When is the glucose test done for gestational diabetes?

What does the evidence say about gestational diabetes glucose screening test timing during pregnancy?

1. Universal screening for gestational diabetes is recommended for everyone between 24 and 28 weeks of pregnancy. 1
2. Practices use one of two protocols: a single 75-gram, 2-hour test, or a 50-gram screening test followed by a longer 100-gram, 3-hour test only if that first result comes back high. 2
3. ACOG guidance summarized in StatPearls describes early testing for type 2 diabetes at the initial prenatal visit in patients with obesity plus another risk factor, such as prior gestational diabetes or a first-degree relative with diabetes. Early testing is distinct from routine gestational diabetes screening. 1
4. Evidence that earlier screening actually improves outcomes is still limited, and one review found early screening did not clearly improve results in patients with obesity, which is part of why most guidelines still anchor routine testing at 24 to 28 weeks. 3
5. A confirmatory 3-hour test follows an abnormal 1-hour result in the two-step protocol, and the usual criteria for gestational diabetes require at least two of the four checked values to land at or above the threshold. 4

Is gestational diabetes glucose screening test timing safe in each trimester?

• First trimester. Early blood-sugar testing in a higher-risk pregnancy may look for previously unrecognized type 2 diabetes. It serves a different purpose from routine gestational diabetes screening later in pregnancy; ask your provider how your medical history affects the testing plan.
• Second trimester. Routine screening for everyone else happens between 24 and 28 weeks, using either a single 75-gram test or a 50-gram challenge that's followed by a longer confirmatory test only if that first result runs high.
• Third trimester. The routine 24-to-28-week screening window extends into the start of the third trimester. If testing was missed or new concerns arise, your provider can arrange an appropriate assessment rather than assuming the opportunity has passed.