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Preconception Diabetes Linked to Higher Preterm Birth Risk, Study Finds

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Among women in the US of reproductive age (18–44 years old), diabetes has a prevalence rate of 4.5%. Unfortunately, half of these cases are poorly controlled. It’s estimated that 1%–2% of women enter pregnancy with diabetes, while around 20% of women in this age range have prediabetes. Prediabetes is a metabolic state where blood glucose levels are higher than normal, but not high enough to qualify for a diabetes diagnosis.

Unfortunately, there is not enough documentation to determine the proportion of women entering pregnancy with prediabetes. Having diabetes before pregnancy is associated with negative pregnancy outcomes. Preconception diabetes can increase the odds of preterm birth by 3.5 times, according to a 2017 meta-analysis of 55 studies. On the other hand, there are only a few studies that have looked at the risks associated with preconception prediabetes. Of the few available, two studies found that glucose levels in the prediabetes range were linked with slightly higher birth weight but not with gestation length, while another study found that glucose levels in this range were associated with a small increased risk of preterm birth.

A new study examined the associations between preconception diabetes, prediabetes, and haemoglobin A1c (HbA1c) levels on the risk of preterm birth. The study, which also evaluated whether these associations were modified by access to or utilisation of healthcare services, is published in the peer-reviewed Journal of Women’s Health.

Preconception diabetes is strongly associated with adverse birth outcomes. In the current study, Erin Delker, PhD, from the University of California, San Diego and San Diego State University, and coauthors, found that both preconception diabetes and prediabetes were associated with increased risk of preterm birth. The investigators reported that the associations between preconception elevated HbA1c and preterm birth were greater among women without stable healthcare coverage. 

“Our findings, in aggregate with the existing literature, suggest that screening for hyperglycemia prior to pregnancy is important to identifying women who may experience greater risks of adverse birth outcomes,” explained the investigators.

In an accompanying editorial, Amber Healy, DO, from Ohio University Heritage College of Osteopathic Medicine, states that “Recommendations for the diagnosis and treatment of prediabetes in pregnancy are lacking.” Dr Healy concludes that “Better screening for prediabetes and diabetes preconception and increased access to contraception will prove beneficial in reducing preterm delivery. Engaging both primary care providers and obstetrics/gynaecology specialists in these strategies is key to these strategies succeeding.”

Although the study found that elevated blood glucose levels in women before pregnancy may increase the risk of preterm birth, there are some limitations to the study that need to be considered. One limitation is that self-reported preterm births were not differentiated between spontaneous versus indicated preterm births. Additionally, the prevalence of preterm birth in the sample was higher than anticipated, which suggests the possibility of misreporting of the outcome. However, the misclassification is unlikely to differ by diabetes status.

The study classified women who reported being told by a doctor that they had “high blood sugar or diabetes” as having diabetes. This classification could result in misclassification if women with prediabetes also responded positively to this question. The study also did not differentiate between Type I and Type II diabetes, measured glucose and HbA1c only once, and did not consider other pregnancy complications such as preeclampsia and gestational hypertension that could explain the increased risk of preterm birth associated with hyperglycemia.

The study sample included women who had a pregnancy between Waves IV and Wave V, which comprised women who were more educated and older during pregnancy, and a higher proportion was White compared to the baseline cohort. Due to small sample sizes, the study did not use Add Health sampling weights, although unweighted estimates in the analytic sample were similar to those previously published.

Despite these limitations, the research is strengthened by the measurement of glycemia before pregnancy. The study examined the risk of adverse birth outcomes across the full range of HbA1c and found an increased risk of preterm birth associated with blood glucose levels below clinical cutoffs for diabetes. The study also highlights the disproportionate burden of elevated preconception glucose levels among women with limited access to and utilisation of healthcare. Further monitoring could identify at-risk women earlier, provide opportunities for preconception intervention, and offer substantial benefits to population health.

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