Serum PLA2R-negative, biopsy-proven PLA2R-positive primary membranous nephropathy in a dichorionic-diamniotic twin pregnancy.

Primary membranous nephropathy (PMN) in pregnancy is rare and poses significant risks including pre-eclampsia, preterm delivery, low birth weight and fetal death. Anti-phospholipase A2 receptor (PLA2R) antibodies are used to confirm diagnosis.We report a case of biopsy-confirmed PLA2R-positive but seronegative PMN in a woman in her late 20s with a dichorionic-diamniotic twin pregnancy. Initial hypoalbuminaemia was attributed to intercurrent infection but was later recognised as nephrotic syndrome at 20+6 weeks gestation. Renal biopsy at 21 weeks confirmed PMN with positive PLA2R and IgG4 staining, despite negative serum PLA2R antibodies.She was managed with tacrolimus and rituximab, with close monitoring and delivered viable twins via emergency caesarean at 33+3 weeks following premature rupture of membranes. Both maternal disease and neonatal outcomes were favourable. This case highlights the challenges in diagnosing and managing seronegative PMN during pregnancy and supports the role of renal biopsy and rituximab in selected patients.