Fetal Blood Sampling

Question 1

ph ≥ 7.25

Answer 1

Normal pH. No further action required.

Question 2

pH 7.2-7.25

Answer 2

Borderline.

Repeat in 30 minutes or delivery if its a rapid fall since the last sample

Question 3

pH ≤ 7.20

Answer 3

Abnormal
Deliver
MOD depends on cervical dilatation

Question 4

When is FBS contraindicated?

Answer 4

FBS is contraindicated in women who are HIV/Hep B/Hep C positive.

Or if there is a possibility that the baby may have a bleeding disorder.

Question 5

When is a fetal blood sample indicated?

Answer 5

Following a non-reassuring CTG and obstetrician reviews and decides to either deliver or take a fetal blood sample

Question 6

What does a fetal blood sample do?

Answer 6

Enables evaluation of the fetal acid-base status

During each contraction the maternal blood flow through the placenta is impeded, this obstructs the venous flow and then the arterial flow

The fetus is usually unaffected by this
but if the uterine contractions are prolonged or
there is previous impairment of placental function
then fetal hypoxia, hypercapnia and respiratory acidosis occur with a fall in pH
In severe hypoxia the fetal tissues undergo anaerobic glycolysis, which produces lactic acid and reduces the pH further

Question 7

How do you take a fetal blood sample?

Answer 7

1. patient in left lateral position
2. insert amnioscope through the vagina and visualise scalp
3. clean and dry the area and spray on ethyl chloride which induces capillary action and numbs the area
4. then insert your scope with tiny blade make incision to vein and collect small sample of blood in capillary tube
5. analyse pH