Prenatal Screening

First Trimester (0–13 Weeks)

Initial Prenatal Labs (First Visit)

• Blood type and Rh factor

• Antibody screen

• CBC (hemoglobin/hematocrit)

• Rubella immunity

• HIV

• Hepatitis B and C

• Syphilis (RPR/VDRL)

• Chlamydia and Gonorrhea

• Urinalysis and urine culture

Urine Culture (12–16 Weeks or First Visit)

• Screen for asymptomatic bacteriuria

• No repeat screening needed in low-risk patients if negative

First Trimester Genetic Screening (11–13 Weeks)

• ↓ Low PAPP-A (Pregnancy-Associated Plasma Protein A) = increased risk for chromosomal abnormalities (especially Down syndrome)

• ↑ High hCG

• ↑ Increased thickness Nuchal Translucency Ultrasound (11–13 Weeks)= increased risk for chromosomal abnormalities (Down syndrome, trisomy 18)

= increased risk for Down syndrome

Cell-Free DNA (cfDNA) Screening (9–10 Weeks or Later)

Screens for:

1. Down syndrome (Trisomy 21)

2. Trisomy 18

3. Trisomy 13

4. Sex chromosome abnormalities

5. Fetal sex

Important:

• Highly sensitive screening test

• NOT diagnostic

• Abnormal results require:

  • Chorionic Villus Sampling (CVS)

  • Amniocentesis

Carrier Screening

Based on family history or ethnicity:

• Cystic fibrosis

• Sickle cell disease

• Tay-Sachs disease

Second Trimester (14–27 Weeks)

Quad Screen (15–22 Weeks; best at 16–18 Weeks)

1. AFP (Alpha-Fetoprotein)

• ↑ High = Neural tube defects (spina bifida)

• ↓ Low = Down syndrome

2. hCG

• ↑ High = Down syndrome

• ↓ Low = Trisomy 18

3. Unconjugated Estriol (uE3)

• ↓ Low = Down syndrome or Trisomy 18

4. Inhibin A

• ↑ High = Down syndrome

Down Syndrome Pattern:

• ↓ AFP

• ↑ hCG

• ↓ Estriol

• ↑ Inhibin A

Mnemonic:
Down = "Low High Low High"
(AFP ↓, hCG ↑, Estriol ↓, Inhibin A ↑)

Anatomy Scan (18–23 Weeks)

Evaluates:

• Fetal anatomy

• Growth and development

• Placental location

• Amniotic fluid

• Fetal sex (often identified)

Rh-Negative Patients

• Antibody screen at first visit

• Repeat screen before RhoGAM administration

• RhoGAM given at 28 weeks (7m)

Gestational Diabetes Screening (24–28 Weeks)

• 1-hour glucose tolerance test

• Universal screening for all pregnant patients

Third Trimester (28–40 Weeks)

Repeat Labs

• Hemoglobin/Hematocrit (anemia screening)

• Repeat STI screening if high risk

Group B Streptococcus (GBS) Screening (36–37 Weeks)

• Vaginal/rectal culture

GBS Positive:

• Administer IV penicillin during labor

• Prevents neonatal infection

High-Yield NCLEX Pearls

Down Syndrome Markers

• ↓ PAPP-A

• ↑ hCG

• ↑ Nuchal translucency

• Quad screen: ↓ AFP, ↑ hCG, ↓ Estriol, ↑ Inhibin A

Neural Tube Defects

• ↑ AFP

• Prevent with folic acid supplementation

Rh-Negative Mom

• RhoGAM at 28 weeks (7m) and after delivery if infant is Rh-positive

Gestational Diabetes

• Screen at 24–28 weeks

GBS

• Screen at 36–37 weeks

• Treat during labor if positive

Pregnancy Screening Timeline