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Difficulty: EasyNormal Pregnancy and Prenatal Care

Match each gestational age timeline during an uncomplicated pregnancy with the most appropriate routine maternal or fetal screening test.

  • Initial prenatal visit (typically 8 to 10 weeks gestation)Blood type, Rh(D) status, atypical antibody screen, and routine infectious disease panel
  • 15 to 20 weeks gestationMaternal serum alpha-fetoprotein (MSAFP) screening for open neural tube defects
  • 24 to 28 weeks gestationOne-hour 50-g oral glucose challenge test for gestational diabetes screening
  • 36 to 37 6/7 weeks gestationRectovaginal swab for Group B Streptococcus (GBS) culture

Answer

Initial prenatal visit matches with Blood type and infectious disease panel; 15 to 20 weeks matches with MSAFP screening; 24 to 28 weeks matches with 1-hour oral glucose challenge test; 36 to 37 6/7 weeks matches with Rectovaginal swab for GBS culture.
Each gestational age milestone has specific, evidence-based routine screening tests. The initial visit establishes maternal baseline health and infectious risks. The early second trimester (15-20 weeks) is the dedicated window for MSAFP/quadruple screening to detect structural anomalies and aneuploidy. The late second trimester (24-28 weeks) coincides with peak insulin resistance, making it the appropriate time for gestational diabetes screening and a repeat blood count. The late third trimester (36-37 6/7 weeks) is the optimal time for GBS screening to ensure results accurately reflect colonization status at the onset of labor.

Step-by-Step Solution

1
Identify the standard labs indicated at the beginning of prenatal care.
The initial prenatal visit requires baseline labs including blood type, Rh status, and infectious disease screening.
Early identification of maternal infectious diseases or Rh-negative status allows for prompt intervention to prevent vertical transmission or alloimmunization.
2
Determine the optimal window for maternal serum alpha-fetoprotein (MSAFP) screening.
MSAFP is optimally drawn between 15 and 20 weeks gestation.
This window provides the most accurate assessment of the risk for fetal open neural tube defects.
3
Identify the timing for universal gestational diabetes screening.
The 1-hour oral glucose challenge test is performed between 24 and 28 weeks.
Maternal insulin resistance peaks in the late second and third trimesters due to placental hormone production, making this the optimal screening window.
4
Determine the correct timing for Group B Streptococcus (GBS) screening.
A rectovaginal swab for GBS culture is performed between 36 0/7 and 37 6/7 weeks gestation.
Screening at this time accurately predicts GBS colonization status at the time of delivery, guiding the need for intrapartum antibiotic prophylaxis.

Key Concept

Routine prenatal screening timeline and gestational age milestones
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Topics

Normal Pregnancy and Prenatal Care

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