Reference intervals for clinical biochemistry and haematology tests during normal pregnancy.

Background: Pregnancy induces physiological changes which affect biochemical and haematological parameters. As the significance of laboratory test results change throughout pregnancy, the reference interval (RI) or key result interpretive guide should be specific to pregnancy. This study sought to establish trimester-specific-RIs for routine biochemical and haematological tests in healthy white European women with singleton pregnancies with comparison to RIs for non-pregnant European adults.

Methods: A retrospective analysis of a prospective longitudinal single-centre study of healthy pregnant women conducted between November 2018 and December 2020 in a tertiary academic hospital with approximately 3000 births annually. Inclusion criteria: signed informed consent, age ≥18 years, white European, body mass index (BMI) <25 kg/m2, blood pressure <140/90mmHg, non-smoker, no previous pathology or gestational diabetes. Trimester defined as T1: up to 13 weeks + 6 days, T2: 14-27 weeks + 6 days and T3: ≥28-41 weeks + 6 days. Baseline demographics, anthropometric and laboratory measurements were recorded. In total, 31 biochemical and 10 haematological ISO15189:2012 accredited tests were measured using Roche Cobas® and Sysmex XN-9100™ analysers, respectively. RIs were established according to the International Federation of Clinical Chemistry (IFCC) recommended method.

Results: Apparently healthy pregnant women ( = 124) with bio-banked serum samples in each trimester were recruited. At the booking visit, 49.2% ( = 61) of participants were nulliparous, with median age of 34.4 (IQR: 31.3-37.3) years, gestational age of 89 (IQR: 84-93) days, BMI of 22.5 (IQR: 21.0-23.7) kg/m and systolic and diastolic blood pressure of 116 (110-125) mmHg and 67 (61-75) mmHg, respectively.

Conclusions: Normative trimester-specific biological intervals for routinely requested biochemical and haematological medical laboratory tests were established. These RIs will be invaluable to result interpretation and the management of pregnant women.