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Flashcards in obstetric physiology Deck (51):

how much does CO increase by during pregnancy?



what is the primary CV change in pregnancy?

peripheral vasodilation--> SVR falls


why does GFR increase during pregnancy?

increased CO + increased renal flow --> GFR increases


what does the supine hypotension syndrome of pregnancy refer to?

in late gestation (e.g 3rd trimester), the uterus may compress the vena cava reducing venous return--> reduced CO. usually the maternal compensatory response is to increase sympathetic tone.

in 10% of women, this compensatory response is inadequate and there is a significant fall in BP --> LOC


why are pregnant women susceptible to APO?

due to reduced colloid oncotic pressure/ pulmonary capillary pressure gradient


why is pregnancy a hypercoagulable state?

to reduce risk of postpartum bleeding


why do DVTS during pregnancy mostly arise from the left leg?

because of compression of the left iliac vein by the left iliac artery and ovarian vein


why do we get gastric reflux and constipation during pregnancy?

progesterone reduces LOS tone and reduces GI motility


why are there rapid blood volume changes during labour?

Valsalva (pushing)
epidural can cause hypotension due to reduced LV load


where does most of the fetal cardiac output go to in utero and why?

vast majority of fatal blood from right side of the heart goes through the PDA --> left ventricle (bypasses the lung)

only 10% CO go into the fetal lungs

Most CO goes to the placenta and head of baby


what respiratory adaptations occur in a neonate soon after birth?

Pulmonary vascular resistance decreases (pulmonary arterioles dilate) -> leads to increased pulmonary blood flow --> closure of the ductus arteriosus

Blood O2 levels increase as blood flows through the lungs


why is the critical period for viability around 24 weeks gestation?

before 22 weeks, undeveloped lungs--> no alveoli--> no gas exchange is possible so if born, very hard to resuscitate and impossible to survive


why does the body weight of a newborn drop initially?

loss of excess body water --> decreased body weight


what are the 3 shunts present in foetal blood circulation?

1. ductus venosus
2. ductus arteriosus
3. foramen ovale



1. Umbilical arteries and umbilical vein constrict, collapse and disappear
2. less blood going to the right side of the heart
3. Left side of heart pressure > right side pressure and as FO is one way valve, it closes

so overall:
1. placenta removed
2. Shunts close
3. PVR falls
4. Parallel--> series


what is the difference between foetal hb and adult hb?

foetal hb has a higher affinity for O2, shifting the Bohr curve to the LEFT


how might we cause anaemia in a newborn?

iatrogenic- blood sampling


why might a newborn delivered by c-section experience transient tachypnoea or resp distress?

usually adrenaline released during normal vaginal birth ceases production of fetal lung fluid.

During c-section, less adrenaline will result in excess fetal lung fluid --> resp distress


what are the constituents of surfactant?

lipoprotein complex

90% phospholipid
10% protein


what does the 'Head's paradoxical reflex' mean?

when we try to give PEEP to infants, paradoxically, it causes the baby to start breathing

whereas normally it wouldn't in adults


what do we think about if we have a pregnant woman with polyhydraminos?

indicates that a foetus is not swallowing-->

Obstructive causes:
-oesophageal atresia

OR a neurological cause when the baby is not swallowing


describe the physiological mechanism of aorto-caval compression? and how might it be affected by an epidural?

aorta and IVC may be compressed by gravid uterus when the woman lies prone

IVC compression begins in the 2nd trimester.

usually, this results in a compensatory tachycardia, vasoconstriction and diversion of blood through the epidural and azygous system

however when an epidural is put in:
it will cause decompensatory bradycardia, nausea, sweating and fainting.


why are pregnant women in a hypercoagulable state?

reduced platelets
increased clotting factors
plasminogen and anti-thrombin 3 decreases

this is a physiological response to prevent haemorrhage during pregnancy and labour


why are pregnant women predisposed to become peripherally/pulmonary oedematous?

reduced plasma oncotic pressure --> extravasation of fluid to third spaces


why is post-delivery the period of highest risk for CV events in the mother?

Increase after load, and venous return after loss of placental shunt--> highest risk of heart failure


when is the woman most at risk for thromboembolism in the peripartum period?

up to 5 days post delivery


why do pregnant women desaturate quickly?

smaller O2 store by reduced FRC (functional residual capacity) and greater rate of O2 consumption


why might GA be an issue in pregnant women?

high risk of aspiration


what are some concerns about intubating a pregnant woman?

pregnant women will rapidly desaturate if apnoeic

pregnant women are at increased risk of aspiration


what do obstetricians refer to when they talk about the 'membranes'?

fused chorion and amnion= membranes


why do we see a 'physiological anaemia' in pregnant women?

high blood volume state--> dilutional effect of Hb


describe the changes in body composition from a baby in utero to at birth and 1 yr post birth?

as a baby progresses in utero to term at birth, and then 1 yr post birth:

ECF decreases markedly
ICF increases markedly
Fat increases slightly
Solid increases very slightly


how many umbilical arteries/veins are there during pregnancy?

2 x umbilical arteries

1 x umbilical vein


describe the fetal blood circulation during antenatal period?

1. ductus venosus- shunts blood from placenta across the liver to IVC (Right atrium of heart)
2. blood is shunted away from the lungs through ductus arterioles connecting the pulmonary artery and aorta
3. bc of the high pressure in the right side of the heart, blood flow shunts through the foramen ovale to the left side and out through the aorta

from the left side of heart + aorta--> blood goes to the placenta, brain, rest of fetal body


how is fetal lung fluid extravasated during delivery so that the baby can now start breathing post delivery?

1. labour uterine contractions or the process of labour in general increases adrenaline--> adrenaline switches OFF fetal lung fluid production

2. vaginal delivery--> vaginal canal physically squeezes the fluid out from the fetal lungs

3. lymphatic drainage


which cells secrete bHCG?

trophoblast cells


as pregnancy is a hypercoagulable state, how do we manage prophylaxis of thromboembolism in high risk women?

daily low molecular weight heparin until labour, and then recommencing 6 hours postpartum


what are some thrombophilias you should watch out for in women who become pregnant?

anti thrombin 3 deficiency
factor 5 leidin deficiency
protein S and protein C deficiency


when does the lower uterine segment form in pregnancy?

around 26-27 weeks gestation


what is the main hormone which mediates uterine involution post delivery of baby?



what is the normal contraction rate in active adequate labour?

~4 contractions per 10 mins


what does tachysystole refer to, and what might it indicate?

Tachysystole is defined as more than five contractions in 10 minutes, averaged over 30 minutes. If tachysytole occurs, documentation should note the presence or absence of fetal heart rate (FHR) decelerations.


describe the attitude of a baby's head as it descends through the pelvic inlet

Attitude refers to the position of the head with regard to the fetal spine (the degree of flexion and/or extension of the fetal head). Flexion of the head is important to facilitate engagement of the head in the maternal pelvis. When the fetal chin is optimally flexed onto the chest, the suboccipitobregmatic diameter (9.5 cm) presents at the pelvic inlet


what do we mean by occiput anterior, right occiput anterior, left occiput anterior and occiput posterior of the baby's head?

For cephalic presentations, the fetal occiput is the reference. If the occiput is directly anterior, the position is occiput anterior (OA). If the occiput is turned toward the mother’s right side, the position is right occiput anterior (ROA).

occiput turned towards maternal left side--> LOA
occiput facing the sacrum= occiput posterior OP


what are the classical signs of placental separation?

(1) lengthening of the umbilical cord, and (2) a gush of blood from the vagina signifying separation of the placenta from the uterine wall.


what is the key difference between the composition of the lower uterine segment and upper uterine segment?

Like the cervix, the LUS has a fibromuscular composition and is easily recognised as it is covered by loose peritoneum. In contrast, the upper uterine segment (UUS) is thicker, muscular and covered by a serosal layer that is firmly adherent to the underlying muscularis


what hormones mediate changing of the pelvic outlet during labour?

progesterone and relaxin


what are the cardinal movements of a longitudinal lie cephalic baby during labour?

1. increased flexion of the baby's head as it descends into the pelvic outlet with each uterine contraction
2. internal rotation of the head--> occiput at the pubic symphysis usually
3. Crowning of the head
4. delivery of the head via full extension
5. restitution (external rotation) 1/8 of a circle
6. anterior shoulder descends and rotates internally
7. delivery of the anterior shoulder
8. Lateral flexion and delivery of the posterior shoulder


what is the narrowest diameter of the fetal skull?

submentobregmatic/suboccipitobregmatic diameter of 9.5cm

we would prefer suboccipitobregmatic as submentobregmatic is a face presentation


what does cervical effacement mean?

thinning of the cervix during labour


why is the occipital posterior diameter less favourable than occipitoanterior presentation during delivery?

fetal head is extended and hence there is a wider diameter through the pelvis--> more likely to obstruct