Key Diagnostics and Screenings at 28 Weeks Gestation
At 28 weeks gestation, essential screenings include gestational diabetes testing, fetal growth assessment, blood pressure monitoring, and assessment for preeclampsia. These screenings are critical for detecting complications that could affect maternal and fetal outcomes.
Gestational Diabetes Screening
- Screening for gestational diabetes should be performed between 24-28 weeks gestation for all pregnant women not previously diagnosed with diabetes 1
- Either one-step or two-step protocol may be used:
- One-step: 75g oral glucose tolerance test
- Two-step: 50g glucose challenge test followed by 100g 3-hour oral glucose tolerance test if screening is abnormal 1
- Blood tests including hemoglobin, platelet count, liver transaminases, uric acid, and creatinine should be performed at 28 weeks as a minimum 1
Fetal Growth Assessment
- Ultrasound assessment for fetal growth should be performed at 28 weeks, particularly in high-risk pregnancies 1
- Key measurements include:
- Head circumference (HC)
- Abdominal circumference (AC)
- Femur length (FL)
- Estimated fetal weight (EFW) calculation 2
- Growth scans at 28-32 weeks are particularly important for detecting late-onset fetal growth restriction in women with obesity 1
Antenatal Fetal Surveillance
- Initiation of antepartum fetal surveillance at 32-34 weeks for women with pregestational diabetes 1
- For pregnancies with fetal growth restriction (FGR), weekly umbilical artery Doppler assessment should be performed 1
- More frequent monitoring (2-3 times weekly) is recommended if abnormal umbilical artery Doppler findings are detected 1
Blood Pressure and Preeclampsia Screening
- Blood pressure measurement to detect hypertensive disorders
- Urinalysis for proteinuria to screen for preeclampsia 1
- Women with hypertension should be closely monitored for development of preeclampsia with more frequent visits 1
Additional Screenings for High-Risk Pregnancies
For Women with Obesity:
- Consider growth scan at 28-32 weeks to aid in detection of late-onset fetal growth restriction 1
- Assessment for excessive or inadequate gestational weight gain 1
For Women with Pregestational Diabetes:
- Low-dose aspirin 81 mg daily (should have been started between 12-28 weeks, optimally before 16 weeks) 1
- Monitoring for diabetic complications and vascular disease 1
For Women with Previous Bariatric Surgery:
- Serum indices checked every 3 months: full blood count, serum ferritin, iron studies, serum folate, serum vitamin B12 1
- Additional monitoring of serum vitamin E, zinc, copper, and selenium 1
For Women with Suspected Placenta Accreta:
- Follow-up ultrasound assessment with Doppler studies if previously identified 1
Common Pitfalls and Caveats
Failure to detect fetal growth restriction: Ensure proper measurement techniques for accurate biometry and estimated fetal weight calculation.
Missing gestational diabetes: Ensure proper timing of screening between 24-28 weeks; don't delay beyond this window.
Inadequate monitoring of high-risk pregnancies: Women with risk factors (obesity, hypertension, diabetes) require more intensive monitoring starting at 28 weeks.
Overlooking nutritional deficiencies: Particularly in women with bariatric surgery history, nutritional monitoring is essential at this stage.
Inconsistent dating: Ensure gestational age was accurately established in early pregnancy to properly interpret all screening results at 28 weeks 3.
By implementing these key screenings at 28 weeks gestation, clinicians can identify potential complications early and intervene appropriately to improve maternal and fetal outcomes.