Antenatal screening and early-pregnancy comparisons

Routine Australian Antenatal Screening Protocols

High-quality antenatal care follows Australian pregnancy care guidelines, designed to screen for maternal infections, genetic conditions, structural fetal anomalies, and metabolic disorders.

First Antenatal Booking Visit Investigations (8 to 10 Weeks)

• Full Blood Count (FBC): Screens for maternal anaemia (haemoglobin $< 110\text{ g/L}$ in first trimester) and baseline thrombocytopenia.
• Infectious Serology Screen:
  • Rubella Immunity: Maternal IgG; non-immune women are vaccinated postpartum with MMR (live attenuated vaccine is strictly contraindicated during pregnancy).
  • Hepatitis B Surface Antigen (HBsAg): If positive, prompts maternal viral load assessment, third-trimester tenofovir therapy if high load, and newborn hepatitis B immunoglobulin (HBIG) + hepatitis B vaccine within 12 hours of birth.
  • HIV Serology: HIV 1/2 antibody and p24 antigen testing; allows immediate antiretroviral therapy (ART) to prevent vertical transmission.
  • Syphilis Serology: Treponemal EIA screening; positive cases require rapid treatment with intramuscular benzathine penicillin to prevent congenital syphilis.
• Midstream Urine (MSU) Culture: Universal screening for asymptomatic bacteriuria (defined as $\ge 100,000\text{ CFU/mL}$ of a single pathogen). Untreated asymptomatic bacteriuria carries a 30% risk of progressing to acute maternal pyelonephritis, triggering preterm labour and low birth weight. Treatment with an appropriate oral antibiotic (e.g., cephalexin or amoxicillin-clavulanate) for 5 to 7 days is mandatory, followed by a test-of-cure culture.
• Serum Ferritin: Evaluates maternal iron stores and guides oral iron supplementation.

First-Trimester Aneuploidy Screening

1. Combined First-Trimester Screening (cFTS) (performed between $11^{+0}$ and $13^{+6}$ weeks):
   • Combines maternal age, ultrasound measurement of fetal nuchal translucency (NT), and maternal serum biochemistry:
     • Pregnancy-Associated Plasma Protein-A (PAPP-A)
     • Free $\beta$-human chorionic gonadotropin (free $\beta$-hCG)
   • Trisomy 21 (Down syndrome) profile: Increased nuchal translucency, decreased PAPP-A, and elevated free $\beta$-hCG.
   • Trisomy 18 (Edwards) and Trisomy 13 (Patau) profile: Increased nuchal translucency, decreased PAPP-A, and decreased free $\beta$-hCG.
2. Non-Invasive Prenatal Testing (NIPT):
   • Analyzes circulating cell-free fetal DNA (cfDNA) derived from the placenta in maternal plasma, available from $10^{+0}$ weeks gestation onward.
   • Achieves $> 99\%$ sensitivity and specificity for Trisomy 21, and high detection rates for Trisomies 18 and 13 and sex chromosome aneuploidies.
   • Critical Rule: NIPT is an advanced screening tool, not a diagnostic test. An abnormal or "high-risk" NIPT result mandates definitive diagnostic confirmation via invasive testing (chorionic villus sampling [CVS] at 11 to 14 weeks, or amniocentesis from 15 weeks onward) prior to irreversible clinical decision-making.

Mid-Trimester Routine Morphology Scan (18 to 20+6 Weeks)

• Detailed structural assessment of fetal anatomy: central nervous system (ventricles, cerebellum), face/palate, cardiac four-chamber view and outflow tracts, spine, diaphragm, anterior abdominal wall, kidneys/bladder, and long bones.
• Placental localisation: Identifies low-lying placenta or placenta praevia relative to the internal cervical os. If the placental edge lies within $20\text{ mm}$ of the internal os, a repeat transvaginal scan is scheduled at 32 to 34 weeks.

Universal Gestational Diabetes Mellitus (GDM) Screening (24 to 28 Weeks)

• Under ADIPS (Australasian Diabetes in Pregnancy Society) guidelines, all pregnant women undergo a universal one-step 75 g oral glucose tolerance test (OGTT) at 24 to 28 weeks gestation.
• High-risk women (prior GDM, maternal $\text{BMI} \ge 30\text{ kg/m}^2$, maternal age $\ge 40$, polycystic ovary syndrome, family history of type 2 diabetes, or high-risk ethnicity) undergo early testing at booking; if normal, the OGTT is repeated at 24 to 28 weeks.
• ADIPS Diagnostic Thresholds (a single abnormal value establishes the diagnosis of GDM):
• GDM diagnosis (ADIPS 2025): On a 75-g OGTT, one qualifying result establishes GDM: fasting 5.3–6.9 mmol/L, one hour at least 10.6, or two hours 9.0–11.0. Fasting at least 7.0 or two hours at least 11.1 suggests overt diabetes in pregnancy. Routine testing is at 24–28 weeks if diabetes has not already been diagnosed; early assessment is selected by risk.

Clinical Differentiation of Miscarriage Subtypes

• Inevitable: Internal Cervical Os: Open / Dilated; Transvaginal Ultrasound (TVS): Non-viable pregnancy, detached sac, or ruptured membranes; Clinical Symptoms: Heavy vaginal bleeding, progressive abdominal cramping; Primary Management Plan: Expectant, medical (misoprostol), or surgical suction curettage
• Complete: Internal Cervical Os: Bleeding and pain settle after tissue passage; Transvaginal Ultrasound (TVS): Confirm prior IUP or follow PUL until resolved; Clinical Symptoms: Provide return precautions and completion follow-up
• Missed: Internal Cervical Os: Closed; Transvaginal Ultrasound (TVS): Embryo with CRL $\ge 7\text{ mm}$ without cardiac activity, or MSD $\ge 25\text{ mm}$ no embryo; Clinical Symptoms: Asymptomatic or mild spotting; loss of subjective pregnancy symptoms; Primary Management Plan: Expectant observation, medical misoprostol, or elective suction curettage
• Septic: Internal Cervical Os: Usually Open; Transvaginal Ultrasound (TVS): Retained gestational tissue, intracavitary gas, or pelvic fluid; Clinical Symptoms: Maternal fever, foul purulent lochia, exquisite uterine peritonism; Primary Management Plan: Urgent IV ampicillin + gentamicin + metronidazole, fluid loading, surgical curettage

Primary references (checked 7 October 2026): ADIPS 2025 diagnostic recommendations; National Blood Authority anti-D guideline.