Antenatal Screening Flashcards
What is difference between diagnostic and screening test?
Screening - no symptoms, evaluate individual’s risk of developing a disease whereas diagnostic - symptoms often, identifies presence of specific disease
How do we assess the robustness of a screening test?
Sensitivity and specificity
What blood tests are carried out at booking visit? (6)
Hb, ABO; Rhesus status and antibodies, syphillis; HIV; Hep B + C, urinalysis
What is the purpose of the ultrasound performed at booking scan? (5)
Confirm viability, singleton/multiple pregnancy chorionicity, estimate gestational age & EDD, detect major structural abnormalities, offer trisomy screening
What is Naegele’s Rule?
Predicts an estimated due date based on the onset of woman’s last menstrual period. Add on nine months and seven days (280 days)
What are 3 possible reasons for an empty gestational sac in uterus in ultrasound?
anembyronic thus non-viable,
OR very early so no foetal pole visible yet,
OR pseudosac which is caused by hormone reaction in ectopic pregnancy
What history (3) and examinations (6) are done at antenatal midwife appointment?
History: Physical & mental health, fetal movements. Examinations: BP, urinalysis, symphsis-fundal hieght, lie and presentation, engagement of presenting part, fetal heart auscultation
List 11 conditions screened for in the 20 week scan.
Edward's syndrome, Patau's syndrome, anencephaly, spina bifida, cleft lip, congenital diaphragmatic hernia, gastroschisis, exomphalos, congenital heart disease, bilateral renal agenesis, lethal skeletal dysplasia
The combined test screens for what conditions and between what weeks is it carried out?
Screens for Down’s, Edward’s and Patau’s syndrome and is carried out between 10-14 weeks
What is the combined test?
Combined blood test (HCG and PAPP-A),
USS to check nuchal translucency/nuchal thickness
The quadruple test screens for what condition and what weeks of pregnancy is it carried out?
Screens for just Down’s syndrome and is carried out between 14-20+6 weeks
What is the quadruple test?
Maternal age, gestation and levels of bHCG, unconjugated estriol (UE3), alpha-fetoprotein, inhibin A
Which is more accurate - combined or quadruple test?
Combined more accurate for screening for Down’s syndrome
Major structural abnormalities occur in what percentage of pregnancies?
2-3%
What is placenta praevia and at what scan is it identified?
Low-lying placenta that covers all or part of the cervix, identified at the anomaly scan (AKA 20 week scan)
When are normal pregnancy USS scans?
10-14 weeks (12 week) and 18-21 weeks (20 week)
What is the management plan if the placenta is seen to be lying low on anomaly scan?
Placental site is rechecked at 32 weeks by USS, sometimes transvaginal
What are 2 conditions that can cause increased nuchal thickness?
Chromosomal abnormalities and fetal heart abnormalities
What are the approximate sensitivity and false positive rates for combined test?
95% sensitivity and 5% false positive
A value of < what is considered normal NT?
<3.5mm
What is CRL and what is it used to measure?
Crown Rump length - the length of the foetus from top of the head to bottom of torso. It’s used in early pregnancy to measure gestation
The CRL must be between what mm for first trimester trisomy risk assessment NT test to be carried out?
Between 45 and 84mm
What is offered as a secondary screening test if high chance result for any trisomy test?
Non-invasive prenatal testing: analysis of circulating fetal DNA fragments in maternal blood
Trisomy assessment >1:150 is high risk. What should be carried out next?
NIPT or CVS/amniocentesis
NIPT (AKA cell free fetal DNA (cffDNA)) is accurate from around how many weeks pregnancy?
around 10 weeks
cffDNA is less accurate than the combined test for identifying risk of Down’s syndrome. True/false?
False - more accurate
What is the approximate sensitivity and false positive rate of NIPT?
What can cause the false positive rate?
Sensitivity rate: >99% and false positive rate: <0.1%. False positive rate could be caused by placenta having trisomy but not foetus
Chorionic villus sampling carries a miscarriage rate of 2%. After how many weeks is it usually performed?
after 12 weeks
Aminocentesis carries a miscarriage rate of 1%. After how many weeks is it usually performed?
after 15 weeks
What is the difference between sickle cell disease and thalassemias genetically and clinically?
Genetically: sickle cell affected have two abnormal haemoglobin genes whereas thalassemia affected has missing genes
Thalassaemia can cause symptoms when there are >2 genes. The severity of anaemia in thalassemias depends on the number of genes missing. True/false?
True
What is the worldwide leading cause of maternal death?
Postpartum haemorrhage
Maternal aneamia is common and can be caused by what 3 deficiencies? Which is most common?
Iron (most common), folate and B12 deficiency
When are mothers screened for anaemia?
Screened at booking and at 28 weeks
When are mothers blood group and red cell antibodies status checked?
At booking scan and at 28 weeks
When should non-invasive fetal genotyping (of D, C, c, E, e and K antigens) using maternal blood be carried out?
Should be done for relevant antigen when maternal red cell antibodies are present
How does Rhesus haemolytic disease develop?
Rhesus -ve mother has rhesus +ve baby, rhesus +ve blood cells can enter mother at delivery or sensitising event, rhesus antibodies produced by mother, rhesus antibodies then attack next pregnancy’s red blood cells
What can cause fetal hydrops?
Haemolytic disease of the newborn
When is Anti-D given to pregnant women?
Given routinely at 28weeks to Rh-ve mothers and after any sensitising event, also given again afer birth if baby Rh+ve
List 5 risk factors for gestational diabetes that should be identified at the booking appointment.
- BMI >30kg.m2
- previous macrosomic baby weighing >4.5kg
- previous gestational diabetes
- FH diabetes (first-degree relative)
- minor ethnic family origin with high prevalence of diabetes
Who should be offered testing for gestational diabetes? What is the diagnostic test?
Women with any one of the 5 risk factors. Test is the 2-hr 75g oral glucose tolerance test. +ve gestational diabetes if woman has either a fasting plasma glucose level of 5.6mmol/l or above OR a 2-hour plasma glucose level of 7.8mmol/L or above
What is recommended at each antenatal appointment from 24 weeks pregnancy?
Symphysis fundal height measuring to improve prediction of SGA neonate
Who should be referred for USS measurement of fetal size? (2) Which needs serial SFH measurements?
Women with a single SFH which plots below 10th centile or serial measurements which show slow growth AND
women who won’t be able to accurately measure SFH e.g. BMI>35, fibroids, hydramnios - these need serial SFH measurements
List 5 examples of women at high risk of pre-eclampsia.
Women with hypertensive disease in previous pregnancy, CKD, autoimmune disease (e.g. lupus or antiphospholipid), T1/T2 DM, chronic hypertension
Women at high risk of pre-eclampsia should be managed how?
Should take 150mg aspirin daily from 12wks to 36 wks
List 6 examples of women with moderate risk of pre-eclampsia.
First pregnancy, age 40 or above, pregnancy interval >10yrs, BMI of 35kg/m or more, FH pre-eclampsia, multiple pregnancy
Women with more than one moderate risk of pre-eclampsia are managed how?
Should take 150mg daily from 12 weeks until birth
What 4 problems does urinalysis screen for?
UTI, asymptomatic bacteriuria (associated with risk of miscarriage, sepsis), proteinuria (pre-eclampsia) and diabetes
In which scan are the following tests carried out?
Haemogloinopathies, Hep B & C, HIV, Syphillis, red cell antibodies, anaemia, no. foetuses, viability, PMH, PSH, obstetric Hx, DH, allergies, SH, FH, past mental health history, FGM, BMI. Trisomy screening offered
Booking
In which scan are the following tests carried out?
Cleft, heart, limb, neural tube & abdo wall defects, lung, brain and urinary tract abnormalities, placental site and diaphragmatic hernia
20wk anomaly scan
In which scans are the following tests carried out?
red cell antibodies and anaemia
Booking & 28wk
In which scan are the following tests carried out?
BP, urine, macrosomia/IUGR, mental health, abuse and support
All ANC
CRL is useful as a measurement of gestational age from 6-13weeks. What is used afterwards?
Head circumference, biparietal diameter and femur length
After what maternal age does risk of Down’s Syndrome steeply increase?
from age 40
