Pregnancy tutorial

Question 1

What is the aim for carrying out an early pregnancy scan?

Answer 1

Hope to find info such as:

confirm viability

Singleton/multiple pregnancy and chorionicity

Estimate gestational age – explain most accurate time /method to establish EDD/estimated due date (+/3 days)

Detect major structural anomalies that may be identified in early pregnancy- for example anencephaly (congenital defect where large part of skull is absent along with cerebral hemisphere of brain).

Question 2

Difference between screening test and diagnostic test?

Answer 2

Screening tests do not tell us for sure whether a baby is affected by a condition. They only show there is a higher risk.

Diagnostic tests tell us for sure. Low risk screening doesn’t mean no risk. High risk screening doesn’t mean baby is affected.

Question 3

How to assess robustness of a screening test?

Answer 3

Sensitivity and specificity

Sensitivity = True positive /(positive + false negative)
Specificity = True negative/(negative + false positive)

Question 4

What is nuchal translucency (NT)?

Answer 4

The nuchal translucency test measures the nuchal fold thickness.

This is an area of tissue at the back of an unborn baby’s neck. Measuring this thickness helps assess the risk for Down syndrome and other genetic problems in the baby.

Question 5

When is NT test valid?

Answer 5

From 11 – 14 weeks of gestation or from CRL 45 – 84mm

Question 6

Normal NT test value?

Answer 6

Less than or equal to 3.5mm

Question 7

What may prevent NT test from being done?

Answer 7

BMI, fetal position, late booker

Question 8

What can cause an increased nuchal translucency?

Answer 8

Chromosomal abnormality e.g. T12, T18, T21, Turners Syndrome (46 XO), triploidy

Underlying fetal abnormality (cardiac common). Sometimes idiopathic.

Bigger it is more likely a pathological cause.

Question 9

For genetic abnormalities, what additional tests would be done?

At what period of gestation and what are the pros and cons?

Answer 9

Chorionic villus sampling (CVS): 11-14 weeks, diagnostic test.
pro:definitive answer
con: 2% risk of miscarriage, occasionally insufficient sample or cells do not culture

Amniocentesis:15 weeks onwards, diagnostic test
pro:definitive answer
con: 1% risk of miscarriage

Question 10

Is NIPT a screening test or diagnostic test?

Answer 10

Screening test

Question 11

When is NIPT (non-invasive prenatal testing) used?

Answer 11

first line choice after high risk first trimester screening. When screening for trisomies 21, 18 and 13

Question 12

What is MSAFP?

Answer 12

Maternal Serum alpha feto protein

Question 13

Elevated MSAFP seen in multiple pregnancies is physiological but what is the common feature of gastroschisis and spina bifida that results in elevated MSAFP?

Answer 13

Exposure of internal organs to surface- foetal circulation in closer contact with amniotic fluid

In spina bifida, neural tube is not fully formed and is exposed to amniotic fluid.

Similar concept with gastroschisis but areas of abdomen such as intestines are exposed.

Question 14

Which components of antenatal care are routine (common for all pregnant women)?

Answer 14

Initial appointment at 12 weeks: routine assessments/investigations: BP, weight, urinalysis, haemoglobin, ultrasound scan to date.

Further appointments: 20, 24, 28, 32 week. At each appointment BP urinalysis, abdominal palpation, fetal heart heard.

From 36 weeks onward: presentation +/- relation to brim assessed.

Routine screening offered, recommended and delivered.