during pregnancy?
Uteral changes:
- Enlargement of uterus beyond pelvic cavity into the abdominal cavity – by 12 weeks (tri. #1)
- Increased vascularity & cellularity of uterus.
- Development of lower uterine segment.
- Relative shift of uterine tubes due to fundal enlargement.
What changes occur to the genitals during pregnancy?
- Softening of cervix & glandular hypertrophy.
- Blue tinge of lower genital tract due to Venous congestion
What changes occur to the skeleton during pregnancy?
- Softening & relaxation of ligamentous joints.
- Shift of centre of gravity→lumbar lordosis.
What changes occur to skin/tissues in pregnancy?
- Breast enlargement.
- Stretching of musculature of the anterior abdominal wall.
- –>Striae gravidarum from Rupture of connective tissue fibres - e.g. stretch marks
- Increased pigmentation eg
- linea nigra,
- cloasma,
- nipples.
during delivery how does the foetus:
1) enter
2) turn
3) extend
4) get shoulders out?
1) enters transversely
2) turns 90 degrees @ pelvic floow
3) extends neck when it reaches ischial spines
4) turns 90d again to get shoulders out
Where does the babys head need to fit between for delivery?
needs to fit between the symphysis pubis and sacrum - e.g. the biparietal diameter of the baby’s head ~9.5cm
- TF you want the babys occiput anterior (symphysis pubis) and head tucked in - makes smaller diameter
When is the uterus palpable O/E?
10-12wks
e.g. end of tri. #1
When does the uterus reach the umbilicus?
20wks
When does the uterus reach the xipisternum?
- at 36 wks
When can you start measuring fundal height (cm)?
roughly corresponds to gestational age in weeks between 16 - 36 weeks
What is the ideal/normal positioning for a foetus at term?
- longitudinal lie
- cephalic presentation
- L occiput –> anterior position
- head not yet engaged
- listen on shoulder for HR
- symphiso-fundal height ~consistent with age
At what stage of labour does the foetal head enter into the pelvic inlet transversely?
NB: remember the pelvic inlet is wider transversely
in the 2nd stage of labour
When is the foetal head described as “engaged”?
when the head lies in the true pelvis
e.g. 3/5ths of the head felt in the abdo
NB: the true pelvis is above the pelvic inlet and the false pelvis is below
What turns the babys head 90 degrees when they reach the pelvic outlet and why?
the levator ani (pelvic floor) turns the babys head 90 degrees
because the pelvic outlet has a greater AP diameter
At what anatomical landmark does the babys neck extend at when it reases?
the babys neck extends when it reaches the ischial spines
What does restitution refer to during labour?
restitution = the second 90 degree turn allowing the baby’s shoulders to be delivered
what injury becomes possible at “restitution” during labour?
upper brachial plexus (Erbs palsy) injury is possible at restitution
e. g. restitution = where the shoulders are able to be delivered due to the 2nd 90 degree turn
* NB:(the first was turning the head 90 deg. to go into the pelvic outlet that has a greater AP diameter)*
What is shoulder dystocia?
An obstetric emergency!
where the shoulders become stuck & the babys thorax is compressed
How do you feel for the position of the foetus? which is the widest part of the foetal head?
feel fontanelles!
anterior/posterior aka the longitudinal diameters are the widest part of the foetal head
What position of the baby during delivery does this describe?
- Baby’s face to sacrum
- Feel anterior fontanelle - at 6 o’clock (sacrum is 12 o’clock)
- Smallest diameter, one that presents optimally in labour
Occipito-anterior position (ideal)
- head flexion
- head deflexion
What position of the baby during delivery does this represent?
- -Baby’s face to pubic symphysis
- -Feel baby’s eyes on delivery
- -Anterior fontanelle at 12 o’clock
is delivery possible?
- Occipito-posterior position
(rotated this way by pelvic floor)
- Delivery possible
What position of the baby during delivery is this:
Feel baby’s eyes, nose & mouth on delivery
is it deliverable?
- brow presentation
- abdominal delivery necessary!
- e.g. occipito frontal diameter / mento-vertical diameter is big so –> c section
What does it mean if a baby is coming out with the sub-mento-vregmatic diameter?
- this means the ramus of mandible to centre of anterior fontanelle e.g.
-
FACE PRESENTATION!
- the head is completely extended unlike occipito-frontal/mento vertical (brow px)
- in theory vaginal delivery of face px is possible if the chin is anterior… TF if mento-anterior - allow vaginal delivery
- if mento-posterior = no more flexion is possible for baby to come out –> C-SECTION
What does it mean if O/E you feel the sacrum of the baby?
Breach position! - RCOG recommends all breach delivered abdominally
- can be complete = where knees are bend and feet and bottom are closest to birth canal
- incomplete = one of babys knees bent
- frank = both legs straight - just bum at bottom
- footling = one foot out other knee bent
Can deliver vaginally (if trained person around?) if FRANK/EXTENDED breach
How would you deliver a frank breach baby? (in theory)
- rotare baby so back is uppermost
- pull each leg out in turn
- let baby hang
- pull each arm out in turn
- then pull out head
How do you perform manual pelvimetry?
if fist fits between ischial tuberosities, baby will fit
What are the 2 types of cepalo-pelvic disproptortion and what do they mean?
- absolute
- the baby is never going to get out (maybe due to pelvic shape)
- relative
- the position of the baby is impairing delivery e.g. occipito-posterior ir de-flection of foetal head
What is looked for in a vaginal exam done during labour?
- station of presenting part in relation to the ischial spines
- dilation (if full dilation = cant feel cervix)
- feel sutures & fontanelles
What does -2 or +1 station mean?
the station is the presenting part in relation to the ischial spines
-2 = 2cm ABOVE ischial spines
+1 = 1cm below ischial spines
in feeling sutures and fontanelles:
what is moulding and caput?
caput is associated with moulding
-
Moulding = compression of head,
- AKA can feel sutures overlying eachother
- Caput = cant feel the sutures and fontaelles because of swelling from squashing of head–> occludes lymphatic/venous return –> swelling!
Why are fontanelles useful for guiding forceps?
fontanelles guide placement of forceps so as not to cause fractured skull
How are pelvic measures taken in obstetrics using imaging?
Why is this useful?
What parameters are looked at
- MRI is used - no radiation
- these measurement help predict the liklihood of successful vaginal delivery, they look at:
- Sagittal inlet and outlet,
- & inbetween: maximum transverse inlet diameter, bispinous outlet
What are the landmarks of sagital inlet and sagittal outlet seen on MRI for pelvic measures in obstetrics?
sagittal inlet: between sacral promontory (S1) & top of pubic symphysis
sagittal outlet: top of coccyx to inferior margin of pubic symphysis
Where does ectopic pregnancy most commonly occur?
in the ampulla
what conditions predispose to ectopic pregnancy?
anything kind of blocking/scarring the area?
- infection
- PID
- chlamydia
- appendicitis
- fibrosis from endometriosis
- coil!
What are the 3 main killers in pregnancy?
- Haemorrhage
- hypertensive disorders
- venos thromboembolism
What are the 4 grades of pelvic diaphragm tear?
- fourcechette & superficial perineal skin & _vaginal mucosa_l
- extends to perineal muscles and fascia
- extends to anal sphincter
- extends to rectal mucosa (e.g. breaks rectal wall)
NB: even if not torn, muscles weaken after surgery
What does this this describe:
incision made into perineal body to enlarge the vaginal orifice & allow the head of the fetus to pass through vagina?
Why is it done and what variations are there?
Episiotomy = done to cause less trauma to the peritoneum
- Median cut - incises the perineal body
- Medio-lateral - incision 45 degrees from the midnline
- –> avoids the perineal body,
- —> instead cuts the bulbospongiosus and superficial transverse muscle
Why can the foetal anomaly scan happen at 12 weeks?
at 12 weeks the foetus is fully formed and just needs to grow
e.g. brain, palate, heart chambers, femur length, head, abdomen
When is the early pregnancy USS scan done and what can it show?
early pregnancy USS scan 6-11w
scan shows if there is a:
- pregnancy/
- ectopic/
- age/
- foetal HR present
to determine the age of foetus = use crown-rump length
What are the 3Ps of labour?
- Passenger
- Passages
- Power
What factors of “passenger” affect labour?
- babys head measurements
- position
What factors of “passages” affect labour?
- engagement of foetal head
- boundaries of pelvis - inlet and outlet
- pelvic tilt
- levator ani muscles - the origin and insertion
- perineaum - implication & tears, episiotomies
What factors of “power” affect labour?
these involve things affecting the UTERUS - which contracts to expel baby
- Anatomy: corpus & cervix, 3 layers, oxytocin
- nerve supply: symp = lumbar splanchnic, para = pelvic splanchnic
- –> these are affected by:
- Epidural
- pudendal nerve block
- –> these are affected by:
What are the stages of labour?
- stage 1
- effacement & dilation of cervix (latent)
- after 3cm –> dilation occurs at 1cm/hr = active
- stage 2
- full dilation & expulsion of foetus
- Stage 3
- expulsion of placenta
What do these represent?
- Fully dilated
- Occipital position
- Ruptured membranes
- Contractions
- Empty bladder & episiotomy
- Pain relief
- Station (in relation to ischial spines)
the criteria for instrumental delivery!
What is a morula?
- >32 cell ball…
- too many cells to count
- Happens by day 4!
What is a blastocyst?
- the name of the morula once it has entered the uterus
- It is a ball of cells & cyst of fluid
happens by day 5!
What are the 3 layers of a blastocyst?
What do they do?
- trophoblast
- cells of blastocyst that invade endometrium and myometrium –> secrete bhCG
- chorion
- becomes placenta
- amnion
- becomes amniotic sac
Where does the early embryonic nutrition come from?
- reliant on cytoplasm inherited from oocyte
- & histiotrophic
- uterine secretions
- haemotrophic
- vascular contact between foetus and mum
When is the “window for implantation”?
Day 5-6 e.g. after the blastocyst has formed from the morula on D4 upon entering the uterus
When does the trophoblast produce bhCG?
at day 10
this maintains the corpus luteum which produces progesterone to prepare the endometrium for preg (= decidualisation) –> vital until placental steroidgenesis
(trophoblast supplys the embryo with nourishment and later forms the major part of placenta)
Its maximum amount of bhCG occurs at 9-11 weeks (only needed in early stages)
What can the bhCG levels produced by the trophoblast be used for?
- the basis of urinary pregnancy tests (qualitative measurement of beta subunit)
- if bhCG falls = dx miscarriage
- if bHCG rises too slowly = could be an ectopic pregnancy
What are the functions of the placenta?
- Steroidogenesis
- nutrition
- removal of waste
- barrier: against infection e.g. bacteria, viruses AND drugs
- antibodies
Why is the placenta useful for antibodies?
passes IgG on = passive immunity
NB: rubella gets across placenta
What steroids are produced in placental steroidogenesis?
- oestrogens
- progesterone
- Human placental lactogen (breaks down fats from mother to give for fuel to baby)
- cortisol
What nutrition does the placenta provide and what waste does it remove?
Gives: O2, carbs, fats, AA, vitamins, minerals
removes: CO2, urea, NH4, minerals
What contains a huge low pressure uterine blood supply, has a huge reserve in function e.g. can lose parts of the uterus and still function & has a huge surface area in contact with maternal blood?
the placenta!
What is the end purpose of these tissues invading the mothers uterus
- syncytiotrophoblast
- cytotrophoblast
- extraembryonic mesoderm
1 invades first then 2 then 3
they move down into linings and blend
the mesoderm differentiates into–> blood vessels and “pools” of maternal blood are found
the end point ==> mature branched vili
(theoretically there is TF no mixing of foetal/maternal blood: in practice a little bit always mixes)
What disorders of the placenta are there/what can they cause?
- Miscarriage: 15% pregnancies
- Ectopic pregnancy
- Hydatidiform mole: genetic, excessive trophoblastic activity (e.g. supposed to supply embryo with nourishment) can cause chorio-carcinoma
- Pre-eclampsia
- Placenta insufficiency: under-perfusion & growth restriction of the baby
- Transfer of drugs, toxins, infections to foetus
the trophoblast supplys the embryo with nourishment and later forms the major part of placenta.
What are the stages of trophoblast invasion ~10 when it produces bhCG?
- Early invasion
- decidualisation - thick layer of modified mucous membrane lining uterus
- stromal reaction - becomes oedematous/connective tissue
- angiogenesis - BV to provide nouishment etc
- erosion of the uterine decidua and glandular tissue by trophoblast = BV/mature villi left
