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Difficulty: EasyNormal Pregnancy and Prenatal Care

Match each gestational age window or prenatal visit timing with the most appropriate routine screening test indicated at that time for an average-risk, uncomplicated pregnancy.

  • Initial prenatal visit (First Trimester)ABO blood typing, Rh(D) status, and antibody screen
  • 15 to 22 weeks gestationMaternal serum alpha-fetoprotein (MSAFP) / Quadruple marker screen
  • 24 to 28 weeks gestation1-hour 50-g oral glucose challenge test
  • 35 to 37 weeks gestationRectovaginal culture for Group B Streptococcus (GBS)

Answer

The initial visit matches with ABO/Rh typing; 15-22 weeks matches with the MSAFP/Quad screen; 24-28 weeks matches with the 1-hour glucose challenge test; and 35-37 weeks matches with the GBS rectovaginal culture.
Each routine prenatal screening test has a rigorously defined optimal window based on fetal development, maternal physiological adaptations (like insulin resistance), and the temporal proximity required for safe delivery management.

Step-by-Step Solution

1
Determine the required baseline laboratory tests for early pregnancy.
The initial prenatal visit (first trimester) includes checking ABO blood type and Rh(D) status to plan for potential anti-D immune globulin administration.
Early identification of Rh-negative mothers is critical to prevent hemolytic disease of the fetus and newborn.
2
Identify the screening window for structural and genetic abnormalities.
The 15 to 22-week window is appropriate for the quadruple marker screen (including MSAFP).
Analyte levels during this specific gestational timeframe offer the highest sensitivity for detecting open neural tube defects and common aneuploidies.
3
Identify when maternal metabolic changes necessitate diabetes screening.
The 24 to 28-week window corresponds to the 1-hour 50-g oral glucose challenge test.
Placental hormones, primarily human placental lactogen, increase insulin resistance significantly by late second trimester, making this the optimal time to detect gestational diabetes.
4
Determine the timing for infectious disease screening related to delivery.
The 35 to 37-week window requires rectovaginal screening for Group B Streptococcus.
Because GBS flora can change over time, testing must occur within 5 weeks of expected delivery to accurately guide intrapartum prophylaxis.

Key Concept

Routine Prenatal Screening Schedule
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Topics

Normal Pregnancy and Prenatal Care

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