US Task Force: Screen for Diabetes After 24 Weeks' Gestation

Marlene Busko

January 13, 2014

Following a draft statement issued last May, the US Preventive Services Task Force has released a final statement saying that there is sufficient evidence to recommend screening for gestational diabetes mellitus after 24 weeks of pregnancy, but insufficient evidence to recommend earlier screening. The guidance is published online January 13 in the Annals of Internal Medicine.

Apart from a few clarifications in wording to address feedback from the public, the recommendations remain the same as in last year's draft, former task-force member Wanda K. Nicholson, MD, from the University of North Carolina at Chapel Hill, told Medscape Medical News.

This statement updates their 2008 paper. "In 2008 we had an 'I statement'; we thought there was insufficient evidence to clearly say that benefits [of screening for gestational diabetes after 24 weeks] outweighed harms," Dr. Nicholson explained.

"We now have had some large, very well-done clinical trials that have filled those gaps in evidence…[and] clearly showed a benefit for mothers and babies with screening vs not screening" after 24 weeks, "so this is now a 'B recommendation.' But there was insufficient evidence to clearly support earlier screening," she said.

Stronger Evidence for Screening

It is important to screen for and treat gestational diabetes, which affects a fair number of women, the authors write. The prevalence of gestational diabetes in the United States ranges from 1% to 25%. Not only do these women have an increased risk for pregnancy complications, but up to 60% go on to develop type 2 diabetes within 5 to 15 years of delivery. When gestational diabetes is diagnosed and then blood glucose levels are controlled, women can decrease risks for pregnancy complications.

The task force aimed to review existing clinical-trial evidence to determine whether the benefits of screening for gestational diabetes at 2 time points — before or after 24 weeks of gestation — outweighed the harms.

Overall, the evidence showed that screening pregnant mothers for gestational diabetes after 24 weeks — generally between 24 and 28 weeks — and treating any detected diabetes can significantly reduce the risk for preeclampsia for the mother and for macrosomia or shoulder dystocia at birth for the baby, Dr. Nicholson said. Any harms from screening for and treating gestational diabetes were small.

Women at high risk for gestational diabetes include those who are obese, older, have had previous gestational diabetes, have a family history of diabetes, or belong to an ethnic group with an increased risk of developing type 2 diabetes (Hispanic, Native American, South or East Asian, African American, or Pacific Island descent).

These women are commonly screened earlier than 24 weeks. Physicians need to use their clinical judgment to determine whether an individual patient who is at high risk for gestational diabetes should be screened earlier, the group writes.

And doctors need to recognize that all women of childbearing age — even if they are nowhere near considering pregnancy — need to adopt healthy habits such as eating a healthful diet and being physically active to attain an optimal weight and reduce the risk of potential future gestational diabetes, Dr. Nicholson stressed.

Evidence Came From 1-Step and 2-Step Diagnoses

The recommendation statement examined evidence from studies that used the 2-step approach for screening for gestational diabetes, commonly used in the United States, as well as the 1-step approach, commonly used in Europe.

In the 2-step approach, a patient first has a nonfasting 50-g oral glucose challenge test. If her blood glucose level is at or above a certain threshold, she has a fasting oral glucose tolerance test, in which gestational diabetes is diagnosed based on blood glucose levels 1, 2, and 3 hours after ingesting 100 g of glucose.

In a 1-step approach, a patient who is fasting ingests 75 g of glucose, and gestational diabetes is diagnosed if blood glucose levels 1 and 2 hours later reach certain target levels.

As reported by Medscape Medical News, different organizations have varying stances on whether to recommend the 1- or 2-step approach for screening for gestational diabetes.

The 1-step approach uses a lower level of blood glucose to diagnose gestational diabetes and is a subject of contention, with critics saying that it will increase the frequency of diagnosis of gestational diabetes 2- to 3-fold. It also requires women to fast for at least 8 hours beforehand.

In March 2013, a National Institutes of Health panel came out in favor of keeping the 2-step approach. In July, the American College of Obstetrics and Gynecologists (ACOG) issued a practice bulletin also supporting this stance. But in November, the Endocrine Society issued a new clinical-practice guideline advocating a 1-step approach. Then just last month, the American Diabetes Association, which had previously supported a 1-step approach, issued a new recommendation stating that there is not enough evidence to favor switching to this strategy, so either approach is acceptable.

"The screening strategy — whether you use the 1-step or 2-step [approach] — we didn't address that as part of the evidence we reviewed," said Dr. Nicholson. "We focused on [answering the question] 'Does screening for gestational diabetes mellitus make a difference?' The answer was clearly 'Yes.' "

Ann Intern Med. Published online January 13, 2014. Article


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