What is gestational diabetes?

We encourage you to read the beginning of the Evidence Based Birth® Signature Article on Diagnosing GDM. There, we define several important terms and explain what’s going on in the body when someone has GDM.

Gestational diabetes is a complex topic, so we reached out to experts in the field for help describing the condition. The background information in the Diagnosing GDM article will give you a basic understanding before moving on to the evidence on induction for gestational diabetes. Pre-existing diabetes (Type 1 and Type 2) are managed differently from GDM and are not covered in this article.

What problems can result from gestational diabetes?

In the Evidence Based Birth® Signature Article on Diagnosing GDM, we discuss the “Hyperglycemia and Adverse Pregnancy Outcomes” (HAPO) study in detail. This study is the most important research that has ever been done on the link between maternal blood sugar and risk of poor birth outcomes (HAPO, 2008). The key finding from the HAPO study was that the relationship between a mother’s blood sugar levels and the risk of poor birth outcomes is continuous. This means that there is no specific cutoff for risk—the risk of poor outcomes increases step-by-step with every small increase in blood sugar levels, even at levels not considered to be GDM.

The HAPO study and other studies have linked GDM to higher rates of:

(HAPO, 2008; England et al. 2009; Tobias et al. 2017; Clausen et al. 2009)

Pre-eclampsia

Fetal high blood sugar

First-time Cesarean

Premature birth

Higher birth weight/having a large baby

Shoulder dystocia or birth injury

Newborn intensive care

Newborn jaundice

Newborn low blood sugar

The mother developing diabetes and/or heart disease later in life

The baby developing excess body weight and/or diabetes later in life

How common is induction for gestational diabetes?

There is very little data on how often people with GDM are induced because of their diagnosis. In the U.S., birth certificates do not accurately track labor induction. Birth certificates also do not provide accurate info about the reasons for induction (Declercq et al. 2013; Dublin et al. 2014).

We found one retrospective study that looked at more than 330,000 births in the U.S. from 2001 to 2007 and described trends in labor induction (Dublin et al. 2014). The people in the study came from six health insurance plans, many different hospitals and regions, and represented a large and diverse population. Health insurance plan data was linked to birth certificate data in order to improve accuracy compared to using birth certificate data alone. The researchers stated that induction occurred if it was documented either in the health insurance plan records or birth certificate data. One limitation of this study is that all of the participants were insured, and less than 6% were enrolled in Medicaid, so the findings may differ for those without private insurance.

Overall, 30% of labors were induced. When they looked at reasons for induction, 59% of the labors were induced for an accepted medical reason and 41% were considered to be elective inductions. There is no official definition of elective induction, so the researchers defined an elective induction as an induction that occurred before 40 completed weeks of pregnancy without one of the listed medical indications. They did not consider a suspected big baby to be a valid medical indication.

The researchers found that diabetes (gestational diabetes or pre-existing diabetes) was the medical reason given for 10% of the medically indicated inductions. Unfortunately, the authors did not distinguish between GDM and diabetes that was present before the pregnancy, so we don’t know how many of those were specifically induction for gestational diabetes.

Does gestational diabetes always mean induction of labor?

Since people with GDM and their babies are at increased risk of pregnancy complications, some care providers encourage women with GDM to plan an early birth (usually elective induction) at or near term instead of waiting for labor to start on its own. However, it’s important that we have evidence to show that planned early birth actually benefits mothers with GDM and their babies before recommending medical induction for gestational diabetes as routine.

Evidence from randomized controlled trials

Biesty et al. (2018) published a Cochrane review in which they searched for randomized controlled trials that compared planned early birth (elective induction or Cesarean) at or near term (37 to 40 weeks’ gestation) versus expectant management for people with GDM. Unfortunately, they found only one randomized controlled trial to include in the review (Alberico et al. 2017).

Side note: In an earlier version of this Evidence Based Birth® article, we cited another trial on this topic (Kjos et al. 1993), but that study was not included in the Cochrane review because it included women with pre-existing Type 2 diabetes as well as those with GDM.

The GINEXMAL Trial

The large Alberico et al. (2017) trial (called the GINEXMAL Trial) took place at eight hospitals across Italy, Slovenia, and Israel. The participants all had GDM as diagnosed by the International Association of Diabetes and Pregnancy Study Groups (IADPSG) criteria and no other maternal or fetal medical problems. The IADPSG diagnostic criteria are described in our Signature Article on Diagnosing GDM. In the GINEXMAL trial, 214 participants were randomly assigned to an induction of labor between 38 weeks, 0 days and 39 weeks, 0 days of pregnancy (i.e., early term induction). The other 211 participants were assigned to wait for labor to start on its own until 41 weeks, 0 days, as long as no medical problems developed (i.e., expectant management). They received fetal monitoring tests twice per week until birth.

When they compared the groups at baseline (right after randomization), fewer people in the early term induction group used medication to manage their GDM, compared with those in the expectant group (56% used medication in the early term induction group versus 76% in the expectant management group). This means that the groups weren’t completely similar to begin with. However, the number of people with well-controlled blood sugar levels was the same between the groups, so the authors think it probably didn’t affect the study results (Alberico et al. 2017).

The researchers found that for babies, there were no differences between groups in the number of large babies (more than 8 pounds, 13 ounces, or 4,000 grams), or the risk of shoulder dystocia, breathing problems, low blood sugar, or intensive care. More babies in the early term induction group experienced jaundice (10% versus 4%).

For mothers, there was no difference between groups in the risk of Cesarean, birth with forceps/vacuum, postpartum hemorrhage, intensive care, or intact perineum. No deaths occurred among mothers or babies in the study.

The quality of the evidence from this study was considered low to very low because of high risk of bias (women and their care providers were not blinded). Also, the study was too small to look at differences in rare outcomes, such as death (Biesty et al. 2018). There was a small amount of crossover between groups, when people didn’t stick with their random group assignments: 11% of people assigned to early term induction were not induced as intended and 9% of people assigned to expectant management actually received an early elective induction. Regardless, the researchers concluded that the amount of crossover was not significant enough to change the results (Alberico et al. 2017).

Not surprisingly, early term induction was linked to overall lower birth weights for newborns. However, the decrease in birth weights with early term induction did not make a difference for any of the clinically important outcomes, including the number of babies more than 8 pounds, 13 ounces (4,000 grams), Cesareans, or shoulder dystocia. In the study, shoulder dystocia occurred in three births in the early induction group and one birth in the expectant management group and this difference was not significant. All four cases of shoulder dystocia were resolved without any problems.

In theory, a reduction in birth weights could reduce the risk of shoulder dystocia, but since shoulder dystocia was so infrequent, a larger randomized trial would be needed to study this outcome. Also, it would likely take a very large number of women with GDM to ‘treat’ with early term induction in order to prevent one event of shoulder dystocia. In the same way, it would take a very large number of women with GDM to determine if early term induction would prevent one event of stillbirth, as we will discuss further on.

Evidence from observational studies

Given that there is only one randomized, controlled trial on this topic, it is important to look at observational studies on this topic. In observational studies, there is no “assignment” to an induction or expectant management—instead, researchers usually look back in time at what happened when women and their care providers decided to induce or use a policy of expectant management.

We searched PubMed for non-randomized studies that compared early induction for gestational diabetes at or near term versus expectant management. We restricted the search to studies published since 2010, since earlier studies usually included people with pre-existing Type 2 diabetes in addition to those with GDM (Witkop et al. 2009).

Four studies looked specifically at birth outcomes after early induction for gestational diabetes versus expectant management. Table 1 provides details about these four observational studies. We will also summarize their results below, starting with what the studies found about outcomes for mothers, and then what they found for babies.