Pregnancy Flashcards
What does ‘6 weeks pregnant’ mean in terms of gestational age and embryonic age?
Gestational age = 6 weeks (since LMP)
Embryonic age = 4 weeks (since conception)
What is the embryonic period defined as?
Up to 8 weeks
What is the fetal period defined as?
After 8 weeks
When does implantation begin?
Day 6/7 (after conception)
When is implantation complete?
Day 10
What is the ‘implantation window’?
The period in which implantation must occur (between days 20 and 24 of normal menstrual cycle)
What is the essential condition for implantation?
Low oxygen tension (remains until 16 weeks)
What causes the low oxygen tension in the first 16 weeks?
Trophoblast cells migrate into the spiral arteries and plug them
This blocks maternal blood flow to the placenta
What kind of nutrition does the foetus rely on for the first 16 weeks before the placenta development is complete?
Anoxic histiotrophic nutrition (diffusion)
What are the 3 stages of implantation?
- Apposition
- Attachment
- Penetration
What occurs during apposition?
Progesterone gets endometrium ready for fetus.
Becomes rich in glands, capillaries and stroma
What occurs during attachment?
Pinopodes from endometrium and microvilli on trophoblast help attachment
What molecules does penetration during implantation involve?
Prostaglandins (mediated by COX1 and COX2)
What do the uterine glands produce?
Lots of hormones that stimulate growth of embryo, e.g. VEGF, hCG.
Which 2 layers does the outer cell mass form?
- Synctiotrophoblast (outer layer, multinucleated)
2. Cytotrophoblast (inner layer, mononuclear)
Where is hCG produced?
Synctiotrophoblast
Where does hCG act?
On corpus luteum (positive feedback) to sustain progesterone levels
–> prevents menstruation and promotes decidualisation
What is the relationship between uterine microbiome and implantation?
Microbiome affects implantation
Recurrent miscarriage lady likely to have abnormal uterine microbiome (more anaerobic bacteria)
How can pre-eclampsia be diagnosed?
Doppler screening of the uterine artery
What are the risk factors for pre-eclampsia?
- previous history
- multiple gestation (twins etc)
- chronic hypertension/ diabetes etc
- obesity
- family history
- first pregnancy
What prophylaxis for pre-eclampsia is given if patient is high risk?
Aspirin should be given in first trimester
Which molecule is a good diagnostic indicator of pre-eclampsia?
Placental growth factor
What causes pre-eclampsia?
Placenta does not develop properly due to blood vessels supplying it
When do the chorionic villi appear?
At the end of the second week
How do the placental villi form/
Primary villus –> secondary villus –> tertiary villus
What kinds of villi make up the outer placenta?
Chorion lavae and chorion frondosum
What is the final form of the placenta made up of?
Decidual plate (maternal portion) and chorion frondosum (fetal portion)
What does the placenta regress to form?
Discoid placenta (16 weeks)
Where should placenta be at 38 weeks?
At top of uterus otherwise it causes huge haemorrhage
Name 3 placental complications.
- Low lying placenta
- Retained placenta
- Placental abruption (premature separation of the placenta from the uterus)
What are the main functions of the placenta?
Respiratory organ
Nutrient transfer
Excretion of fetal waste products
Hormone synthesis
What are the 2 stages of the formation of the maternal circulation?
- Differentiation of endometrium into decidua
2. Transformation of uterine spiral arteries
What is the function of the uterine NK cells?
Alter structure of spiral arteries/ open them
What happens if the opening of the spiral arteries fails?
Fetal growth restriction
or pre-eclampsia
What happens if the spiral arteries open too early?
Implantation failure
Miscarriage
(also oxidative stress causing congenital malformations)
At what point in pregnancy does the placenta not undergo any more anatomical changes?
End of 4th month
What is the difference between monozygotic and dizygotic twins?
Monozygotic - one egg, identical
Dizygotic - two eggs, non-identical
What are the types of monozygotic twinning?
- Dichorionic (2 placentas) - cleavage before implantation
- Monochorionic, diamniotic - cleavage day 6-8
- Monoamniotic - cleavage after day 8
How do conjoined twins arise?
Cleavage during embryogenesis (rare)
What increases the chances of monozygotic twins occurring?
Assisted conception like IVF
Are dizygotic twins mono or di chorionic?
All dichorionic
What are risk factors for having twins?
Age over 35 - FSH rises with age and causes double ovulation Family history Previous multiple birth Black ethnicity Increased BMI Smoking Pill
What is a sacrococcygeal teratoma?
Remnant of the primitive streak
Can take large blood supply and cause fetal heart faiulre
What switch in the placental circulation occurs at 12 weeks?
Switch from histiotrophic nutrition to haemotrophic nutrition (large rise in intraplacental oxygen)
What is the job of the two umbilical arteries?
Carry deoxygenated blood from fetus to placenta
What is the job of the umbilical vein?
Carries oxygenated blood from placenta to fetus
What is special about the umbilical vein?
ONLY time a vein carries oxygenated blood
How are the cells of the synctiotrophoblast specialised?
Brush border
Lots of mitochondria
Why is the fetal pO2 always low?
Protect from oxidative stress and enable easy transfer of oxygen from mother to baby
What is a common cause of fetal growth restriction?
Defects in amino acid transporters across the placenta
What regulates the growth and development of the alimentary tract?
Gastrin, motion and somatostatin are ingested by the fetus
When does the fetus start making insulin?
9 weeks
Why do all pregnant women become a bit diabetic?
Increase in their blood glucose to help transfer of glucose to the baby
What is gestational diabetes?
Diabetes during pregnancy - more common in pre-diabetic women
What is macrosomia?
When the baby is overweight at birth (associated with maternal obesity and diabetes)
What are the complications of macrosomia?
Labour issues
Increased risk of still birth
C section often needed
How is fluid balance maintained in the fetus?
Mostly by the placenta
Fetus also has a functional kidney that makes dilute urine (ADH is immature)
What is Oligohydramnios?
Too little amniotic fluid
What is Polyhydramnios?
Too much amniotic fluid
What is amniotic fluid made up of?
Urine Amniotic membrane secretions Fetal lung secretions Salivary secretions Fetal epithelial cells
How is fetal heart rate mainly controlled?
Through the autonomic nervous system (parasympathetic/ vagal tone dominates)
What are 4 adaptations of the fetal circulation seeing as it does not go to the lungs?
- Umbilical vein/arteries
- Ductus venosus (blood bypasses liver)
- Foramen ovale (blood from R heart to L heart)
- Ductus arteriosus
What is the fetal response to hypoxia?
Heart rate falls More resistance in umbilical artery Less resistance to middle cerebral artery Increased blood flow to heart Decreased blood flow to kidneys
What causes the foramen ovale and ductus arteriosus to close?
At delivery, cord occlusion decreases right atrial pressure
Inspiration causes vasodilation of pulmonary artery
Increased arterial pO2
Which molecules delay ductus arteriosus closure?
Prostaglandin and prostacyclin
What drugs accelerate closure of the ductus arteriosus?
NSAIDs
How are the fetus’ lungs cleared of their liquid?
- Physical force during labour
- Activation of ENaC channels
- Transpulmonary hydrostatic pressure gradient
What do some babies need to help them take their first breath?
Cold shock
When does pulmonary surfactant start to be secreted?
30 weeks
What is given to a woman with a pre-term baby to stimulate surfactant production?
Glucocorticoid
and give baby artificial surfactant when born
What can happen if a baby is not treated to stimulate surfactant production if premature?
Neonatal respiratory distress syndrome
What is the function of pulmonary surfactant?
Reduces surface tension
Increases lung compliance
Stabilises the lung
What occurs late in pregnancy to stimulate surfactant production?
Surge in cortisol
When does the switch from HbF to HbA begin?
28 weeks
What happens to plasma volume during pregnancy?
Increases
–> RAAS increases
What happens to red cell mass during pregnancy?
Increases
- being anaemic is v bad
What happens to the haematocrit during pregnancy?
Decreases
- plasma volume goes up more than red cell volume (diluted)
Why is physiological anaemia normal during pregnancy?
Plasma volume increases more than red cell volume
Why is folate important in pregnancy?
Important in DNA methylation and synthesis
Needed in early pregnancy to reduce neural tube defects
What are the 3 sources of steroids in pregnancy?
Placenta
Fetus
Mother
Where is progesterone produced during pregnancy?
By corpus luteum then placenta
What effects does progesterone have on fetal antigen responses and tidal volume?
Decreased response to fetal antigens
Increased tidal volume
What does human placental lactogen do?
Important for maternal lipolysis and anti-insulin action
What does leptin do in pregnancy?
Women become leptin restistant
Stimulates placental amino acid/fatty acid transport
Are LH and FSH detectable during pregnancy?
No
What effect does pregnancy have on BP?
Decreases in first 2 trimesters
Increases at end of pregnancy
What happens to CO and O2 consumption in pregnancy?
Increase
What happens to peripheral resistance in pregnancy?
Decreases due to increased NO synthesis etc
What happens to the mother’s kidneys during pregnancy?
GFR increases by 40-65%
Urination freq increases and urinary statis causes UTIs
Why are C section babies more likely to become obese?
Do not pick up vaginal microbiome during delivery
What feature of breathing is unchanged by pregnancy?
Respiratory rate
Do pregnant women have an acidosis or alkalosis?
Respiratory alkalosis
Low pCo2, low bicarb
What is the relationship between pregnancy and DVT?
DVT more likely due to low grade increase in coagulability
should go on heparin if high risk
What happens to the GI tract during pregnancy?
Smooth muscle relaxes
So constipation
When should morning sickness due to hCG beta stop?
15 weeks
What is the main danger to maternal health during pregnancy?
Pregnancy symptoms can mask pathology
What is the biggest cause of maternal mortality?
Cardiac problems
What are the current antenatal screening policies in the UK?
Haemoglobinopathy Infectious diseases Chromosomal abnormalities Fetal anomalies Pre-eclampsia
What are downsides to screening?
False positives
Harm from screening
Cost
What are important disease characteristics for screening?
Important health problem
Recognisable early phase
Treatment exists
How are pregnant women screened for sickle cell?
Only high risk women screened
Can offer CVS/amniocentesis
How are pregnant women screened for thalassemia?
All women screened at 10 weeks by blood test
Which infectious diseases are screened for?
HIV
Hep B
Syphilis
How are chromosomal abnormalities screened for?
Combined test in 1st trimester
What is the fetal anomaly scan?
20 week scan done by US
What are the 3 stages of fetal growth?
- Hyperplasia
- Hyperplasia and hypertrophy
- Hypertrophy
Which trimester does most fetal weight gain occur?
Third
How is fetal growth measured?
Crown-rump length (CRL)
What is the first scan for at 12 weeks?
Viability
Single/multiple pregnancy
Crown rump length (dates the pregnancy)
What is the second scan fro at 20 weeks?
Routine anomaly scan
Assessing fetal growth
Fetal anomalies
Location of placenta
How is fetal growth assessed?
Head circumference
Bi-parietal diameter
Abdominal circumference
Femur length (gives estimated fetal weight)
What is the symphysial fundal height? (SFH)
Measure of bump using a tape measure
Gives gestational age plus or minus 2cm
What should the SFH be at 20 weeks?
Umbilicus
What is the amniotic fluid index? (AFI)
Amount of amniotic fluid on US (8-18 is normal)
What is fetal growth restriction?
Placenta may not be working properly/problem with mother
Pathological
Increases risk of perinatal complications (unlike SGA babies)
How can the chances of stillbirth be reduced?
- Reduce smoking in pregnancy
- Risk assessment for FGR
- Raise awareness of reduced fetal movement
- Effective fetal monitoring during labour
What does low levels of PAPP-A at 1st trimester combined screen indicate?
Poor placentation
- increased risk of SGA/pre-eclampsia
Give aspirin
What are maternal risk factors for SGA?
Diabetes
Hypertension
Active lupus
Sickle cell disease
What are fetal risk factors for SGA?
Multiple pregnancies
Fetal structural/chromosomal abnormality
Fetal infection
Are monochorionic or dichorionic twins more high risk?
Monochorionic - should be scanned every 2 weeks
How is LGA/macrosomia defined?
Birth weight greater than 4kg
What are risk factors for LGA?
Large parents, esp mother BMI
Previous LGA baby
Diabetes
What are complications of an LGA birth?
Shoulder dystocia
Perineal trauma/PPH in mother
What is different about first aid of a pregnant women post 20 weeks?
If collapsed sit her up
Take baby out if mother has cardiac arrest (helps resuscitation of mum)
Which scan is not advised during pregnancy?
Abdominal/lumbar sacral spine X ray
