Objectives  Circulating concentrations of the peptide kisspeptin have been proposed as a novel biomarker for early detection of pre‐eclampsia. Our aims were to assess analytical and clinical performance characteristics of a commercial kisspeptin assay and to determine sensitivity and specificity of the test for pre‐eclampsia.

Design  Prospective, longitudinal study in a United Kingdom tertiary referral Antenatal Metabolic Clinic.

Patients  Severely obese (body mass index, BMI > 40kg/m², n = 194) and lean (BMI < 25kg/m², n = 78) pregnant women.

Measurements  A commercial kisspeptin ELISA (Phoenix Pharmaceuticals) was assessed for analytical sensitivity, specificity, precision, linearity, recovery and stability in maternal plasma samples at 16, 28 and 36 weeks gestation. Pre‐eclampsia, defined using International Society for the Study of Hypertension in Pregnancy guidelines; blood pressure; delivery gestation; birthweight.

Results  Kisspeptin concentrations were lower in early pregnancy in obese women (P < 0·001), and in women who later developed pre‐eclampsia (P < 0·05), compared with women with uncomplicated pregnancies. For 16‐week plasma kisspeptin in prediction of pre‐eclampsia, area under the receiver‐operator characteristic curve was 0·80 (P < 0·01), positive and negative likelihood ratios were 3·0 and 0·2, and test sensitivity and specificity were 85·7 and 71·4%, respectively. In regression analyses, kisspeptin (16 weeks) associated positively with delivery gestation (P < 0·05) and birthweight (P < 0·0001), and negatively with 28‐ and 36‐week blood pressure (P < 0·0001).

Conclusions  Kisspeptin concentration in early pregnancy is a promising biomarker for pre‐eclampsia and low birthweight but cannot be recommended, in isolation, for universal screening because of inadequate test sensitivity and specificity. Large‐scale studies are required to assess its potential in a panel of biomarkers.