A single site observational study aiming to:

(i) Identify cases of previously undiagnosed thrombotic thrombocytopenic purpura (TTP) and atypical haemolytic syndrome (aHUS) in a cohort of women with complicated pregnancies (ii) Characterise the clinical features of these cases and (ii) Identify clinical features or biomarkers which may help distinguish TTP/aHUS from other complications of pregnancy such as preeclampsia

Inclusion Criteria:

- Women, either currently pregnant or recently postpartum, and affected by one or more of the following complications in the index pregnancy: (i) Preeclampsia with evidence of end organ damage (renal/ liver/ haematological/ neurological) or uteroplacental dysfunction (FGR/IUFD) (ii) HELLP syndrome (iii) Fetal growth restriction (FGR) (growth <10th centile) that is unexplained (ie not due to infection, fetal structural anomaly, fetal chromosomal or pre-existing maternal medical problem) (iv) Intrauterine fetal demise (IUFD) after 20 weeks' gestation that is unexplained (v) Unexplained new onset renal impairment (defined by serum creatinine >85umol/L 1st trimester, or >80umol/L 2nd trimester, or >90 umol/L 3rd trimester[32]; OR an increase in serum creatinine by (i) at least 1.5 times the baseline or (ii) of equal or greater than 26.5umol/L (as per KDIGO criteria) (vi) Unexplained new onset thrombocytopenia (platelets <75x10^9/L)

Exclusion Criteria:

• Previous diagnosis of TTP or aHUS
• Known disorder of complement dysregulation
• Patients not wishing to participate
• Patients aged less than 16
• Patients lacking capacity to provide informed consent

All women receiving obstetric care at University College Hospitals London NHS Trust over the study period