What testing and screening should be completed on a 28-year-old female at 28 weeks gestation with no prior prenatal care?

Initial Testing and Screening for a 28-Year-Old at 28 Weeks Gestation with No Prior Prenatal Care

This patient requires immediate comprehensive laboratory testing, infectious disease screening, aneuploidy assessment, anatomic ultrasound evaluation, and glucose screening to identify high-risk conditions and optimize maternal-fetal outcomes despite the delayed presentation.

Immediate Laboratory Testing

Essential Baseline Tests

• Complete blood count to assess for anemia, which is common in pregnancy and requires treatment 1
• Blood type and Rh screen to identify Rh-negative status requiring RhoGAM administration and detect antibodies that could cause hemolytic disease 1, 2
• Urinalysis and urine culture to screen for asymptomatic bacteriuria 2
• Serum creatinine and urinary protein assessment (albumin-to-creatinine ratio or 24-hour collection) to evaluate renal function, as protein excretion ≥190 mg/24h increases risk for hypertensive disorders 3

Infectious Disease Screening

• Rubella immunity status to determine susceptibility and need for postpartum vaccination 1, 2
• Syphilis screening (RPR or VDRL) as untreated syphilis causes significant fetal morbidity 1, 2
• Hepatitis B surface antigen to identify chronic infection and prevent vertical transmission 1, 2
• HIV testing to initiate antiretroviral therapy if positive and reduce transmission risk 1, 2
• Gonorrhea and chlamydia screening via cervical or urine testing 1, 2
• Hepatitis C testing should be considered given the current epidemiology 2

Metabolic and Endocrine Assessment

• Thyroid stimulating hormone (TSH) and free thyroxine, particularly important as hypothyroidism requires medication adjustment during pregnancy 3, 1
• Hemoglobin A1C if diabetes risk factors present or if not previously screened 3

Glucose Screening

Immediate glucose testing is required at this visit given the patient's late presentation at 28 weeks gestation 1. Perform either:

• One-step approach: 75-gram oral glucose tolerance test, or
• Two-step approach: 50-gram glucose challenge test followed by 100-gram oral glucose tolerance test if abnormal

High-risk patients (obesity, previous gestational diabetes, strong family history) who present late should undergo immediate testing rather than waiting, as they may have had undiagnosed pre-existing diabetes 1.

Ultrasound Evaluation

Comprehensive Anatomic Survey

A detailed anatomic ultrasound is essential at 28 weeks to evaluate for:

• Fetal growth and estimated fetal weight to assess for intrauterine growth restriction or macrosomia 3
• Amniotic fluid volume (oligohydramnios or polyhydramnios) 3
• Placental location and appearance to identify placenta previa or other abnormalities 3
• Comprehensive fetal anatomy including:
  • Cardiac four-chamber view and outflow tracts 3
  • Cranial anatomy and measurement of nuchal fold thickness 3
  • Spine for neural tube defects 3
  • Abdominal wall, kidneys, and bladder 3
  • Extremities for skeletal abnormalities 3

Soft Marker Assessment

If isolated soft markers are identified (echogenic intracardiac focus, choroid plexus cysts, echogenic bowel, urinary tract dilation, shortened long bones, thickened nuchal fold, or absent/hypoplastic nasal bone), aneuploidy screening should be offered via cell-free DNA testing or quad screen given the lack of prior screening 3.

Aneuploidy Screening

Cell-free DNA (cfDNA) screening should be offered immediately as the patient has had no prior aneuploidy assessment 3, 1. While typically performed earlier in pregnancy, cfDNA can still provide valuable information at 28 weeks. Alternatively, if cfDNA is unavailable or cost-prohibitive, quad screen can be performed, though its detection rate is lower 3.

Genetic counseling should be offered to discuss:

• Age-related aneuploidy risk (though at 28 years, risk is relatively low) 2
• Family history of genetic disorders 2
• Ethnic background for carrier screening (cystic fibrosis, hemoglobinopathies, Tay-Sachs, etc.) 2

Additional Assessments

Blood Pressure and Hypertensive Disorder Screening

• Blood pressure measurement at this visit and ongoing monitoring, as hypertensive disorders can develop in the third trimester 2
• Assess for symptoms of preeclampsia (headache, visual changes, right upper quadrant pain, edema) 3

Medication Review

• Identify and discontinue FDA pregnancy category X medications immediately 1, 2
• Review category D medications and continue only if maternal benefits clearly outweigh fetal risks 1, 2
• Specifically discontinue ACE inhibitors or angiotensin receptor blockers if used for hypertension 3

Substance Use Screening

• Screen for tobacco, alcohol, and illicit drug use using validated tools such as CAGE or T-ACE questionnaires 1, 2
• Provide smoking cessation counseling using the five A's approach (Ask, Advise, Assess, Assist, Arrange) 2
• Counsel complete abstinence from alcohol 2

Nutritional Assessment

• Assess body mass index and weight gain pattern 2
• Initiate prenatal vitamins with folic acid if not already taking, though neural tube defect prevention benefit is primarily in first trimester 1, 2
• Evaluate dietary intake and nutritional deficiencies 2

Psychosocial Screening

• Screen for depression and anxiety using validated instruments 1, 2
• Screen for intimate partner violence and provide appropriate referrals if identified 2
• Assess for major psychosocial stressors and support systems 2

Immunization Status

• Review immunization history and administer indicated vaccines 2:
  • Tdap vaccine (ideally between 27-36 weeks gestation, so can be given at this visit)
  • Influenza vaccine if during flu season
  • Do not administer live vaccines (MMR, varicella) during pregnancy 2

Common Pitfalls to Avoid

• Do not delay glucose screening until a later visit—it should be performed at this initial encounter given the 28-week gestational age 1
• Do not assume normal anatomy without ultrasound confirmation, as many anomalies can still be detected at 28 weeks 3
• Do not skip infectious disease screening even if the patient appears low-risk, as these infections have significant implications for delivery planning and neonatal care 1, 2
• Do not overlook the need for Rh immune globulin if the patient is Rh-negative and has not received it at 28 weeks 1

Ongoing Care Planning

Establish frequent prenatal visits (every 2 weeks until 36 weeks, then weekly) to compensate for missed early care 2. Arrange referral to maternal-fetal medicine if high-risk conditions are identified, including pre-existing diabetes, chronic hypertension, fetal anomalies, or evidence of intrauterine growth restriction 2.