Gestational Diabetes

Published on: November 11, 2021

This month, midwife Emma McNerlin explores the implications of a diagnosis of gestational diabetes in pregnancy for both mother and baby.

By Emma McNerlin

What is Gestational Diabetes Mellitus (GDM)?

Gestational Diabetes Mellitus (GDM) is diabetes that first manifests or is diagnosed from the second trimester of pregnancy onwards. GDM pregnancy is categorized as high risk, requiring close monitoring for both mother and baby. A majority of cases of GDM are temporary and resolve after pregnancy. Approximately half of women diagnosed with GDM develop type 2 diabetes within ten years (International Diabetes Federation, 2020).

What causes GDM?

Pregnancy is normally a mildly diabetic state. Hormones produced by the placenta alter the mother’s metabolism to make glucose more readily available for her growing baby. However, for 7–10% of women worldwide, this natural change in pregnancy develops into GDM (Frontiers in Endocrinology, 2020). While the cause of GDM is unknown, some risk factors exist (see Table 1).


How is GDM diagnosed?

Since nearly all women with GDM are asymptomatic, screening is necessary to detect it. In Bangkok, this is usually conducted between weeks 24 and 28 of pregnancy. Some hospitals will also test earlier for those with the risk factors listed in Table 1.  A fasting blood plasma glucose level above 5.1 mmol/liter, or a two-hour plasma glucose level of 7.8 or above, indicates GDM (Diabetes Care, 2010). However, in Bangkok, some hospitals may use slightly varying levels for diagnosis. 

It should be noted that diabetes detected in the first trimester is not GDM but undiagnosed type 1 or type 2 diabetes. These conditions will not resolve post pregnancy and will require consultation and care with an endocrinologist (Diabetes UK, 2021). 

What are the complications of GDM for the expectant mother?

Pregnancies complicated by GDM require close monitoring and a comprehensive care team comprising an OB/GYN, endocrinologist, and dietitian, alongside self-testing and self-monitoring of glucose levels. This can cause anxiety and stress in the pregnancy, so a good support network is essential. There are lots of GDM resources online for women to connect and discuss their condition. The clinical complications of GDM for the mother include increased risk of developing high blood pressure, preeclampsia, and postpartum depression (Azami et al 2019). 

What are the complications of GDM for the baby?

GDM can also cause complications for the baby. Poorly controlled maternal blood sugars lead to increased delivery of nutrients to the baby, which stimulates them to produce more insulin. This fetal insulin acts as a growth factor, which can cause macrosomia (large baby). Conversely, in other cases of GDM, high blood pressure in the mother leads to fetal growth restriction and smaller than average babies. GDM also increases the risk of polyhydramnios (high levels of amniotic fluid), which can present further risks for preterm labour and birth. 

Babies born to GDM mothers more often require NICU treatment for a short time after birth, for respiratory complications as their lungs are under-developed for their age. These babies are also likely to require support for low blood sugar directly after birth as they are no longer receiving glucose through the cord. Sadly, pregnancies complicated by GDM are five times more likely to result in stillbirth than the general pregnant population (Tommy’s 2021). This is thought to be due to placental damage and poor circulation resulting from high blood sugars (Robson and Waugh 2013), and is why careful fetal monitoring and attention to fetal movements are especially important.  Recent research from the UK shows that diagnosing GDM and comprehensive management reduces the risk of stillbirth to almost that of the general population (Stacey et al 2019). 

How is GDM treated?

Around 80% of women will adequately control their blood sugars with diet and lifestyle changes and home blood glucose monitoring (NICE, 2021). Consultation with a dietitian is essential to ensure a balanced diet is followed. Those who are overweight or obese should be supported to limit their weight gain, to better control their GDM (Myles, 2020). Where there is poor diabetic control, or dietary and lifestyle measures are insufficient to decrease blood glucose levels, medications such as metformin are safe and can help. In the most serious cases, insulin is prescribed.

What are the implications of GDM for pregnancy, birth, and postpartum?


Most cases of GDM are diagnosed around 28 weeks at routine screening. It can take a few weeks to get used to the dietary changes and self-screening of blood sugars, so mothers shouldn’t get disheartened if it takes a while to bring them under control. 

Extra scans are required to monitor baby’s growth to ensure they are not becoming too big or growing too slowly; a macrosomic baby weighs over 4.5 kg at term, and a growth-restricted baby is one below 2.5 kg at term (NICE, 2021). In all cases, steroid injections may be administered to the mother around 34–36 to help mature the fetal lungs and mitigate the increased risk of preterm labour and breathing problems for baby after birth. Scans will also check for unusual increases in amniotic fluid levels. 

Women with GDM are also encouraged to harvest and freeze colostrum from the 37th week of pregnancy. This can be given to baby in the first hours after birth to help avoid hypoglycemia (low blood sugar). It is crucial to only start collecting colostrum from 37 weeks, as nipple stimulation can trigger labour (Gestational Diabetes UK, 2015).

There may be more frequent doctor visits in the last 8 weeks of pregnancy as high blood pressure is a common side effect of GDM, potentially requiring medication to control it.


Knowing the options for birth with GDM and the condition’s impact on the birth plan is important. Your OB/GYN should discuss these implications with you. Depending on the individual situation, induction of labour or a C-section planned at around 38 weeks may be advised. The medical team may also closely monitor maternal blood sugars in labour. For those choosing to labour and birth vaginally, continuous fetal monitoring is required due to increased risk of fetal distress. If wireless monitoring is available, then mobilizing is possible, making it easier to cope with labour, and ensuring baby rotates into a good position for birth.  Babies born to GDM mums gain mass around their trunk and shoulders in utero, so might experience shoulder dystocia, a complication where the baby’s head is born but the shoulders get impacted in the pelvis. When this happens, it is a birth emergency, which OBs are highly skilled to deal with. However, the risks and benefits of both C-section and vaginal birth should be explained to help the mother choose the right birth for her.


Maternal blood sugars usually resolve spontaneously after delivery as the hormones responsible for the GDM are no longer secreted . The medical team may monitor pre-meal levels for 24 hours after birth to ensure this is the case. If levels remain high, a referral to a specialist will be necessary. Immediately after birth, baby may be monitored in the NICU for signs of hypoglycemia, respiratory distress, and jaundice. Women who have had GDM are encouraged to breastfeed for at least two months and beyond to reduce their risk of developing type 2 diabetes later (Gunderson et al, 2015). GDM mothers should have another glucose tolerance test at six weeks postpartum. Before conceiving again, another test to rule out both type 1 and type 2 diabetes is advised.

Despite the increased risk of GDM pregnancy, it is important to remember that prenatal surveillance and highly developed protocols mean that most GDM mums have a straightforward pregnancy, and their babies thrive and develop normally through infancy and childhood. GDM is something to take seriously, but with compliance to dietary changes and close care and attention from the medical team, outcomes are good for both mother and baby.

 **The contents of this article are intended for informational use only and should not be considered as medical advice. If you are concerned about any aspect of your pregnancy, please consult your OB/GYN. ****

Photos from Canva.


Azami et al. (2019) The association between gestational diabetes and postpartum depression: A systematic review and meta-analysis. Diabetes Research and Clinical Practice, 149, 147–155.

Diabetes UK (2021) What Is Gestational Diabetes?

Frontiers in endocrinology (2020) Incidence and Risk Factors of Gestational Diabetes Mellitus: A Prospective Cohort Study in Qingdao, China.

Gestational Diabetes UK (2015) Colostrum Harvesting.

Gunderson et al (2015) Lactation and Progression to Type 2 Diabetes Mellitus After Gestational Diabetes Mellitus: A Prospective Cohort Study. Annals of Internal Medicine, 163(12), 889–98.

International Association of Diabetes and Pregnancy Study Groups Consensus Panel, Metzger BE, Gabbe SG, Persson B, Buchanan TA, Catalano PA, Damm P, et al. (2010) International association of diabetes and pregnancy study groups recommendations on the diagnosis and classification of hyperglycemia in pregnancy. Diabetes Care, 33(3), 676–682.

International Diabetes Federation (2020) Gestational Diabetes.

Myles, M. (2020) Midwifery Textbook for Midwives 17th Edition

NICE National Institute for Health and Care Excellence (2021) 

RCOG Advice on Diabetes in Pregnancy (2011) Diagnosis and Treatment of Gestational Diabetes.

Robson, S. and Waugh, J.(2013)  Medical Disorders in Pregnancy, 2nd Edition. Wiley-Blackwell.

Stacey et Al (2019) Gestational diabetes and the risk of late stillbirth: a case–control study from England, UK. BJOG, 126(8), 973-982.

Tommy’s (2021) Diabetes, fetal growth and stillbirth.

About the Author

Emma McNerlin is a UK trained and registered Midwife, First Aid Instructor and owner of Bumpsy Daisy Café and Community; a cafe and parenting community centre for new and expecting parents offering birthing classes, hypnobirthing, First Aid workshops and baby classes.

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