Antenatal care, Australian shared care schedule, first and second trimester screening

1. Definition and clinical relevance

Antenatal care is the structured program of clinical assessment, screening, education and risk stratification provided to a pregnant woman from confirmation of pregnancy through to birth.

Purpose:

• Establish accurate gestational age
• Identify and optimise conditions that may affect maternal or fetal wellbeing
• Deliver evidence-based screening
• Provide anticipatory guidance and support

Why early engagement matters:

• Australian guidance recommends attendance by 10 weeks of pregnancy
• Early assessment enables pre-eclampsia risk prediction tools to be useful
• First visit is high-yield: combines dating, comprehensive clinical and psychosocial assessment, screening tests, and initiation of care planning
• Often the point where women needing extra care are first identified

2. Key values, thresholds and decision rules

Standard visit schedule (uncomplicated pregnancy)

Routine screening milestones

Decision rules to remember

• Anaemia: if haemoglobin is low, consider iron supplementation. Investigate a low MCV with haemoglobin electrophoresis or HPLC and exclude iron deficiency (ferritin).
• Aneuploidy pathway: if combined first trimester screening returns high risk, offer NIPT (cell-free DNA); if NIPT is high probability, offer diagnostic testing (chorionic villus sampling or amniocentesis). cfDNA may be an appropriate alternative prior to amniocentesis after a high-risk combined first trimester result.
• GBS: Queensland Health recommends a risk-factor based approach to identify women for intrapartum antibiotic prophylaxis, rather than universal culture screening.
• Previous unexplained stillbirth: consider early GDM screening in addition to routine screening at 26 to 28 weeks.

3. Approach: presentation and differential

History

The first visit is a comprehensive clinical and psychosocial assessment. Establish:

• Last menstrual period and cycle regularity to estimate gestational age and due date.
• Obstetric history: previous pregnancies, mode of birth, complications (previous GDM, pre-eclampsia, preterm birth, unexplained stillbirth).
• Medical and medication history, including anything relevant to the pregnancy that can be optimised.
• Family history and ethnicity (relevant to haemoglobinopathy and carrier screening).
• Psychosocial screen: worries about the pregnancy or social situation, and specifically ask about domestic violence.
• Risk factors for sexually transmitted infections and blood-borne viruses; sensitive risk indicators may not be disclosed, so combine routine testing with risk-based assessment.

Examination

At the first visit and follow-up visits, record:

• Blood pressure and urine for proteinuria (a core pre-eclampsia surveillance combination at every visit).
• BMI at booking.
• From around the second trimester, symphysis-fundal height (SFH) at each visit as a screen for fetal growth.
• Fetal heart auscultation as gestation advances.

Educate about warning symptoms warranting review: ruptured membranes with fluid loss, regular contractions 5 to 10 minutes apart, and (before term) signs of possible premature labour between 22 and 34 weeks.

Differential

Antenatal assessment is largely surveillance rather than diagnosis, but key conditions to actively exclude or detect include: fetal growth restriction (discordant SFH), pre-eclampsia (rising BP, proteinuria), gestational diabetes, anaemia, isoimmunisation (blood group and antibody screen), fetal aneuploidy and structural anomaly, and infection (STI/BBV screen, and considered testing for congenital infection where clinically indicated).

4. Investigations

Bedside

• Blood pressure and urinalysis for proteinuria at first and every subsequent visit.
• Weight and calculated BMI at booking.
• Symphysis-fundal height measurement from the second trimester onward.

Bloods

• Full blood count including MCV; investigate low haemoglobin (consider iron) and low MCV (haemoglobinopathy evaluation and ferritin).
• Blood group and antibody screen.
• Infection screen: HIV, syphilis and hepatitis B should be seen as part of the routine antenatal screen. Chlamydia testing is routinely offered at the first visit to all pregnant people under 30, and regardless of age in high prevalence areas. Self-collected vaginal or urine samples may be used for asymptomatic people.
• Gestational diabetes: fasting glucose or HbA1c at first visit if previous GDM or high risk; routine testing at 26 to 28 weeks per local jurisdiction (in Australia this follows the 2014 ADIPS consensus approach).
• Reproductive carrier screening may be offered per current guidance.

If there is clinical suspicion of syphilis or exposure, refer to the syphilis guideline and seek urgent specialist advice.

Imaging

• Dating ultrasound if gestational age is uncertain; not required before 12 weeks in a low-risk pregnancy with reliable dates.
• Nuchal translucency ultrasound at 11+0 to 13+6 weeks as part of combined first trimester screening.
• Fetal morphology and placental localisation scan, usually at around 20 weeks.
• Additional scans (growth, additional monitoring) as indicated by individual risk, for example a woman with a previous perinatal death may need extra scans and monitoring.

5. Management

Antenatal care is a stepwise, longitudinal process:

Step 1: First contact / booking (by 10 weeks).

• Confirm pregnancy, establish gestational age and estimated due date.
• Perform comprehensive clinical and psychosocial assessment; identify women needing extra care.
• Check BP, BMI and urine for proteinuria.
• Provide information on fetal development, nutrition, vitamin D supplementation, exercise (including pelvic floor exercises), antenatal screening, pregnancy care, breastfeeding and available maternity supports.
• Offer and arrange antenatal screening tests; arrange early ultrasound and the fetal anomaly (morphology) scan.
• This may be spread across two appointments.

Step 2: Review of results.

• Review, discuss and record the results of all screening tests.
• Act on abnormal results: iron for anaemia, haemoglobinopathy workup for low MCV, aneuploidy pathway (NIPT then diagnostic testing) for high-risk first trimester screening, and referral or specialist advice for positive infection screens.

Step 3: Ongoing scheduled visits.

• Follow the visit frequency table above, intensifying as pregnancy progresses.
• At each visit: ask about problems and untoward symptoms, measure BP, test urine for proteinuria, and measure SFH once appropriate.
• Perform routine GDM screening at 26 to 28 weeks.

Step 4: Prevention and supplementation.

• Folic acid and iron supplementation as clinically appropriate.
• For women at increased risk of preterm pre-eclampsia, calcium supplementation may be considered; achieving a high dose (over 1000 mg/day) requires two to three tablets daily, which affects acceptability and compliance. In Australia a 600 mg tablet is available, so at least two tablets are needed.
• Offer pregnancy-related vaccinations per the Australian Immunisation Handbook.

Step 5: Group B streptococcus and intrapartum planning.

• Identify women for intrapartum antibiotic prophylaxis using the recommended risk-factor based approach where that is local policy.

Step 6: Postnatal transition.

• Plan the postnatal check at 4 to 6 weeks: review maternal recovery (lochia, mood, screen for postnatal depression, breastfeeding) and the routine baby examination (weight, length and head circumference, fontanelles, eyes including red reflex, cardiovascular examination, femoral pulses, hip examination for dislocation, testes and genitalia).

6. Australian-specific considerations

• Screening approaches follow the endorsed national and jurisdictional guidance, including the national Clinical Practice Guidelines: Antenatal Care (NHMRC-endorsed) and the ADIPS approach to GDM.
• Aboriginal and Torres Strait Islander women and Māori and Pacific Islander women face barriers to accessing culturally safe care and have higher rates of some complications; the national guidelines include a specific chapter on antenatal care for Aboriginal and Torres Strait Islander women, and culturally appropriate care is a defined standard.
• STI/BBV screening should consider at-risk groups including people under 30, people who use drugs, Aboriginal and Torres Strait Islander people, those with a past STI, contacts of an STI or blood-borne virus, people with late/limited/no antenatal care, homeless people, and those with a recent partner change, guided by local epidemiology.
• Self-collection for chlamydia (and for cervical screening via Medicare items) is available and can improve access.
• GBS management (risk-factor based) follows Queensland Clinical Guidelines where applicable; other jurisdictions may differ.
• Women with a previous perinatal loss need individualised care: number and timing of appointments, out-of-hours support, additional scans and monitoring, and sensitivity to emotional triggers such as being around other pregnant women.

Clinical pearls

• Book early. Aim for the first assessment by 10 weeks so dating, screening and pre-eclampsia risk tools are useful.
• BP + urine at every visit is the backbone of pre-eclampsia surveillance; never skip it.
• A low MCV on the FBC is your prompt to pursue haemoglobinopathy evaluation and exclude iron deficiency with ferritin.
• HIV, syphilis and hepatitis B are routine, not risk-based, components of the antenatal screen; offer chlamydia to everyone under 30 and to all ages in high-prevalence areas.
• Aneuploidy pathway: combined first trimester screening → NIPT if high risk → diagnostic testing (CVS/amniocentesis) if NIPT high probability.