Background:

In a 2003 evidence report, the United States Preventive Services Task Force (USPSTF) concluded that the scientific evidence was insufficient to advise for or against routine screening for gestational diabetes mellitus (GDM) in all pregnant women. The 2003 review did not include evidence pertaining to GDM screening prior to 24 weeks gestation. As the prevalence of women at high risk for type 2 diabetes and GDM has continued to increase dramatically over the intervening years, the issue of early screening has taken on greater importance.

Purpose:

This review identifies and evaluates new evidence since the prior review on the risks and benefits of GDM screening at 24 weeks or later; it also newly reviews all of the available evidence pertaining to GDM screening prior to 24 weeks.

Data Sources:

We conducted five database searches of MEDLINE^®, Cochrane Central Registry of Controlled Trials, Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effects, Health Technology Assessment, and National Institute for Health and Clinical Excellence from 2000 to September 2006, supplemented by a search for screening prior to 24 weeks gestation from 1966-99. Searches were also supplemented with recommendations from outside experts and reviews of bibliographies of other relevant articles and systematic reviews. We dual-reviewed all citations in the 2003 Evidence Synthesis for inclusion in this review.

Study Selection:

In conjunction with USPSTF members and with Agency for Healthcare Research and Quality staff, we developed and refined an analytic framework and five key questions (KQ). For assessing potential benefit of GDM screening and treatment, we included only randomized trials that used the standard, currently accepted one-step and two-step diagnostic criteria to evaluate screening and treatment of GDM. Study design and criteria were less stringent for considering potential harms. Using inclusion/exclusion criteria for each question, two investigators dual-reviewed 1403 abstracts and 277 potentially included articles. Of the potentially included articles, 90 were excluded for study design and 12 for poor quality, and the remainder for other reasons.

Data Extraction:

We abstracted, critically appraised, and synthesized 13 total articles meeting criteria for the five KQs. Abstracted elements were arrayed in evidence tables, using criteria specific to each KQ.

Data Synthesis and Results:

The best new evidence is a good-quality randomized controlled trial (RCT) that evaluated the maternal and neonatal outcomes for 1,000 pregnancies in which mild GDM was diagnosed between 24–34 weeks gestation and treated, compared to outcomes for pregnancies in which mild GDM was diagnosed but not treated. With treatment, there was a statistically significant reduction in the composite neonatal outcome of any serious perinatal complication (Adjusted RR 0.33 [95 percent CI 0.14–0.75]). Serious perinatal complications was defined as any of the following: death, shoulder dystocia, bone fracture, and nerve palsy. The absolute rates of these individual perinatal outcomes were also reported in the paper, but could not be compared between groups due to no events for death, bone fracture, or nerve palsy in the treatment group. Overall, there were seven infants with serious perinatal complications in the treatment group (all shoulder dystocia), compared to 23 infants with 25 serious perinatal complications in the non-treated group (five deaths, one fractured humerus, three nerve palsies, and 16 shoulder dystocia). Shoulder dystocia was not a specified health outcome for this evidence review. The remaining components in the composite outcome (neonatal death, fracture, nerve palsy) were health outcomes specified by the Task Force for this review. The causes of the five deaths in the untreated group were: two stillbirths (unexplained intrauterine deaths at term of appropriately grown infants), one stillbirth at 35 weeks gestation associated with pre-eclampsia and intrauterine growth restriction, one infant death from asphyxia during labor without antepartum hemorrhage, and one death from a lethal congenital anomaly.

Treatment of GDM also reduced the risk of maternal pregnancy-induced hypertension (Adjusted RR 0.70 [0.51–0.95]). There was no evidence of harm to mother or infant with treatment in this study. In a sub-set of participants who responded to a post-partum questionnaire, mothers treated for GDM were significantly less depressed and reported a trend towards better quality-of-life at 3 months post-partum; these post-partum data may have some limitations.

Of five treatment comparison trials, two achieved improved glycemic control with intensified management of different types (postprandial monitoring and four times daily insulin) and both found significant reductions in several perinatal complications (a combined outcome for perinatal morbidity in one study, hyperbilirubinemia, and macrosomia). These improved outcomes occurred without evidence of harms from significant maternal hypoglycemia with treatment. The remaining three treatment-comparison trials did not differ in glycemic control achieved and outcomes were similar. Finally, available evidence suggests that diagnosis and treatment of GDM does not worsen quality-of-life except possibly transiently for the first few weeks after diagnosis. As early as 6 weeks after diagnosis, women treated for GDM may have better self-rated quality-of-life.

Limitations:

We found no evidence base for trials of screening programs to test screened versus unscreened populations. However, both current clinical practice patterns for GDM and ethical constraints on research in human subjects would now likely preclude such a study in the US. Thus, the available evidence base comprises studies in only screen-detected populations.

Evaluating the potential benefit and harms of screening and treatment of GDM is limited by lack of a consistent standard for screening or diagnosis and the need to consider multiple potential outcomes that are not unique to GDM.

Little information is available on harms of treatment—these are relatively rare outcomes and may not be evident in trials.

While antepartum surveillance was specifically restricted from the scope of this review by the Task Force, it is possible that increased antepartum surveillance of women diagnosed with GDM could result in harms that were not evaluated with this review.

Conclusions:

We found limited evidence to evaluate early screening for GDM prior to 24 weeks gestation, the purpose of which would be to detect previously unrecognized diabetes (GDM is defined as onset or first recognition of diabetes during pregnancy). Therefore, more research is needed before this question can be evaluated.

A recent good-quality randomized controlled trial reported that treatment of screen-detected women with mild GDM diagnosed after 24 weeks gestation reduces both maternal and composite neonatal health outcomes, without apparent harm—as reported in this RCT and in several other observational studies.