PHILADELPHIA – An elevated postpartum fasting blood sugar does not predict type 2 diabetes in women who had gestational diabetes.
Out of nine women with an elevated fasting glucose after giving birth, only two went on to a diagnosis of type 2 diabetes 6 weeks later, Dr. Hilary Roeder said at the annual scientific sessions of the American Diabetes Association.
"That means that if we had used the postpartum glucose value as a diagnostic tool, seven women would have been misdiagnosed," Dr. Roeder, an ob.gyn. at Scripps Health in San Diego, said in an interview. "We still have no good way to know specifically which women with gestational diabetes will subsequently develop type 2 diabetes."
For women with gestational diabetes, an oral glucose tolerance test should be done 6 weeks after delivery, the American Diabetes Association recommends. But some new mothers don’t make it back to the doctor at that time, Dr. Roeder said.
"We still have no good way to know specifically which women with gestational diabetes will subsequently develop type 2 diabetes."
"The problem with formal screening at the 6-week postpartum appointment is that patients don’t always come back for this visit," she said. "They get busy with the new baby or have already gone back to work and they don’t follow up. Or if they do, they often are not fasting – a requirement to perform formal screening for type 2 diabetes. Our thought was that if we could diagnose them prior to discharge from the hospital, we could set up a follow-up visit with a primary care physician or an endocrinologist so they can get proper care."
She employed a retrospective cohort study to determine whether postpartum glucose on the day of delivery was associated with a later type 2 diabetes diagnosis. Although there were 545 patients with gestational diabetes in the records, only 165 (30%) had a formal diabetes screen at 6 weeks – illustrating the poor rate of follow-up in the cohort.
Of those who were tested at 6 weeks, 111 also had a postpartum fasting glucose available for review. The patients had a mean age of 32 years, with a mean body mass index of 31 kg/m2. They had a mean gestation of 25 weeks when diagnosed with gestational diabetes.
Nine of those with a postpartum test had glucose levels above 126 mg/dL. But 6 weeks later, only two of those women were found to have type 2 diabetes.
When Dr. Roeder compared the postpartum glucose levels between patients, she found no significant difference between those who developed type 2 diabetes and those who did not. In fact, had the diagnosis been made immediately post partum, six additional women who did develop diabetes would have been missed, as their blood sugar was less than 126 mg/dL after delivery.
Overall, postpartum blood glucose levels were significantly higher than 6-week levels (mean 101 mg/dL vs. 93 mg/dL). Dr. Roeder said she believes human placental lactogen and other placentally-derived hormones could be responsible for this in part. The hormones keep glucose in the maternal bloodstream, making it more available for fetal metabolism. This results in higher maternal glucose levels, which take some time after birth to decline.
"Even though the placenta has been removed, the hormones are still circulating for an indefinite time after birth," she said.
Because immediate postpartum testing does not appear helpful, Dr. Roeder said it’s critical that women with gestational diabetes attend their 6-week checkup and have a full diabetes screen.
"We really need to impress upon our patients how important this visit is to their future health."
Dr. Roeder had no financial disclosures.