Obstetrics: Antenatal Care- Fetal Abnormalities Flashcards
What do we mean by the following:
- Lie
- Presentation
- Position
- Lie: relationship between long axis of fetus and the mother. Can be longitudinal, transverse or oblique
- Presentation: fetal part that first enters pelvis. Can be cephalic vertex (safest, most common), breech, shoulder, face
- Position: position of fetal head as it exits birth canal. Can be occipito-anterior (most common), occipito-posterior, occipito-transverse
State some risk factors for abnormal lie
- Multiple pregnancy
- Uterine abnormalities e.g. fibroids
- Placenta praevia
- Primiparity
- Prematurity (remember most breech resolve later in pregnancy)
What investigation should be done if you suspect abnormal lie?
Ultrasound scan
90% of malpositions spontaneously rotate to occipito-anterior as labour progresses; true or false?
True (if not, rotation & instrumental delivery can be done- or caesarean)
What do we mean by breech presentation?
How common is it?
- Presenting part of fetus is the buttocks or feet (rather than head as in cephalic presentation)
- ~20% breech at 28 weeks but then <5% by 37 weeks
Most breech presentations seem to be chance occurrences; true or false?
True
There are 4 types of breech presentation; define the following:
- Complete breech
- Incomplete breech
- Extended breech
- Footling breech
- Complete breech: the legs are fully flexed at the hips and knees
- Incomplete breech: one leg flexed at the hip and extended at the knee
- Extended breech (frank breech): both legs flexed at the hip and extended at the knee
- Footling breech: one or both legs extended at hit so that foot is the presenting part
Most sources say there are 3 main types: complete, extended/frank & footling
Babies that are breech before 36 weeks often turn spontaneously; true or false?
True
How is breech presentation usually diagnosed?
Clinical examination (round head can be felt in upper part of uterus and irregular mass of fetal buttock & legs in pelvis)
Fetal heart may be auscultated higher
Discuss the management of breech presentation
If not turned by 36 weeks, options include:
- External cephalic version (ECV)
- If ECV fails, two options:
- Vaginal delivery with experienced midwifes with access to emergency theatres if required (~40% chance requiring caesarean)
- Elective caesarean section
- However, if first baby in a twin pregnancy is breech caesarean section IS required
RCOG say ‘Women should be informed that planned caesarean section carries a reduced perinatal mortality and early neonatal morbidity for babies with a breech presentation at term compared with planned vaginal birth’ hence caesarean section is recommended
For external cephalic version (ECV), discuss:
- What it is
- Who/when it can be used
- Success rate
- Technique used to attempt to turn fetus from breech position into cephalic position using pressure on abdomen
- ECV can be used:
- After 36 weeks for nulliparous women
- After 37 weeks for women who have given birth previously
- ~50%
What is required before ECV and why?
What is required within 72hrs of ECV?
- Tocolysis with SC terbutaline to relax uterus before ECV making it easier to turn baby
- Rhesus-D negative women require anti-D prophylaxis within 72hrs (including Kleihauer test to determine dose of anti-D required)
State some potential complications of ECV
- Transient fetal heart abnormalities
- Placental abruption
- Failure
What is the major potential complication of a breech presentation?
Cord prolapse
Others include:
- Fetal head entrapment
- Premature rupture membranes
- Birth asphyxia
- Intracranial haemorrhage
Define stillbirth
Birth of a dead fetus after 24 weeks gestation as a result of intrauterine fetal death (IUFD)
Occurs in ~1 in 200 pregnancies
State some risk factors for stillbirth
- Fetal growth restriction
- Smoking
- Alcohol
- Increased maternal age
- Maternal obesity
- Twins
- Sleeping on the back (as opposed to either side)
State some potential causes of stillbirth
- Unexplained (around 50%)
- Pre-eclampsia
- Placental abruption
- Vasa praevia
- Cord prolapse or wrapped around the fetal neck
- Obstetric cholestasis
- Diabetes
- Thyroid disease
- Infections, such as rubella, parvovirus and listeria
- Genetic abnormalities or congenital malformations
***HOWEVER, unexplained stillbirth is still common
What are 3 key symptoms to always check when taking history from pregnant woman?
- Fetal movements?
- Abdominal pain?
- Vaginal bleeding?
Prevention of stillbirth involves screening for and treating- where possible- any conditions that can cause stillbirth. All pregnant women have a risk assessment for having a baby that is small for gestational age (SGA) or with fetal growth restriction (FGR). What do those at risk have?
- Serial growth scans
- May need planned early delivery when growth is static or other concerns
What is the investigation of choice for diagnosing intrauterine fetal death (IUFD)?
Ultrasound to visualise fetal heartbeat
Passive fetal movements are possible after IUFD; true or false?
True (repeat scan can be offered to confirm situation)
Discuss the management of IUFD
-
First line= vaginal birth
- Induction of labour
- Or expectant management (if immediate delivery not required. Need close monitoring)
- Anti-D prophylaxis in rhesus negative women & Kleihauer test to determine dose
- Dopamine agonists (e.g. cabergoline) can be used to supress lactation after stillbirth
- With parental consent testing is carried out to determine cause
- Support following delivery:
- Counselling
- Support with wishes such as seeing baby, naming baby, photographs
- Support with funeral arrangements
Following IUFD and stillbirth, testing is carried out- with parental consent- to try and determine underlying cause; what may be involved in such testing?
- Genetic testing of the fetus and placenta
- Postmortem examination of the fetus (including xrays)
- Testing for maternal and fetal infection
- Testing the mother for conditions associated with stillbirth, such as diabetes, thyroid disease and thrombophilia
Define the following:
- Low birth weight
- Small for gestational age (SGA)
- Severe SGA
- Fetal SGA
- Severe fetal SGA
- Low birth weight= birth weight <2500g
- SGA= infant with birth weight <10th centile for it’s gestational age
- Severe SGA= infant with birth weight <3rd centile for it’s gestational age
- Fetal SGA= fetus with estimated fetal weight (EFW) or abdominal circumference (AC) <10th centile for it’s gestational age
- Severe fetal SGA= fetus with estimated fetal weight (EFW) or abdominal circumference (AC) <3rd centile for it’s gestational age
SGA is assessed based on two ultrasound measurements; sates these
Measurements taken on ultrasound:
- Estimated fetal weight (EFW)
- Fetal abdominal circumference (AC)
Customised growth charts are used to assess the size of the fetus, based on the mother’s:
- Ethnic group
- Weight
- Height
- Parity
Causes of SGA can be divided into two main categories; one of these categories can be further subdivided into two further categories. Outline the categorisation of SGA
- Constitutionally small
- Fetal growth restriction (GFR)/intrauterine growth restriction (IUGR)
- Placenta mediated growth restriction
- Non-placenta mediated growth restriction
Define the following:
- Constitutionally small
- Fetal growth restriction (FGD)/intrauterine growth restriction (IUGR)
- Placenta mediated growth restriction
- Non-placenta mediated growth restriction
- Constitutionally small: small size at all stages but following centiles; matching mother & others in family
- Fetal growth restriction (FGD)/intrauterine growth restriction (IUGR): fetus is small or not growing as expected due to pathology
- Placenta mediated growth restriction: fetus is small or not growing as expected due to pathology affecting the transfer of nutrients via the placenta. Growth often normal initially then slows.
- Non-placenta mediated growth restriction: fetus is small or not growing as expected due to fetal pathology e.g. chromosomal abnormality, issues with metabolism, fetal infection
Why may the ratio of head circumference to abdominal circumference be significant when assessing whether a fetus is small for gestational age?
The ratio of head circumference (HC) and AC may be significant; a symmetrically small fetus is more likely to be constitutionally small whilst an asymmetrically small fetus is more likely to be caused by placental insufficiency. The ‘brain-sparing’ effect can be identified by abnormal doppler studies.
State some causes of placenta mediated growth restriction
- Idiopathic
- Pre-eclampsia
- Maternal smoking
- Maternal alcohol
- Anaemia
- Malnutrition
- Infection
- Maternal health conditions
State some causes of non-placenta mediated growth restriction
- Genetic abnormalities
- Structural abnormalities
- Fetal infection
- Errors of metabolism
Other than being below 10th centile, there may be other signs of fetal growth restriction; state some of these
- Reduced amniotic fluid volume (placental insufficiency can impair fetal kidney function)
- Abnormal Doppler studies
- Reduced fetal movements
- Abnormal CTGs
State some minor and major risk factors for SGA
Discuss the monitoring required for SGA
Low risk women
- Have symphysis fundal height (SFH) measured at every antenatal appointment from 24 weeks onwards to identify possible SGA
- This is plotted on customised growth chart to assess appropriate size for individual woman
- If SFH <10th centile → book for serial growth scans with umbilical artery doppler
Women with risk factors or issues measuring SFH
- ≥ 3 minor risk factors:
- Reassess at 20 weeks
- If still ≥ 3, arrange uterine artery doppler
- If normal, reassess in 3rd trimester
- If abnormal, serial growth scans and umbilical artery doppler
- ≥1 major risk factor:
- Reassess at 20 weeks
- If still ≥ 1, serial growth scans and umbilical artery doppler
Issues with monitoring SFH e.g. large fibroids,, BMI >35
- Serial growth scans & umbilical artery doppler
- ***NOTE:* The local guidelines for the initiation and frequency of ultrasound scans may vary. An example regime is a growth scan every four weeks from 28 weeks gestation. Ultrasound frequency is increased where there is reduced growth velocity or problems with umbilical flow.
What do ultrasounds, monitoring for SGA, measure?
- Estimated fetal weight (EFW) (determine the growth velocity)
- Abdominal circumference (AC) (determine the growth velocity)
- Umbilical arterial pulsatility index (UA-PI) (measure flow through the umbilical artery)
- Amniotic fluid volume
How do you measure symphysis fundal height?
What are
Measuring SFH
- Ensure bladder empty
- Ensure woman comfortable in semi-recumbent position
- Measure from fundus to top of pubis symphysis
Expected measurements (see image)
Discuss the management of SGA
- Identifying those at risk of SGA and monitoring with UAD +/- serial growth scans
- Treating modifiable risk factors e.g. stop smoking, weight loss
- Aspirin given to those with SGA from 16 weeks onwards
- Aspirin to those at risk of pre-eclampsia
- If fetus identified as SGA, investigating to find underlying cause:
- BP & urine dipstick: pre-eclampsia
- Uterine artery doppler scanning
- Detailed fetal anomaly scan by fetal medicine
- Karyotyping for chromosomal abnormalities
- Testing for infections (e.g. CMV, toxoplasmosis, syphilis)
-
Early delivery considered if growth static or other problems identified
- *Remember, give corticosteroids if delivery between 24 - 35+6 planned
State some potential short term complications of FGR/IUGR
- Fetal death or stillbirth
- Birth asphyxia
- Neonatal hypothermia
- Neonatal hypoglycaemia
- Neonatal polycythaemia
- Usual complications of being premature if premature delivery
State some potential long term complications of FGR/IUGR
- Cardiovascular disease, particularly hypertension
- Type 2 diabetes
- Obesity
- Mood and behavioural problems
- Malignancy (breast, ovarian, colon, lung, blood)
Why may the ratio of head circumference to abdominal circumference be significant when assessing whether a fetus is small for gestational age?
The ratio of head circumference (HC) and AC may be significant; a symmetrically small fetus is more likely to be constitutionally small whilst an asymmetrically small fetus is more likely to be caused by placental insufficiency. The ‘brain-sparing’ effect can be identified by abnormal doppler studies.
Define the following:
- Large for gestational age
- Fetal large for gestational age
- Large for gestational age: birthweight >4500g
- Fetal large for gestational age: estimated fetal weight >90th centile
State some potential causes of macrosomia
- Constitutional
- Maternal diabetes
- Previous macrosomia
- Maternal obesity or rapid weight gain
- Overdue
- Male baby
Most women with large for gestational age pregnancy will have a successful vaginal delivery; true or false?
True, NICE guidelines (2008) advise against induction of labour only on the grounds of macrosomia.
What investigations are done when there is a large for gestational age fetus?
At every antenatal appointment after 24 weeks, will measure SFH; if this is greater than expected on ≥2 occasions or rapid growth on one occasion should be offered:
- Ultrasound: estimate fetal weight and exclude polyhydramnios
- May then do oral glucose tolerance test: test for gestational diabetes
State some potential maternal complications associated with large for gestational age
- Shoulder dystocia
- Failure to progress
- Perineal tears
- Instrumental delivery or caesarean
- Postpartum haemorrhage
- Uterine rupture (rare)
Main risk with large for gestational age fetus if shoulder dystocia. Discuss how risks at delivery can be reduced
- Delivery on a consultant lead unit
- Delivery by an experienced midwife or obstetrician
- Access to an obstetrician and theatre if required
- Active management of the third stage (delivery of the placenta)
- Early decision for caesarean section if required
- Paediatrician attending the birth
Then if shoulder dystocia does occur following management for that
State some potential fetal complications associated with large for gestational age
- Birth injury (Erbs palsy, clavicular fracture, fetal distress and hypoxia)
- Neonatal hypoglycaemia
- Obesity in childhood and later life
- Type 2 diabetes in adulthood
What do we mean by oligohydramnios?
Low level of amniotic fluid
Amniotic fluid index (AFI) <5th centile for gestational age
Describe what happens to volume of amniotic fluid during pregnancy
- Increases until 33 weeks
- Plateaus 33-38 weeks
- Then declines
Volume at term is ~500mL
Remind yourself how amniotic fluid is created
- Mostly made of fetal urine output with small contributions from placenta and some fetal secretions (e.g. respiratory)
- Fetus breathes and swallows amniotic fluid
- Processed by kidneys
- Excreted as urine
- Anything that reduces production of urine, blocks urine output or a rupture of membranes can lead to olighydramnios
State some potential causes of olighydramnios
- Placental insufficiency (results in blood flow being redistributed to fetal brain ratehr than abdomen & kidneys)
- Renal agenesis (Potter’s syndrome)
- Non-functioning kidneys e.g. bilateral multicystic dysplastic kidneys
- Obstructive uropathy
- Preterm prelabour rupture membranes
- Genetic/chromosomal abnormalities
- Viral infections (but may also cause polyhydramnios)
Discuss the management of oligohydramnios
Depends on underlying cause; two most common are:
- Ruptured membranes (see separate FCs)
- Placental insufficiency (see separate FCs; involve serial growth scans, early planned delivery)
State some potential complications of oligohydramnios
- Premature delivery
- Pulmonary hypoplasia
- Muscle contractures (amniotic fluid allows fetus to move limbs in utero hence without it fetus can develop muscle contractures)
What do we mean by polyhydramnios?
Polyhydramnios refers to an abnormally large level of amniotic fluid during pregnancy.
It is defined by an amniotic fluid index that is above the 95th centile for gestational age.
State some potential causes of polyhydramnios
- Idiopathic (50-60% cases)
- Abnormal fetal swallowing (e.g. oesophageal atresia, CNS abnormalities, muscular dystrophies, congenital diaphragmatic hernia obstructing the oesophagus)
- Duodenal atresia
- Anaemia
- Fetal hydrops
- Twin-to-twin transfusion syndrome
- Increased lung secretions
- Genetic or chromosomal abnormalities
- Maternal diabetes
- Maternal ingestion of lithium (causes fetal diabetes insipidus)
- Macrosomia – larger babies produce more urine.
What investigations might you consider for polyhydramnios?
- OGTT for maternal diabetes
- TORCH test for infections (Toxoplasmosis, Other (Parvovirus), Rubella, Cytomegalovirus, Hepatitis)
- Karyotyping
Discuss the management of polyhydramnios
- No medical intervention is required in the majority of women with polyhydramnios
- If severe symptoms, amnioreduction can be considered (not routinely done)
- Indomethacin can be used to enhance water retention & reduce fetal urine output (BUT it is associated with premature closure of ductus arteriosus so not used before 32 weeks)
- In cases of idiopathic polyhydramnios, baby needs to be examined by paediatrician before first feed; NG tube is passed to check there is not an oesophageal atresia or tracheoesophageal fistula
State some potential complications of polyhydramnios
- Increased incidence preterm labour (over distension of uterus)
- Increased risk of malpresentation (fetus has more room to move around)
- Increased risk PPH (uterus has to contract further)
