Trimester-Specific Reference Intervals and Comparative Analysis of Glycated Haemoglobin, Fasting Plasma Glucose and Full Blood Count Parameters among Non-Diabetic Pregnant Women Attending a Nigerian Maternity Hospital: A Cross-Sectional Study

Aims

To determine trimester-specific reference intervals and compare glycated haemoglobin (HbA1c), fasting plasma glucose (FPG) and full blood count (FBC) parameters between second- and third-trimester non-diabetic pregnant women. Study Design: Cross-sectional comparative study. Place and Duration of Study: Antenatal clinic of Adeoyo Maternity Teaching Hospital, Yemetu, Ibadan, Oyo State, Nigeria, between August and September 2025. Methodology: Two hundred and fifty (250) consenting pregnant women aged 18–45 years (138 in the second trimester, 112 in the third trimester) were consecutively recruited. Women with a pre-existing diagnosis of type 1 or type 2 diabetes were excluded, and non-diabetic pregnancy status was further operationally defined using each participant’s routine antenatal gestational diabetes mellitus (GDM) screening record: only women who had undergone the standard 75-g oral glucose tolerance test (OGTT) at 24–28 weeks (or, for third-trimester enrolees screened earlier, at booking) and screened negative by International Association of Diabetes and Pregnancy Study Groups (IADPSG)/WHO 2013 criteria (fasting plasma glucose <5.1 mmol/L, 1-hour <10.0 mmol/L, 2-hour <8.5 mmol/L) were retained. Socio-demographic, obstetric and lifestyle data were obtained with a structured questionnaire. Fasting plasma glucose was determined by the glucose oxidase method, HbA1c by turbidimetric inhibition immunoassay, and FBC parameters by an automated haematology analyser; daily internal quality control was run on all three platforms, with assay coefficients of variation of <5% for FPG, <3% for HbA1c and <5% for FBC parameters, within manufacturer-stated limits. Data were analysed in SPSS version 25 using an independent-samples t-test, Pearson correlation, and percentile estimation (2.5th–97.5th) for trimester-specific reference intervals; mean differences are reported with 95% confidence intervals (CI) and Cohen’s d as a measure of effect size; P < 0.05 was considered significant.