Obstetrics Antepartum Care Flashcards
Define gravidity
How many times a woman has been pregnant (regardless of outcome)
Define parity
How many babies a woman has delivered at 24+ weeks gestation
a = alive or still birth b = losses before 24 weeks parity = a + b
Define primigravid
First ever pregnancy
Define nulliparous
Has had no delivery of a baby >24 weeks gestation
Define multiparous
Has had one of more deliveries of babies >24 weeks
How is pregnancy dated in relation to conception?
Conception is 2 weeks after 1st day of LMP with a regular 28 day cycle
How are the three trimesters split?
1st trimester = 1-12 weeks
2nd trimester = 13-27 weeks
3rd trimester = 28 weeks - delivery
What is the puerperium period?
Delivery and the following 6 weeks
reversal of the physiological changes in pregnancy
How is EDD calculated based on LMP?
Add 9 months + 7 days to 1st day of LMP
Pregnancy lasts 38 weeks from conception/40wks from 1st dat LMP
How is a pregnancy dated during:
6-12 weeks
14-20 weeks
6-12 weeks = crown-rump length
14-20 weeks = biparietal diameter (BPD)
A woman who books in for the first time in 3rd trimester needs two growth scans two weeks apart
What the 1st antenatal (booking) visit?
When is it done?
A pregnant patient is seen by a midwife, risk assessment, decided if it is midwife/GP care vs consultant lead care
Book by 12 weeks (or within 2 weeks if >12wk gestation)
What are the first antenatal bloods done at a booking visit? (6)
Routine:
1) FBC - check for anaemia (<110g/l)
2) Haemoglobinopathies
- sickle cell anaemia
- thalassaemia
3) Rhesus status and Ab
4) Blood group
Infection screen:
5) HIV (opt out test)
- mothers need to be on anti-retrovirals to ensure load undetectable at 36 weeks
- baby has medication for 4 weeks after to reduce HIV risk to 1%
6) Hep B
- receive vaccination at birth if born to +ve mother
7) Syphilis
- mother needs to have received full treatment 4 weeks priorate delivery otherwise baby has to have IV treatment
What health advice is given at a booking visit?
Diet eg avoid unpasteurised products like soft cheese / fish high in mercury like swordfish Smoking cessation Alcohol Folic acid - ideally preconceptual Vit D
When can an US detect a pregnancy?
Approx 5wk gestation
When are early pregnancy scans and what can they determine?
<11wk
Location, viability and dating of pregnancy
List some indications for an early pregnancy scan
Bleeding, pain or hyperemesis gravid (to exclude a molar pregnancy)
What antenatal visits are routine for a healthy pregnant woman who is nulliparous?
10 antenatal visits
Booking (8-10 weeks) then: 16, 25, 28, 31, 34, 36, 38, 40, 41
What antenatal visits are routine for a healthy pregnant woman who is multiparous?
8 antenatal visits
Booking (8-10 weeks) then: 16, 28, 34, 36, 38, 40, 41
When are foetal movements usually felt?
“Quickening” = 16-25 weeks
In first pregnancy this can be closer to 25 weeks, by the second can be as early as 13 weeks
Outline visits:
28, 34, 36, 40, 41 weeks
28: Hv and Rh antibodies (anti-D if needed)
34: discuss labour, birth and pain relief
36: discuss breast-feeding, neonatal vit k, postnatal care, postnatal depression
40: discuss post-dates pregnancy
41: offer membrane sweep and book IOL by 42wk
When is the Combined Test and what does it measure?
11+0 to 13+6 weeks (scan and blood test)
US (nuchal) scan measurement of subcutaneous tissue between the skin and soft tissue of overlying cervical spine with fetus in neutral position
Maternal bloods
- hCG
- PAPP-A
Get early result
What is the detection rate of the Combined Test and what three syndromes does it test for?
Detection rate 85%
Test for trisomy’s:
Down’s syndrome (Chr 21)
Edwards syndrome (Chr 18)
Pautaus syndrome (Chr 13)
How sensitive is the combined test?
85%
When is the Quadruple Test and what does it measure?
For women who book later in pregnancy - between 15+0 and 20+0. Uses a dating scan (not NT scan) and maternal bloods:
Maternal bloods:
- AFP
- hCG
- Oestriol
- Inhibin-A
What is the significance of a raised serum AFP (Alpha fetoprotein)?
AFP prduced by fetal liver, elevated in open NTD, exomphalos, teratomas, Turner’s syndrome
What is pregnancy-associated plasma protein A (PAPP-A)?
A large glycoprotein produced by placenta involved in matrix materialisation and angiogenesis
- Low levels = poor early placentation
- Low levels in 1st trimester screening associated with trisomies 18 and 21, pre-eclampsia, growth restriction and preterm delivery
What is the integrated test?
A better screening test than the combined test but is expensive and rarely used. Involves:
- NT + PAPP-A in first trimester
- Quadruple test in 2nd trimester
What are screen positive women?
Risk of 1 in 150 or more is regarded as ‘positive’
Offer invasive screening - CVS or amniocentesis
What is an ‘anomaly’ scan and when is it taken?
A detailed USS taken at 20 weeks aiming to identify specific structural malformations
What is Non-invasive Pre-natal Testing (NIPT) and when is it done?
Detects free-fetal DNA in maternal circulation
- Only available privately (but being rolled out in NHS)
From 10 weeks onwards
How sensitive is NIPT? Is it diagnostic?
99% sensitive for Down’s
97% sensitive for Edward’s
NOT DIAGNOSTIC - would still need CVS/amniocentesis if result came back high risk for diagnosis
What 7 features are assessed checking for fetal normality at an anomaly scan?
1) Head shape and internal structures
- Cavum pellucidum
- Cerebellum
- Ventricullar size at atrium <10mm
2) Spine
- Longitudinal and transverse views
3) Renal pelvis
- <5mm AP measurement
4) Abdominal shape and content at level of:
- Stomach
- Kidneys
- Umbilicus
5) Thorax at level of cardiac ‘four chamber’ view
6) Arms
- 3 bones and hand
7) Legs
- 3 bones and foot
What are two further features shown on an optimal standard 20wk anomaly scan?
Cardiac outflow tracts
Face and lips
What CNS abnormalities may be detected at an anomaly scan? (3)
CNS = 76%
- NTD
- Anencephaly = absence of skull vault and cerebral context (incompatible with life)
- Spina bifida = incomplete fusion of vertebrae potentially allowing herniation of all or part of the spinal cord
What urinary tract abnormalities may be detected at an anomaly scan? (3)
Urinary tract = 67%
- Renal agenesis = bilateral is lethal (Potter’s syndrome) as anhydraminos causes lung hypoplasia. Without kidneys, fetus cannot produce urine needed to make amniotic fluid
- Posterior urethral valve syndrome = occurs in male foetuses where folds of mucosa block bladder neck causing outflow obstruction (back pressure may cause irreversilble renal damage and oligohydraminos)
- Hydronephritis = 75% of all renal abnormalities. Half resolve spontaneously in neonatal period (usually due to pelviueretruc obstruction, vesicoureteric reflux, uterocele, or posterior urethral valves)
What pulmonary abnormalities may be detected at an anomaly scan? (3)
Pulmonary = 50%
- Lung hypoplasia = failure to develop sufficient alveoli to permit adequate gas exchange at delivery (mortality 71-95%)
- Diaphragmatic hernia = a defect in diaphragm leading to abdo contents herniating into chest (30% incidence of aneuploidy and strongly associated with other malformations)
- Congenital cystic adenomatoid malformation CCAM = rare lung disease where normal alveolar tissue replaced by proliferation of cysts resembling bronchioles
What GI abnormalities may be detected at an anomaly scan? (3)
GI = 42%
- Exomphalous (omphalocele) = failure of the gut to return into the abdo cavity after normal embryological extrusion and rotation. The bowel and sometimes other viscera are contained within a sac and umbilical cord arises from apex of sac (1/3rd with chromosomal abnormalities and 50% have other malformations)
- Gastroschisis = protrusion of gut through an anterior abdo wall defect, usually to risk of umbilical cord, the bowel is not covered by a sac and floats freely (unlike exomphalous were they are covered by a membrane)
- GI obstruction:
1) Duodenal atresia = 30% have trisomy 21
2) Oesophageal atresia = 15% have aneuploidy
Other atresia may occur with syndromes of gastroschisis
CF common with bowel obstruction
What is the most common cardiac abnormality spotted on an anomaly scan?
- Ventricular septal defects most common
- May be associated with trisomy 21, 18 or other congenital abnormalities
NB 24% skeletal abnormalities detected on anomaly scan
What is chorionic villus sampling (CVS) and when is it performed?
Performed between 10-13 weeks
Aspiration of small amount of cells analysed using FISH and PCR. US guidance either transabdominally or transcervically
What are some indications for CVS?
- For karyotyping if 1st trimester screening test suggests high risk for aneuploidy
- For DNA analysis if parents are carriers of identifiable gene mutation eg CF or thalassaemia
What are some benefits of CVS?
- Allows 1st trimester TOP if an abnormality is detected (surgical/medical and before pregnancy is physically apparent)
- Rapid karyotyping as trophoblast cells are more easily cultured than squames from amniocentesis
What are some risks of CVS?
- Miscarriage approx 1%
- Higher risk of vertical transmission of blood borne viruses such as HIV / Hep B
- Rarely false -ve results from contamination with maternal cells
- Placental mosaicism producing misleading results (estimated <1%)
What is amniocentesis and when is it performed?
Aspiration of amniotic fluid which contains petal cells shed from the skin and gut using a fine gauge needle under US guidance transabdominally
Usually 15 weeks onwards
What can be prenatally diagnosed using amniocentesis?
- Infections such as CMV and toxoplasmosis
- Inherited disorders suck as sickle cell anaemia, thalassaemia and CF
- Chromosomal abnormalities eg trisomy 21
What are the indications of amniocentesis?
- Karyotyping if screening tests suggest aneuploidy
- For DNA analysis if parents are carriers of identifiable gene mutation eg CF or thalassaemia
- For enzyme assays looking for inborn errors of metabolism
- For diagnosis of fatal infections such as CMV and toxoplasmosis
What are the benefits of amniocentesis?
- Lower procedure attributed miscarriage rate than CVS (approx 1%)
- Less risk of maternal contamination or placental mosaicism
What are the risks of amniocentesis?
- Miscarriage as a result of amniocentesis at approx 1%
- Failure to culture cells approx 0.5%
- Full karyotyping may take 3 weeks
How are blood groups classified?
ABO and rhesus genotype
What does the Rhesus system consist of?
Three linked gene pairs - one allele of each pair is dominant to the other
= C/c, D/d, E/e
- The D gene is the most significant cause of isoimmunisation
(Other significant antigens include c, E and atypical Kell antibody)
NB - There are only 5 antigens as d is not an antigen, it merely implies the absence of D (thus their immune system will recognise the D antigen as foreign if exposed to it)
What is the genetic inheritance of Rh blood groups?
Mendelian inheritance
What is the pathophysiology of rhesus disease
Fetal cells cross into maternal circulation in normal pregnancy (increased in ‘sensitising events’). The fetus may carry the gene for an antigen which the mother does not have.
With rhesus disease:
1) Fetus may be D/d (rhesus D +ve) whilst mother is d/d (rhesus D -ve)
2) Individuals exposed to foreign antigen mount an immune response (sensitisation); initially this is IgM which cannot cross placenta so pregnancy is not at risk
3) Re-exposure in subsequent pregnancy causes primed memory B cells to produce IgG which can actively cross into fetal circulation
4) IgG binds to fetal red cells which are then destroyed in reticuloendothelial system
5) This causes haemolytic anaemia = if erythropoiesis is inadequate to compensate, severe anaemia causes high output cardiac failure, ‘fatal hydrops’ and death
- In milder cases, haemolysis leads to neonatal anaemia or jaundice due to increased bilirubin levels
List potential sensitising events for rhesus disease
- TOP or evacuation of retained products of conception (ERPC) after miscarriage
- Ectopic pregnancy
- Vaginal bleeding >12 wks or earlier if heavy
- External cephalic version (ECV)
- Blunt abdominal trauma
- Invasive uterine procedure eg amniocentesis or CVS
- Intrauterine death
- Delivery
= anything that causes mixing of maternal and fatal blood
What is immune hydrops fetalis?
Rhesus isoimmunisation = severe complication of rhesus incompatibility
How common is rhesus disease in each trimester?
Common - tends to decrease as pregnancy advances
1st trimester = 39%
2nd trimester = 30%
3rd trimester = 20%
What is the management of rhesus disease?
All women should be checked for antibodies (rhesus and atypical) at booking, 28 weeks and 24 weeks
- If antibodies are detected, identifying partner’s status will help determine potential fatal blood group and risk to the fetus
- PCR of fetal cells in maternal blood may also determine fetus’s blood group, if the parter is heterozygous or the paternity is uncertain
- +ve but low levels of antibodies (<10IU/mL) should prompt repeat testing every 4 weeks
What is the management of maternal antibodies detected <10IU/mL and >10IU/mL
- +ve antibodies but <10UI/mL = repeat testing every 4 weeks
- > 10UI/mL = assessment for fetal anaemia
NB - The peak systolic velocity of the fetal middle cerebral artery (MCA) should be measured looking for indication of anaemia
What can be measured to check for fetal anaemia?
The peak velocity of the fetal middle cerebral artery (MCA) = raised indicates anaemia
What is the treatment of rhesus disease?
If fetal haematocrit <30: transfusion of packed red cells into umbilical vein at cord insertion or into hepatic vein.
Performed from 18wk onwards every 2 weeks or until MCA becomes normal
What are post-natal features of rhesus disease?
- Anaemia (corrected by blood transfusion)
- Severe anaemia may be accompanied by coagulopathy from decreased platelets and clotting factors
- Hyperbilirubinaemia and jaundice occur as immature neonatal liver unable to clear breakdown products of RBC breakdown
- Antibodies can persist for weeks causing haemolysis in neonates, requires close monitoring with haematocrit measurements
What is the prevention of rhesus disease?
- Mother given sufficient anti-D Ig to bind to any fetal red cells in her circulation carrying the D antigen = prevents her own immune system from recognising them and becoming sensitised
What is the routine treatment of anti-D for rhesus -ve women?
Anti-D (500 IU) given to all women who are rhesus -ve (d/d):
- Routinely at 28 and 34 weeks
- Within 72hrs of any potentially sensitising event
- After delivery if neonate is found to be rhesus +ve (D/d)
What is the Kleihauer test?
Done if a large feto-maternal haemorrhage is suspected where the standard dose of anti-D is not sufficient. It assesses the number of fetal cells in maternal circulation postnatally to see if larger anti-D doses are required to mop up fetal D antigen containing cells.
NB - other antibodies such as anti-kell and anti-c now account for half the cases of fetal haemolysis
How common is rhesus disease? Name two factors which have caused this
Extremely rare (85% pop are Rh+ve), and only 2% of RhD-ve women in UK become sensitised
- Use of anti-D
- Smaller family sizes
What factors are considered on a customised growth chart?
Maternal ethnicity, weight, height and parity
What do doppler US measure? What population are they useful in?
Measure blood flow in uterus, placenta and fetus
= useful in high risk pregnancies
What is Pulsatility index? What if there is an increased umbilical artery PI vs MCA?
PI = indicator of resistance
If increased in umbilical artery and decreased in MCA = blood being redirected to brain
What is the Umbilical Artery Doppler?
Measures resistance in placenta
- High resistance = placental failure (higher risk of intrauterine death)
- If very pre-term (<28wk) can be used to time delivery
ie if absent or reversed, consider CS
What is the Uterine Artery Doppler?
Measures resistance within the placenta
- Usually carried out at 23 wks
- High resistance = increases risk of maternal pre-eclampsia and fetal growth restriction (requires increased fetal monitoring)
When are fetal growth scans and how frequently?
When there are increased risk of growth abnormalities eg previous growth restriction, pre-eclampsia, measuring small for dates
Scans should be at least 2 weeks apart
What should be done if a fetal growth scan shows a SGA baby?
Umbilical artery doppler to distinguish between a fetus who is small and coping from those who are beginning to decompensated and require early delivery
What is measured in a growth/fetal wellbeing scan?
- Biparietal diamete (BPD)
- Head circumference (HC)
- Abdo circumference (AC)
- Femur length (FL)
- Liquor volume
