Are We Testing for Gestational Diabetes Too Late?

A new study shows that babies are already showing the effects of gestational diabetes by the time expectant moms are tested for it. So are we testing too late?

Are Gestational Diabetes Screenings Happening Too Late? Theeradech Sanin/Shutterstock

No one likes the glucose tolerance test—having to chug down that nasty orange drink, and hoping there are no side effects. Unfortunately, screening for high blood sugar is a necessity in pregnancy, as gestational diabetes mellitus (GDM) can cause problems ranging from stillbirth to childhood obesity. But a new study published in journal Diabetes Care suggests that unborn babies are showing the effects of GDM before expectant mothers are even tested for it, throwing the screening's relevance into question. Should pregnant women be tested even earlier?

Diagnosis after baby is already affected

Researchers looked at data from over 4,000 pregnant women to measure baby's growth, as large size is an indicator of gestational diabetes, and compared that info to the 171 moms who actually developed GDM later on. They also looked at which women were obese, another risk factor for GDM. "Gestational diabetes and obesity were both associated with accelerated growth of the [baby's] abdomen between 20 and 28 weeks," study author Gordon Smith, M.D., Ph.D., the head of the department of obstetrics and gynecology at the University of Cambridge in the UK, tells Fit Pregnancy. "In relation to gestational diabetes, measurements were normal at 20 weeks, but were large by 28 weeks. Women who were both obese and had a diagnosis of gestational diabetes were almost five times more likely to have a baby with a large abdominal measurement at 28 weeks."

Because GDM wasn't actually diagnosed in the women until 28 weeks, "the effects of gestational diabetes [are] already present at the time we normally make the diagnosis," Dr. Smith says. Although diagnosis at any time in the pregnancy can help prepare for complications that might arise, the study shows finding out late can't help to prevent the disease's effects on baby in the first place. "The current guidelines in the USA and UK are to screen at some point between 24 and 28 weeks," Dr. Smith says. So, "one response to the current findings might be to screen as close as possible to 24 weeks. Screening prior to 24 weeks might also result in better outcomes."

Although the study would seem to suggest testing women even earlier than the current guidelines, Smith says that approach is not without its own issues. "Screening too early could also cause problems—if women are only tested once in pregnancy, it is possible that cases of gestational diabetes may be missed if the screening is carried out too early," he says. "This is because gestational diabetes tends to get worse as the pregnancy goes on. Mild disease may be missed by testing too early."

When to test?

More studies are needed to figure out exactly when is the best time to test for GDM in order to catch problems before baby begins to show the effects, but while still being able to identify the greatest number of cases. "Screening prior to 24 weeks might result in better outcomes," Dr. Smith says. "However, this would require trials to prove that such an approach was beneficial, prior to implementing earlier screening. Ultimately, two-stage screening may be required." Drinking that orange stuff twice? Not exactly fun, but it might be necessary.

Why would an earlier diagnosis be better? Earlier treatment (including special meal planning, physical activity and maybe even insulin injections), may help avoid the production of excess sugar that causes baby to grow too large. "The sugar crosses the placenta, resulting in extra 'fuel' for growth," Smith says. And bigger is not always better. "Being big places a baby at increased risk of complications in the short term including stillbirth and obstructed labor, leading to higher rates of cesarean section and difficult delivery," Dr. Smith says. "In particular, we are concerned about shoulder dystocia, where there is a delay following delivery of the baby's head due to excessive size of the body. This can cause trauma and oxygen deprivation."

In addition, GDM has been linked with problems for children later on. "The main long-term problem is that big babies where the mother had gestational diabetes are at increased risk of childhood obesity," Dr. Smith says. Other research has shown that screening and treatment for GDM do not reduce the rate of childhood obesity, but this study might explain why—by the time screening and treatment occurs, the baby's future chances of obesity have already been raised.

For now, Smith advises that pregnant women be screened on the earlier side of the testing window of 24 to 28 weeks, especially if they are obese or have other risk factors for GDM. "If they cannot make a 28 week appointment, the test should be done earlier—although not before 24 weeks—rather than later," he says. Plus, at-risk women (and everyone, really), would benefit from a healthy diet. "This involves not eating excessive quantities of simple carbohydrates, controlling portion sizes, eating plentiful fresh fruit and vegetables, and remaining active during the pregnancy," Dr. Smith says.