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Planning a pregnancy: how tight does blood sugar control need to be?

 

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    December 17th, 2016  Diabetes in Control

 

 

The results from a new study show that risk increased in women with an early HbA1c of at least 5.9% regardless of a gestational diabetes diagnosis later in pregnancy.

Risk of obstetric complications increases linearly with rising maternal glycemia. Testing HbA1c is an effective option to detect hyperglycemia, but its association with adverse pregnancy outcomes remains unclear. Emerging data sustains that an early HbA1c≥5.9% could act as a pregnancy risk marker.

The purpose of the study was to determine, in a multi-ethnic cohort, whether an early ≥5.9% HbA1c could be useful to identify women without diabetes mellitus at increased pregnancy risk. Primary outcome was macrosomia. Secondary outcomes were pre-eclampsia, preterm birth and Caesarean section rate.

1,228 pregnancies were included for outcome analysis. Women with HbA1c≥5.9% (n= 48) showed a higher rate of macrosomia (16.7% vs. 5.9%,p= 0.008) and a tendency towards a higher rate of preeclampsia (9.32% vs. 3.9% ,p= 0.092). There were no significant differences in other pregnancy outcomes. After adjusting for potential confounders, an HbA1c≥5.9% was independently associated with a three-fold increased risk of macrosomia (p= 0.028) and preeclampsia (p= 0.036).

They evaluated data on 1,228 pregnant women from April 2013 to September 2015 to determine whether an early HbA1c of at least 5.9% can identify women at increased risk for adverse pregnancy outcomes.

Participants were screened for gestational diabetes at 24 to 28 weeks’ gestation, and HbA1c measurement was added to first antenatal blood tests. The primary outcome of the study was macrosomia, and secondary outcomes included rates of preeclampsia, preterm birth and caesarean section.

Compared with participants with an HbA1c less than 5.9% (n = 48), participants with an HbA1c of at least 5.9% (n = 1,180) were more often members of ethnic minorities, had higher pre-pregnancy BMI, were more likely to have anemia and microcytosis, and were more likely to be diagnosed with gestational diabetes.

The rate of macrosomia was increased nearly threefold in participants with HbA1c of at least 5.9% compared with participants with HbA1c less than 5.9%; there also was an increased tendency toward preeclampsia. The rates of preterm birth and caesarean section did not differ significantly between the two groups.

Among participants with HbA1c of at least 5.9%, 22 were diagnosed and treated for gestational diabetes.

From the results of the study it was concluded that, in a multiethnic population, an early HbA1c ≥5.9% measurement identifies women at high risk for poorer pregnancy outcomes independently of GDM diagnosis later in pregnancy. Further studies are required to establish cutoff points adapted to each ethnic group and to assess whether early detection and treatment are of benefit.

In an earlier study published by the American Diabetes Association (Diabetes Care, 2014) they demonstrated that a simple A1c blood test can uncover hidden type 2 diabetes in expectant mothers. The study found that the A1c test can accurately detect undiagnosed type 2 and prediabetes in pregnant women.

The hemoglobin A1c done early in pregnancy may be a convenient and effective way to identify women with pre-existing type 2 diabetes or who are at greater risk of worse pregnancy outcomes.

In this study, researchers examined the use of an A1c measurement done during the first trimester as a screening tool for pre-existing diabetes. The test was performed on more than 16,000 pregnant women and compared with the results of a 2-hour oral glucose tolerance test (OGTT), which is performed after an overnight fast, and is the gold standard diagnostic test for type 2 diabetes.

The study found that the hemoglobin A1c test was able to identify all the women with pre-existing type 2 diabetes when an A1c cutoff point of 5.9 percent was used, said Dr. Florence Brown from Joslin Diabetes Center in Boston.  “In addition, even if women did not have pre-existing diabetes, the A1c cutoff point of 5.9 was able to identify a population of women at greater risk for adverse pregnancy outcomes, including some women with gestational diabetes.”

This is an important finding because 5.9 percent is considerably lower than the value of 6.5 percent currently used to diagnose patients with type 2 diabetes who are not pregnant, she adds. The 6.5 percent threshold would have missed almost half of these women and is therefore too high for screening purposes, the study authors conclude.

This study also found that an early pregnancy A1c of 5.9 percent to 6.4 percent was associated with a greater risk of worse pregnancy outcomes, including birth defects, preeclampsia and perinatal death.

Given that the prevalence of type 2 diabetes is increasing, the A1c test done as early as possible could identify women at high risk and improve pregnancy outcomes. “This study supports the use of an A1c test in the first trimester and ideally with the first prenatal visit as one possible screen for pregnant women,” said Dr. Brown.

Practice Pearls:

  • A1c test in the first trimester and ideally with the first prenatal visit is one possible screen for pregnant women.
  • An A1c test done as early as possible could identify women at high risk and improve pregnancy outcomes.
  • All pregnant women should undergo screening for diabetes and prediabetes at initial appointment and also later in their pregnancy.

Mañé L, et al. J Clin Endocrinol Metab. 2016;doi:10.1210/jc.2016-2581.

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