Enhanced urinary albumin excretion after 35 weeks of gestation and during labour in normal pregnancy

This study reports on the urinary albumin to creatinine ratio during normal pregnancy, with special emphasis on the pre-delivery and labour periods. Albumin was determined in single voided urine specimens obtained from healthy non-pregnant women (n = 16) and healthy pregnant women (n = 203; Groups A and B, 133 females examined during clinic visits and presentation at obstetric department; Group C, 70 females examined during labour) by radio-immunoassay (RIA). The mean ratio (±SD) for albumin/creatinine (A/Cr) in non-pregnant women was 1.46 ± 0.32 mg mmol^-1 Cr. Thus, 2.10 mg mmol^-1 Cr (mean + 2 SD) was considered to be the upper limit of normo-albuminuria. During pregnancy, 73% of the women (97 out of 133, Groups A and B) excreted ±2.10 mg mmol^-1 Cr. During the first 35 weeks of gestation, 30 of 34 pregnant women (88%) excreted ≤2.10 mg mmol^-1 Cr, the mean being 0.93 ± 0.64 mg mmol^-1 Cr (median 1.0 mg mmol^-1). During 36-42 weeks of gestation, the median A/Cr was 1.93 mg mmol^-1 Cr (range 0.43-12.16) and 32 of 99 (32%) had values >2.10 mg mmol^-1 Cr, an increase of more than two-fold (p < 0.031) compared with the first 35 weeks. During labour, 61% of non-haematuric urines (33 of 54, Group C) were >2.10 mg mmol^-1 Cr, being 125% greater (p < 0.006) than that observed during pregnancy. Thus in normal pregnancy, A/Cr is increased during the late period of pregnancy and during labour.