The Association Between Hba1c with Macrosomia/Large for Gestational Age in GDM; and Preterm Birth in Women with Diabetes Mellitus

A large number of pregnancies are complicated with diabetes, with number increasing in recent years. A mother can have diabetes prior to pregnancy [type1 or type 2 diabetes mellitus (DM)) or diabetes can appear for the first time during the pregnancy i.e., gestational diabetes mellitus (GDM). Irrespective of the type of diabetes it is associated with numerous adverse outcomes during and after pregnancy, for both the mother and the baby. The delivery of a big baby (macrosomia) is one of the main complications for women with GDM. The risk of macrosomia in women with GDM who have a high HbA1c remains unclear. In addition, preterm delivery is also very common amongst women with diabetes in pregnancy. The association between preterm birth and diabetes in pregnancy is yet to be fully established. Therefore, I aimed to perform two systematic reviews to identify the current knowledge about macrosomia and preterm birth in pregnancies complicated with diabetes.

Two systematic reviews were performed according to PRISMA and MOOSE guidelines. Different electronic database (Medline, Embase, The Cochrane library, CINAHL and Scopus) search was performed systematically to identify relevant articles of interest. All the citations were managed using ENDNOTE software. Data collection was performed using a standardised data extraction form. Data analysis was performed using STATA software.

The first systematic review in the thesis identified a significant association between high HbA1c and fetal macrosomia among GDM pregnancies. It indicated that women who have high HbA1c are at increased risk of delivering a macrosomic or large for gestational age (LGA) baby. Meta-analysis showed an increased risk ratio (RR) associated with high HbA1c of 1.75 (95% CI 1.30-2.35) for LGA, and 1.68 (CI 1.29-2.19) for macrosomia. Therefore, strict glycaemic control during pregnancy is essential. Mothers with GDM can be treated with medications and should be advised to maintain a healthy weight gain during the pregnancy.

The second systematic review identified a higher risk of preterm delivery among diabetic pregnancies compared with normal pregnancies. Moreover, the risk of preterm delivery is highest amongst type 1 DM women compared to type 2 DM and GDM. The overall RR for pregnancies complicated for any form of diabetes was estimated as 2.39 (CI: 2.02-2.82); for type 1 DM it was 4.01 (CI: 3.41-4.69), type 2 DM it was 2.63 (CI 2.19-3.16) and for GDM it was 1.29 (CI 1.20-1.37). Those mothers who were already classed as having diabetes prior to their pregnancy should aim to maintain strict glycaemic control before pregnancy. However, once pregnancy is confirmed they should receive regular blood glucose checks and maintain a healthy weight gain (for normal BMI women it is 11.5 -16.0 kg, overweight women 7.0-11.5 kg and obese women 5.0-9.0 kg).

It is vital to achieve good glycaemic control (between 4-7 mmol/L) to prevent all adverse outcomes in women with DM in pregnancy. Delivery of a healthy full-term baby is our main goal. It can breach the viscous cycle of DM, and thus reduce the burden of diabetes globally.