A pregnant woman at 26 weeks gestation asks which diagnostic test is most appropriate to order at this time. Which test should be performed?

• A. VDRL
• B. Amniocentesis
• C. Maternal serum alpha-fetoprotein
• D. 1-hour post-Glucola glucose screening

Answer: (D)

Screening for gestational diabetes in the late second trimester is the main idea here. Around 24–28 weeks, the standard approach is to perform a one-hour glucose challenge test with a 50-gram oral glucose load. It’s a screening test (nonfasting) to identify women who may have impaired glucose tolerance; if this test is elevated, a formal diagnostic glucose tolerance test is pursued. This timing and test are chosen because detecting maternal hyperglycemia before delivery helps reduce risks for the baby and mother.

Other options aren’t as appropriate at this time. A VDRL is a syphilis screen that can be done earlier in pregnancy and isn’t specifically timed to 26 weeks. Maternal serum alpha-fetoprotein is used primarily for neural tube defect screening earlier in the second trimester (roughly 15–20 weeks). Amniocentesis is an invasive diagnostic procedure reserved for when there’s a specific indication, such as abnormal screening results or another concern, and isn’t a routine test at this gestational age.