## First Trimester Antenatal Screening Investigations **Key Point:** Oral glucose tolerance test (OGTT) is **not** part of the first trimester routine investigations. Gestational diabetes screening is typically performed in the **second trimester (24–28 weeks)**, not the first trimester. ### First Trimester Investigations (Routine ANC Package) | Investigation | Purpose | Timing | | --- | --- | --- | | Blood group & Rh typing | Transfusion compatibility, Rh sensitization risk | 1st visit (1st trimester) | | Complete blood count (CBC) | Screen for anemia, infections | 1st trimester | | Blood pressure recording | Baseline BP, hypertension screening | 1st visit | | Urine routine & microscopy | Screen for UTI, proteinuria, glycosuria | 1st trimester | | VDRL/RPR test | Screen for syphilis | 1st trimester | | HIV testing | Screen for HIV | 1st trimester | | Hepatitis B & C serology | Screen for viral hepatitis | 1st trimester | | Abdominal ultrasound | Confirm pregnancy, dating, anomalies | 1st trimester | ### When OGTT is Performed **High-Yield:** Gestational diabetes screening via OGTT is performed in the **second trimester at 24–28 weeks** of pregnancy, not in the first trimester. Early screening (before 24 weeks) is only indicated in high-risk women (obesity, family history of diabetes, previous GDM). **Mnemonic:** **FIRST TRIM** — Blood group, CBC, VDRL, HIV, HBsAg, HCV, Urine, Ultrasound (NOT glucose tolerance test) **Clinical Pearl:** Routine OGTT in the first trimester is not recommended because gestational diabetes typically manifests in the second and third trimesters due to increasing insulin resistance with advancing pregnancy.
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