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Question

Difficulty: MediumNormal Pregnancy and Prenatal Care

A clinic nurse is preparing an educational timeline chart for patients beginning their prenatal care. Match each routine obstetrical screening test or intervention to the precise gestational age window during which it is standardly recommended for an uncomplicated pregnancy.

  • Cell-free fetal DNA (cfDNA) screeningCan be performed any time ≥\ge 10 weeks gestation
  • Maternal serum alpha-fetoprotein (MSAFP) screeningOptimally performed between 15 and 22 weeks gestation
  • 50-g 1-hour oral glucose challenge testStandardly performed between 24 and 28 weeks gestation
  • Routine prophylactic anti-D immune globulinTypically administered at 28 weeks gestation
  • Group B Streptococcus (GBS) rectovaginal culturePerformed between 36 0/7 and 37 6/7 weeks gestation

Answer

cfDNA is performed at ≥\ge 10 weeks; MSAFP at 15 to 22 weeks; the glucose challenge test at 24 to 28 weeks; anti-D immune globulin at 28 weeks; and GBS screening at 36 0/7 to 37 6/7 weeks.
A comprehensive understanding of prenatal care requires knowing the specific physiological rationales that dictate the timing of each intervention: cfDNA at ≥\ge 10 weeks (fetal fraction viability), MSAFP at 15-22 weeks (neural tube defect detection), GDM screening at 24-28 weeks (peak insulin resistance), RhoGAM at 28 weeks (standardized alloimmunization prevention), and GBS at 36-37 weeks (validity of colonization status at delivery).

Step-by-Step Solution

1
Identify first-trimester screening options.
cfDNA screening is indicated starting at 10 weeks gestation when fetal DNA fraction is high enough for accurate aneuploidy analysis.
Ensures early detection of chromosomal abnormalities.
2
Determine early second-trimester screening milestones.
MSAFP screening is assigned to the 15 to 22-week window.
This is the precise physiologic window where maternal serum levels optimally reflect the risk of fetal open neural tube defects.
3
Assign late second-trimester metabolic and immunologic interventions.
The 50-g glucose challenge test is performed at 24 to 28 weeks, and anti-D immune globulin is administered at 28 weeks.
Placental lactogen induces maximum insulin resistance at 24-28 weeks, and 28 weeks is the standardized time to prevent third-trimester Rh alloimmunization.
4
Identify late third-trimester pre-labor infectious screening.
GBS rectovaginal culture is matched to 36 0/7 to 37 6/7 weeks gestation.
Testing must occur within 5 weeks of expected delivery to ensure the culture result accurately reflects colonization status during labor.

Key Concept

Routine Prenatal Screening Timeline
Estimated Time:1m 30s
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Topics

Normal Pregnancy and Prenatal Care

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