Dataset used for the paper "Age at Menarche and Blood Pressure in Pregnancy" published in Pregnancy Hypertension and containing data from the Cambridge Baby Growth Study. Uncompressed Microsoft 2013 (.xlsx) file (441 rows including header; 28 columns for standard association analysis; 1753 rows including header; 9 columns for general estimation equation modelling) containing data relevant to the publication collected as part of the Cambridge Baby Growth Study (data collection 2001-2018). All the study participants were recruited from pregnancy clinics at the Rosie Maternity Hospital, Cambridge (2001-2009) around week 15 of pregnancy (when a blood sample for the measurement of serum pregnancy-associated plasma protein A was taken by research nurses). Age at menarche, parity and record of smoking in pregnancy were self-reported and collected as part of pregnancy questionnaires. Blood pressure readings (at four time points in pregnancy), diagnoses of pre-eclampsia and offspring birth weight and gestational age at birth were collected from hospital notes. Fasting blood samples around week 28 of pregnancy were collected by research nurses. Gestational hypertension was defined as either systolic blood pressure >=140 mmHg or diastolic blood pressure >=90 mmHg in any of the blood pressure readings or was recorded from the hospital notes. Gestational hypotension was defined as <=110 mmHg and <=60 mmHg on at least any one occasion, respectively. Pregnancy-associated plasma protein A was measured by fluoroimmunoassay, insulin by enzyme-linked immunosorbent assay and glucose by a standard laboratory technique. HOMA modelling was performed using the online HOMA calculator (https://www.dtu.ox.ac.uk/homacalculator/). The index of multiple deprivation was estimated from residential post codes. Missing data are presented as empty cells. For further information about the study please contact Dr. Clive Petry (address below; email: cjp1002@cam.ac.uk). For further general information about the Cambridge Baby Growth Study please contact Dr. Carlo Acerini (Department of Paediatrics, Box 116, Addenbrooke's Hospital, Cambridge Biomedical Campus, Hills Road, Cambridge CB2 0QQ, U.K.; email: cla22@cam.ac.uk).