What does glucose tolerance before pregnancy say about PTB risk?


A large population-based cohort study in the American Journal of Obstetrics & Gynecology concluded that maternal prepregnancy impaired fasting glucose increases risk of preterm birth.

Preterm Birht

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A large population-based cohort study in the American Journal of Obstetrics & Gynecology (AJOG) has concluded that maternal prepregnancy impaired fasting glucose (IFG) increases risk of preterm birth (PTB), as well as either large or severe large for gestational age birth.

“It is now well accepted that reducing blood glucose in pregnancy reduces pregnancy and postpartum complications,” said principal investigator James Tang, PhD, an associate professor of maternal and child health at Guangzhou Medical University in Guangdong Province, China. “However, very few studies have investigated the impact of prepregnancy hyperglycemia on adverse pregnancy outcomes.”

Previous studies have suggested there are effective interventions for IFG, which reduce the mortality and delay the onset of diabetes.

“From the perspective of health management and disease prevention, identifying the association of IFG to adverse pregnancy outcomes is of substantial public health importance because it might be relatively easy to implement health interventions, plus helpful in decreasing the risk of adverse pregnancy outcomes in mothers who have IFG before pregnancy,” Dr. Tang told Contemporary OB/GYN

The cohort study consisted of 640,469 Chinese women from the National Free Preconception Health Examination Project (NFPHEP) who delivered singleton births in Guangdong Province from January 2013 to December 2017. Of the total participants, 4.84% met the World Health Organization (WHO)’s cut-point for IFG (fasting glucose concentration ≥ 6.1 mmol/L or greater and < 7.0 mmol/L), 5.10% had PTB, 1.12% had early PTB, 7.11% had large for gestational age (LGA) birth and 2.53% had severe large for gestational age (SLGA) birth. (SLGA was defined as birth weight by gestational age > 97th percentile.) 

Compared to women who were normoglycemic (fasting glucose concentration < 6.1 mmol/L), women with prepregnancy IFG had a 7.0% higher risk of PTB (adjusted risk ratio [ARR] 1.07; 95% confidence interval [CI]: 1.02 to 1.12), a 10.0% higher risk of LGA (ARR 1.10; 95% CI: 1.06 to 1.14) and a 17.0% higher risk of SLGA (AAR 1.17; 95% CI: 1.10 to 1.26).

Dr. Tang said although IFG is linked to an increased risk of PTB SGA birth, there is no linear association of fasting glucose concentration with PTB, indicating potentially different mechanisms of action. In addition, despite the WHO’s cut-point of IFG being inappropriate to identify PTB and LGA birth, “it is difficult to find a suitable cut-point for prepregnancy blood glucose to predict women who are at risk for these two conditions,” Dr. Tang said.

Screening for IFG before pregnancy and incorporating interventions to control fasting glucose before pregnancy, such as diet, weight control, physical exercise and counseling, “might be necessary to reduce the risk of preterm birth, large for gestational age birth and severe large for gestational age birth,” Dr. Tang said.

A separate, recent study from the Journal of Third Military Medical University (2019; 41(6): 594-599), which included women with prepregnancy IFG, found that lifestyle intervention could reduce the incidence of gestational diabetes and many adverse pregnancy outcomes like preterm birth.

Dr. Tang also noted that the WHO’s cut-point for IFG is restrictive and that healthcare providers should carry out continuous management of blood glucose, both before and during pregnancy.


Dr. Tang reports no relevant financial disclosures.

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