Antenatal screening Flashcards
What are the principles of screening?
Highly sensitive Highly specific High positive predictive value Easily used in a large population Safe and cheap Quick and straightforward to perform Able to detect a disease with a known natural history and where early diagnosis has a proven benefit
How is sensitivity assessed?
True positive/ (positive + false negative)
How is specificity assessed?
True negative / (negative + false positive)
What eye screening is offered to diabetic women in pregnancy?
DE screen when first present for care
DE screening anually
What bloods should be taken off in the 1st trim?
Sickle cell and thalassaemia
IF WANTED; blood test for DSS
Syphilis, hep B and C, HIV and rubella susceptibility
Haemaglobin, group, rhesus and red cell antibodies
When are scans performed in pregnancy?
At booking app; 11-13 weeks
Anomaly scan at 20 weeks
What does the newborn gurthrie prick test for?
CF Congenital hypothyroidism Sickle cell Metabolic disorders: Phenylketonuria (PKU) medium-chain acyl-CoA dehydrogenase deficiency (MCADD) Maple syrup urine disease (MSUD) Isovaleric acidaemia (IVA) Glutaric aciduria type 1 (GA1) Homocystinuria (pyridoxine unresponsive) (HCU)
What is performed at the booking visit?
Hx; Menstruation Medical Obstetric Family Social Exam: BMI BP CVS Abdominal
What is the cut off for BMI in terms of allowing for midwife led care in place of obstetric lead care?
BMI of 40 needs to be under care of obstetrician
What is naegele’s rule?
Predicts an EDD based on LMP
Add on 9 months and 7 days to arrive at due date
What is the most accurate measurement of EDD?
CRL on USS
What investigations are performed at the booking visit?
Bloods; Hb ABO Rhesus Syphilis HIV Hep B and C Urinalysis; MSSU, C+S USS
What is assessed on USS at the booking visit?
Confirm viability Singleton/ multiple pregnancy Estimate gestational age Detect major structural anomalies; abdominal wall defects or anencephaly Offer DSS
Where should you look if there is an empty sac but a positive pregnancy test?
Adnexae for ectopics
Do hCG level to monitor
What are the different types of twins?
Dichorionic/ diamniotic
Monochorionic/ diamniotic
Monochorionic/ monoamniotic
Conjoined
What is assessed at follow up antenatal visits with the midwife post booking appointment?
Hx; physical and mental health, foetal movements
Exam: BP and urinalysis, symphysis (fundal height(, lie and presentation, engagement of presenting part, foetal heart auscultation
Which are the main anomalies incompatible with life?
Major heart abnormalities
Anencephaly
Trisomy 13 and 18
What is assessed in the H+N in anomaly scan?
Skull
Nunchal skin fold
Brain; cavum septum pellucidum, ventricular atrium, cerebellum
What is assessed in the face in anomaly scan?
Lips; cleft lip
What is assessed in the chest in an anomaly scan?
Heart; four chambers. outflow tracts
Lungs
What is assessed in the abdomen in an anomaly scan?
Stomach; stomach and short intra-hepatic section of umbilical vein
Abdo wall; bowel, renal pelvis
Bladder
What is assessed in the spine in an anomaly scan?
Vertebrae
Skin covering
What is assessed in the limbs in an anomaly scan?
Femur
Hands; metacarpals
Feet; metatarsals
What is assessed in the uterine cavity in an anomaly scan?
Amniotic fluid
Placenta
What are the main foetal anomalies picked up on the 20 wk scan?
Anencephaly Open spina bifida Cleft lip Diaphragmatic hernia Gastroschisis Exomphalos Serious cardiac abnormalities Bilateral renal agenesis Lethal skeletal dysplasias Edwards syndrome (trisomy 18) Patau's sundrome (trisomy 13)
What is placental praevia?
Placenta is low lying in the womb and covers all or part of the cervix
In most women, as the women grows upwards, the placenta moves with it so that it is in a normal position before birth
What should be offered if a low lying placenta is seen at the anomaly scan?
Scan at 32 weeks
If this is unclear, vaginal scan
What is the recommendation for women with placenta praevia?
C-section
How is down’s syndrome assessed in the 1st trim?
Measure of nuchal thickness; >3.5mm is bad
PAPP-A and hCG blood testing
How should a risk of down’s syndrome be estimated?
hCG (goes up)
PAPP-A (goes down)
NT
Maternal age
What is PAPP-A?
It is produced by the placental syncytiotrophoblast and deciduas. It increases the bioavailability of insulin like growth factor, which in turn mediate trophoblast invasion and modulates glucose and amino acids transport in the placenta
What down’s risk assessment can be performed in 2nd trim?
Blood sample at 15-20 wks
Assay of hCG and AFP
What is considered high risk for down’s syndrome?
> 1:250 change
Then a scan is arranged with amniocentesis
What can a thickened nuchal thickness indicate?
Chromosomal defect
Foetal death
Major foetal anomaly
Much more unlikely to have a foetus alive and well
What maternal markers are used for 2nd trim screening for aneuploidy?
AFP
hCG
Unconjugated oestradiol (UE3)
Inhibin A
When is an amnio performed?
After 15 weeks
What is the rate of miscarriage from an amniocentesis?
1%
When is chorionic villus sampling (CVS) performed?
After 12 weeks
What is the miscarriage rate for CVS?
2%
What are the 2 major hemoglobin disorders?
Sickle cell
Thalassemias
What is the rate and mode of inheritance of sickle cell and thalassemia?
AR
50% risk of carrier
25% risk affected
25% risk carry nothing
What does a normal haemoglobin contain?
Haemaglobin A:
2 alpha and 2 beta chains
What is the difference between HbS and thalassemias?
HbS; mutation results in a change to the structure and quality of hemoglobin variants
Thalassaemias; amount of hemoglobin the body produces is reduced, impacting on its oxygen carrying capacity
Risk of HbS in pregnancy?
Stroke, VTE, meningitis Miscarriage Infection Still birth Pelvic inflammation Papillary necrosis Bone crisis Amnionitis Anaemia Pulmonary cx Premature birth Hypertx Placenta praevia Maternal mortality
What are the different types of maternal anaemia?
Iron deficiency
Folate deficiency
B12 deficiency
Why is maternal Hb optimised for birth?
To prevent fatal PPH
What is foetal hydrops?
Serious condition
Abnormal accumulation of fluid in 2 or more foetal compartments:
Ascites
Pleural effusion
Pericardial effusion
Skin oedema
Can be assoc with polyhydramnios and placental oedema
What is rhesus disease?
Haemolytic disease of the newborn;
In a foetus; anaemia
In a newborn; anaemia and jaundice
How can foetal anaemia be assessed?
Doppler to assess increased flow in the middle cerebral artery; indication that the baby is hypoxic and anaemic
What rhesus of the mother puts the baby at risk?
Rhesus neg
What are RF for gestational diabetes?
BMI > 30
Previous macrosomic baby weighing 4.5kg (9 pounds 9) or above
Previous gestational diabetes
FMHc of diabetes
Minority ethnic family origin with high prevalence of diabetes
What is the gold standard for diagnosis of gestational diabetes?
2hr 75g oral glucose tolerance test
FPG; 5.6 mmol/l
2hr OGTT; 7.8 mmol/l
At what gestation is the fundal height around the umbilicus?
20 weeks
At what gestation is the fundal height at the xiphisternum?
36 wks
What are major risk factors for SGA foetus?
Maternal age over 40 Smoker > 11 cigs Paternal SGA Cocaine Daily vigorous exercise Previous SGA baby Previous stillbirth Materna SGA Chronic hypertx Diabetes with vascular disease Renal impairment Antiphospholipid syndrome Heavy bleeding similar to menses PAPP-A < 0.4 MoM
What screening is performed for SGA foetus?
Reassess at 20 wks
PAPP-A <0.5 MoM
Foetal echogenic bowel
What should be performed if baby still small at 20 weeks?
Serial assessment of foetal size and umbilical artery doppler from 26-28 weeks
Reassess during 3rd trim
How is foetal growth assessed?
Serial measurement of SFH at each antenatal app from 24wks of pregnancy
Plot SFH on customiased chart
At what cut off should women with a reduced SFH have further assessment?
Below 10th centile or serial measurements which demonstrate slow or static growth by crossing centiles
Refer for USS measurment
In what conditions is SFH inaccurate?
BMI >35
Large fibroids
Hydraminos
What are the major risk factors for pre-eclampsia?
Hypertensive disease in a previous preg CKD Autoimmune disease such as SLE or APS T1DM or T2DM Chronic hypertx
What is the treatment for high risk patient groups for PET?
75 mg of aspirin daily from 12 wks until birth at baby
What are the moderate risk factors for PET?
First preg Age 40 or over Pregnancy interval of >10 years BMI >35 FMHx of PET Multiple pregnancy
What is the recommendation for women with more than 1 moderate risk factor for PET?
75mg of aspirin from 12 weeks until birth of baby
What is urinalysis assessing in antenatal screening?
UTI
Asymptomatic bacteriuria (send MSSU for C+S)
PET; proteinuria
Diabetes
What are the minor RF for SGA foetus?
Maternal age >35 IVF singleton Nulliparity BMI <20 BMI 25-34.9 Smoker 1-10 cigs Low fruit intake pre-preg Previous PET Pregnancy interval <6 months Pregnancy interval >60 monthd
How many minor risk factors are needed to warrant further screening for SGA?
3 or more
How should SGA be assessed if minor risk factors are found?
Reassess at 20 wks PAPP-A <0.4 Foetal echogenic bowel Uterine artery doppler at 20-24 weeks Assessment of foetal size and umbilical artery doppler in 3rd trim
What ia nuchal thickness?
Measure of skin thickness behind foetal neck using USS
Assess fluid levels
What is considered an abnormal nuchal thickness?
<3.5 mm when CRL is between 45-85mm (11-13 +6)
