Impact of late pregnancy haemoglobin A_1c at 29–30 weeks’ gestation on adverse pregnancy outcomes among women with pre-existing diabetes: a retrospective analysis

Abstract

This study was to assess the relationship between late pregnancy haemoglobin A_1C (HbA_1C) at 29–30 weeks of gestation and adverse pregnancy outcomes (APOs) in 272 pregnant women with pre-existing diabetes. HbA_1C ≥6.1% was associated with significantly increased risk of preterm delivery, Caesarean section, large for gestational age (LGA), neonatal respiratory distress, neonatal hypoglycaemia, and composite adverse neonatal outcome (p < .05). The risk of pre-eclampsia increased significantly at the lower HbA_1C cut-off of > 5.6% (p = .039). Reduction of HbA_1C cut-off from 6.1% to 5.6% improved the sensitivity but reduced the specificity for prediction of APOs. Overall, the receiver operating characteristic (ROC) curves demonstrated the moderate predictive value of late pregnancy HbA_1C for APOs. In conclusion, elevated late pregnancy HbA_1C levels at 29–30 gestational weeks had a negative impact on APOs in pregnant women with pre-existing diabetes. However, HbA_1C cut-off levels of neither ≥6.1% nor >5.6% were ideal for predicting APOs.

Impact statement

• What is already known on this subject: Poorly controlled diabetes is associated with adverse pregnancy outcomes (APOs). Periconceptual haemoglobin A_1C (HbA_1C) correlates well with the risk of foetal anomaly but is not predictive of APOs at time of delivery. New evidence suggested that late pregnancy HbA_1C is predictive of APOs but the definitions of a late pregnancy gestational week and target HbA_1C cutpoint remain in doubt.

• What the results of this study add: This study investigated the relationship between late pregnancy HbA_1C levels at 29–30 weeks of gestation and the APOs among pregnant women with pre-existing diabetes. Late pregnancy HbA_1C ≥ 6.1% correlated with the risk of APOs but the increased risk of pre-eclampsia only became significant at the lower cut-off of >5.6%. Reducing HbA_1C cut-off from 6.1% to 5.6% improved the sensitivity but reduced the specificity for prediction of APOs. Overall, late pregnancy HbA_1C had a moderate predictive value for APOs.

• What the implications are of these findings for clinical practice and/or further research: HbA_1C cut-off levels of neither ≥6.1% nor >5.6% were ideal in predicting APOs among pregnant women with pre-existing diabetes. As HbA_1C levels tend to drop in pregnancy, caution should be taken when interpreting HbA_1C in pregnancy. More multi-centred studies are required to explore the respective glycaemic target for each APO and to determine the ideal timing for late pregnancy HbA_1C measurement.

Keywords:

• Late pregnancy
• HbA_1C
• adverse pregnancy outcome
• diabetes
• glycaemic control

Acknowledgements

The authors wished to thank Mr Chuah Jun Sen for the assistance with data collection.

Disclosure statement

The authors declare no conflict of interest. The authors alone are responsible for the content and writing of the paper.