ITP and VWD in Obstetrics

This came up in the CRQs in September 2024.

It also comes up on labour ward.

Take home messages

• Low platelets (but >100) in the third trimester is usually gestational thrombocytopenia
• Risks of neuraxial blockade need to be assessed on an individual basis
• The platelet count may be acceptable, but the platelet function may still be deranged

What normally happens

We like platelets, generally speaking, when managing a situation where one human needs to exit another and their blood supplies are required to separate.

Platelets, clotting factors and blood vessels all work together to establish a fine balance of continuous clotting, anticoagulation and fibrinolysis.

This means that when something bad happens - like blood vessel trauma - the see-saw can easily and rapidly be tipped in the 'make a clot' direction, and an appropriately substantial and potentially life-saving haemostatic response can be produced.

If this doesn't happen properly, for whatever reason, then... well...

So what about the platelets?

Blood volume expands significantly in pregnancy, to prepare the mother's body for the blood loss that comes with birthing a baby.

As part of this dilution, many blood components see a drop in concentration (e.g. physiological anaemia of pregnancy).

The commonest cause of a third trimester dip in platelet number is gestational thrombocytopenia and pre-eclampsia is another cause not to forget.

What is ITP?

Immune thrombocytopenia is an autoimmune condition that affects up to 1 in 1000 pregnancies, resulting in sequestration of platelets that can see the number drop well below 100.

The low platelet count is rather suboptimal in patients needing major abdominal surgery, preferably under neuraxial anaesthesia.

In around 65% of cases the condition was already there, but might not have reared its head until pregnancy.

What actually happens

• IgG against platelet membrane glycoproteins
• Sticks to platelets and is sequestered by the spleen

Treatment for ITP

Surprise surprise it's the same as pretty much every other autoimmune condition we see:

• Steroids (pred 10-20mg OD) - 66% will see a rise in platelets within a week
• IVIG 0.5 g/kg - if no response to steroids or more unwell

Can I do a spinal?

The study referenced below found not one complication from neuraxial anaesthesia in around 130 pregnancies complicated by ITP (and not complicated by pre-eclampsia etc).

Some of these had platelets as low as 45.

Weirdly enough, in ITP, platelet function is thought to be even better than usual, meaning that as long as their platelet count is stable above 75, there isn't any increased bleeding risk from central neuraxial procedures.

• Remember a spinal needle carries much lower risk than a Tuohy

The decision needs to be made on an individual basis each time, the question being 'is neuraxial higher risk than GA?'

• An early, calm epidural may allow a woman to deliver naturally, who may otherwise had required a C section
• A spinal might be far lower risk than a GA for an emergency section for a woman with airway concerns, obesity or other medical issues
• A slim patient with platelets below 50 and previous neurological issues in the lower limbs might be better off with a general anaesthetic, but this will need proper counselling beforehand

What to do about it

The standard answer is 'early haematology input and MDT management'.

Good communication with the patient to explain the relevant risks both to mother and baby.

As a trainee or non-consultant, you need to be escalating early and discussing with senior colleagues.

• A generalist DGH anaesthetist might give you a different answer to a tertiary centre obstetric anaesthetist

Tell me about Von Willebrand

In 1924, Finnish doctor Erik Adolf von Willebrand noticed that a 5 year old girl, and many members of her family, had a strange bleeding condition that wasn't haemophilia.

It is now the most common congenital bleeding disorder, but only appears to be clinically significant in around 1 in 10 000 people.

VWF is a glycoprotein that glues together platelets and factor 8 during clot formation.

• VWF concentrationsnormally increase up to threefold during pregnancy
• If they don't, or their activity is less than perfect, then the risk of bleeding increases dramatically
• 15 - 30% will have primary PPH
• 25% will have secondary PPH

Any parturient with known severe VWD of any type should be managed on a specialist obstetric unit with haemophilia experts nearby.

Can we treat VWD?

Much of the time it's just supportive care and lots of close monitoring, but you can actively increase VWF levels with desmopressin or VWF concentrates.

• Desmopressin 0.3mg/kg IV or SC- triggers release of stored VWF from endothelial cells

Will usually bump VWF levels up by 2-3x, just note that it can also cause water retention and hyponatraemia.

• VWF concentrates are generally used in Type 2 and Type 3 VWD as desmopressin doesn't do much for these people
• You can also give platelets as these contain some VWF too

Can I do a spinal?

If they have Type 1 VWD, with adequate VWF activity and Factor 8 activity (above 0.5), with normal platelets and normal clotting function then yes.

Magic platelet numbers

We don't technically know the true minimum safe threshold for performing a spinal or epidural, and remember it's not just the number of platelets, but their function that matters.

Your platelet count could be over 250 but if you took clopidogrel this morning, they ain't doing squat.

The estimated risk of an epidural haematoma

• 0.2% for platelets of 70 - 100
• 3% for 50 - 69
• 11% for 0 - 49

The key is to decide whether this risk outweighs the risk of the alternative - general anaesthesia - and all the possible harms that it brings, such as:

• worse pain relief
• slower recovery
• airway risk
• PONV
• Psychological distress of not being present for birth of baby

If you're giving platelets then you probably want to be giving IVIG as well, because otherwise your precious gifted platelets are rapidly going to be consumed as well, leaving you back precisely where you started.

Useful Tweets and Resources

References and Further Reading

Primary FRCA Toolkit

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