# Thrombotic Microangiopathy TTP and HUS in Pregnancy

> NEET-PG Obstetrics and Gynaecology notes on thrombotic microangiopathy in pregnancy, separating TTP and HUS from HELLP using ADAMTS13 and plasma exchange.

- Canonical URL: https://prepelephant.com/topics/neet-pg/obstetrics-and-gynaecology/thrombotic-microangiopathy-ttp-hus-in-pregnancy
- Exam / course: NEET-PG · Subject: Obstetrics and Gynaecology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-14
- Last updated: 2026-10-14
- Reference basis: Williams Obstetrics; Dutta's Textbook of Obstetrics; Harrison's Principles of Internal Medicine
- How to cite: "Thrombotic Microangiopathy TTP and HUS in Pregnancy", PrepElephant, https://prepelephant.com/topics/neet-pg/obstetrics-and-gynaecology/thrombotic-microangiopathy-ttp-hus-in-pregnancy

## Direct answer

Thrombotic microangiopathy in pregnancy is a group of disorders in which microangiopathic haemolytic anaemia and thrombocytopenia follow widespread microvascular clotting. Thrombotic thrombocytopenic purpura results from severe deficiency of the ADAMTS13 enzyme, whereas haemolytic uraemic syndrome is driven mainly by complement dysregulation or Shiga toxin and mostly injures the kidney. Plasma exchange is the mainstay of treatment for TTP, and the key decision is separating it from HELLP.

## What you must remember

- **Core features:** microangiopathic haemolytic anaemia with schistocytes, thrombocytopenia and end-organ injury; a raised LDH with low haptoglobin supports ongoing haemolysis.
- **TTP pentad:** fever, thrombocytopenia, haemolytic anaemia, renal dysfunction and neurological symptoms, although all five are not always present at once.
- **ADAMTS13 deficiency:** activity below about 10 per cent is the basis for diagnosing TTP, and this assay is the test that separates TTP from HELLP.
- **HELLP:** haemolysis, elevated liver enzymes and low platelets, a complication of pre-eclampsia that usually improves after delivery, with ADAMTS13 activity usually above 10 per cent.
- **HUS:** renal failure predominates; typical HUS follows Shiga toxin-producing Escherichia coli diarrhoea, while atypical HUS reflects defects in complement regulation.
- **Treatment:** plasma exchange with fresh frozen plasma and corticosteroids, with caplacizumab or rituximab reserved for selected or refractory cases.
- **Platelet transfusion:** generally avoided in TTP because platelets can feed microvascular thrombosis, unless bleeding is life-threatening.

## A stepwise approach from smear to plasma exchange

A third-trimester woman with a falling platelet count and a rising creatinine needs a quick decision between HELLP and TTP. The sequence below places the test that separates the two early, because the treatment that follows is very different.

1. **Confirm microangiopathy:** a peripheral smear showing schistocytes, with raised LDH and low haptoglobin, establishes the haemolysis.
2. **Check the coagulation screen:** the profile is usually normal in TTP and HELLP, whereas disseminated intravascular coagulation shows a prolonged clotting time, low fibrinogen and raised D-dimer.
3. **Send ADAMTS13 activity:** activity below about 10 per cent points strongly to TTP, but the result can take days, so treatment starts without waiting when suspicion is high.
4. **Start plasma exchange urgently:** daily exchange with fresh frozen plasma continues until platelets recover and haemolysis settles, and corticosteroids are commonly added.
5. **Consider adjuncts:** caplacizumab shortens time to platelet recovery when given alongside exchange, and rituximab is reserved for relapse or refractory disease.
6. **Time delivery on obstetric grounds:** delivery does not cure TTP, and the disease can persist or relapse after birth, so exchange continues through the puerperium.

## Where the exam tries to catch you

Vignettes lean on a hypertensive woman with thrombocytopenia and expect a reflex answer, so the two conditions must be separated by the test rather than by the pattern alone.

- **Trap:** Calling every postpartum thrombocytopenia with haemolysis HELLP. — **Correct:** Fever, neurological signs and very low ADAMTS13 activity indicate TTP, which needs plasma exchange rather than delivery alone.
- **Trap:** Transfusing platelets to correct a low count in TTP. — **Correct:** Platelets are generally avoided because they can add to microvascular thrombi unless bleeding is life-threatening.
- **Trap:** Treating HUS with plasma exchange by default. — **Correct:** Typical HUS is managed with supportive care and dialysis when needed, whereas atypical HUS may need complement inhibition.

## Frequently asked questions

### Which test distinguishes TTP from HELLP in pregnancy?
ADAMTS13 activity distinguishes the two conditions. Activity below about 10 per cent favours thrombotic thrombocytopenic purpura, whereas HELLP syndrome usually keeps activity above that level. Because results take time, treatment decisions rely on the clinical picture while the assay is awaited.

### Why is plasma exchange used in thrombotic thrombocytopenic purpura?
Plasma exchange replaces the missing ADAMTS13 enzyme and removes the inhibitory antibodies and ultra-large von Willebrand multimers. It is started urgently and continued until platelets recover and haemolysis stops. Stopping early risks relapse.

### Does delivery cure thrombotic thrombocytopenic purpura in pregnancy?
Delivery does not cure TTP, and the disease can persist or relapse after birth. Plasma exchange must continue after delivery until the platelet count and haemolysis resolve. Obstetric timing is decided on fetal and maternal grounds.

### What is the typical cause of haemolytic uraemic syndrome?
Typical haemolytic uraemic syndrome usually follows infection with Shiga toxin-producing Escherichia coli, classically O157:H7, which causes bloody diarrhoea before renal injury. Atypical haemolytic uraemic syndrome is linked to defects in complement regulation and can recur.

### Why should platelets generally not be transfused in thrombotic thrombocytopenic purpura?
Platelets can aggregate into existing microvascular thrombi and may worsen the thrombosis. In TTP, transfusion is generally reserved for life-threatening bleeding. Clinicians weigh the bleeding risk against this concern before any transfusion.