Gestational diabetes

Gestational diabetes is defined as glucose intolerance first detected during pregnancy that is not clearly overt diabetes and disappears after delivery of the placenta following birth. This may include people that have pre-existing but undiagnosed diabetes before their pregnancy, but their true diagnosis is not identified until after delivery (National Institute for Health and Care Excellence (NICE), 2020).

Gestational diabetes does not present any overt symptoms unless blood glucose levels are very high. Even when symptoms do present, they are not unique to this condition and overlap with symptoms of pregnancy, for example:

• increased thirst
• tiredness
• increased urination
• genital infections (Hammoud et al, 2013)

As such, screening is an essential part of identifying people who are at risk.

During pregnancy, maternal tissues can become progressively resistant to insulin because of the influence of placental hormones and/or obesity on pregnancy. The hormonal changes increase physiological demands, with insulin requirements increasing by 200–250% to maintain a euglycemic state (Barbour et al, 2007). Gestational diabetes occurs when the pancreas cannot produce sufficient insulin to overcome insulin resistance and meet the increased demand. In people with obesity, this takes place because the pregnancy-induced insulin resistance occurs on top of pre-existing insulin resistance (Kampmann et al, 2015). As a result of the increased insulin resistance, maternal blood glucose levels rise and glucose is transported across the placenta to the fetus. This increases fetal blood glucose levels, which stimulates fetal insulin release. Insulin is a growth hormone, so the hyperinsulinaemia (high levels of insulin) stimulates fetal growth resulting in macrosomia (when a newborn has a birth weight over 4000 g) (Catalano et al, 2006;

In the UK, pregnant people are assessed for their risk during their antenatal appointments, and people identified as having at least one of the risk factors are offered testing for gestational diabetes.

The 75 g 2-hour oral glucose tolerance test (OGTT) is used at pregnancy weeks 24–28. If the patient has had gestational diabetes in a previous pregnancy, they should be offered early blood glucose monitoring and OGTT as soon as possible after booking in and at weeks 24–28 if found negative on the earlier test. People with a confirmed gestational diabetes diagnosis will be transferred from primary care and supported by a combined diabetes- and pregnancy-specialist healthcare team (NICE, 2020).

A diagnosis for gestational diabetes is made if the fasting plasma glucose level is 5.6 mmol/litre or above, or the OGTT result at 2 hours is 7.8 mmol/litre or above.

People with a diagnosis of gestational diabetes should be offered lifestyle guidance, blood glucose monitoring and, if requiring blood glucose-lowering medication, metformin or insulin (NICE, 2020).

Lifestyle guidance should include information about:

The advice should be given throughout the pregnancy, and is the foundation to treating gestational diabetes. However, if at diagnosis the blood glucose level is 7 mmol/litre or above, then insulin with or without metformin should be offered. If the blood glucose level is between 6 and 6.9 mmol/litre and there are complications (such as macrosomia or hydramnios), then the clinician should consider treating with insulin, with or without metformin.

If blood glucose levels are below 7 mmol/litre but a 1–2-week trial of lifestyle interventions does not meet the required blood glucose target, then the first-choice treatment of metformin should be initiated. If metformin

Barbour LA, McCurdy CE, Hernandez TL, Kirwan JP, Catalano PM, Friedman JE. Cellular mechanisms for insulin resistance in normal pregnancy and gestational diabetes. Diabetes Care. 2007;30 Suppl 2:S112-S119. https://doi.org/10.2337/dc07-s202

Berkowitz GS, Lapinski RH, Wein R, Lee D. Race/ethnicity and other risk factors for gestational diabetes. Am J Epidemiol. 1992;135(9):965-973. https://doi.org/10.1093/oxfordjournals.aje.a116408

Catalano PM, Ehrenberg HM. The short- and long-term implications of maternal obesity on the mother and her offspring. BJOG. 2006;113(10):1126-1133. https://doi.org/10.1111/j.1471-0528.2006.00989.x

Dashora U, Temple R, Murphy H, et al. Management of glycaemic control in pregnant women with diabetes on obstetric wards and delivery units. 2017. http://www.diabetologists-abcd.org.uk/JBDS/JBDS_Pregnancy_201017.pdf (accessed 27 June 2023)

Hammoud NM, de Valk HW, Biesma DH, Visser GH. Gestational diabetes mellitus diagnosed by screening or symptoms: does it matter?. J Matern Fetal Neonatal Med. 2013;26(1):103-105. https://doi.org/10.3109/14767058.2012.722718

Kampmann U, Madsen LR, Skajaa GO, Iversen DS, Moeller N, Ovesen P. Gestational diabetes: A clinical update. World J