COVID-19 May Have Worsened GDM Pregnancy Outcomes

Liam Davenport

April 27, 2021

Women diagnosed with gestational diabetes mellitus (GDM) during the COVID-19 pandemic were diagnosed later in their pregnancy than those diagnosed prior to the pandemic, suggests an audit of almost 1000 pregnancies at a leading UK hospital.

GDM-related births during the COVID era were significantly more likely to be large for gestational age, delivered via caesarean section, and associated with shoulder dystocia.

"This worrying research suggests that the coronavirus pandemic is having a negative effect on pregnancy care," commented Dr Lucy Chambers, head of research communications at Diabetes UK, in a news release.

"As the pandemic continues and we move towards an uncertain future, it's vital that measures are put in place to ensure that diabetes care during pregnancy continues to meet the highest standards."

The research was presented at the Diabetes UK Professional Conference 2021.

In other findings at the meeting, visceral fat thickness on ultrasound was found to be significantly increased in women who developed the condition, with a cut-off of around 4 cm increasing the risk of GDM sevenfold.

Ultrasound-measured visceral adipose tissue depth (VAD) is an "easily performed and effective tool for the prediction of gestational diabetes in at-risk pregnancies", said lead researcher Dr Robert D'Arcy, regional centre for endocrinology and diabetes, Royal Victoria Hospital, Belfast, and is "superior" to established risk factors.

Later Diagnosis

For the first study, Dr Jane Hirst, University of Oxford, studied 664 women who were diagnosed with GDM between August 2018 and April 2020, and 275 diagnosed between April 2020 and the end of January 2021.

All of the women were treated at Oxford University Hospitals NHS Foundation Trust, and delivery outcomes were available for 651 pre-COVID-19 and 193 COVID-era pregnancies.

Despite monthly fluctuations, the overall number of women that the team saw per month with GDM during the COVID-19 pandemic was not significantly different from the pre-COVID period.

"What we did find that was significantly different, however, was when women were diagnosed," Dr Hirst said, with a peak in diagnosis around 26 weeks prior to COVID. "Yet during COVID-19 this was closer to 28/29 weeks of gestation."

There was also a small peak in GDM cases after 35 weeks "and this corresponds in our Trust to when all-women have a third trimester growth scan at 36 weeks".

Ethnicity Differences

In terms of baseline characteristics, there were few differences between women in the pre- and during COVID-19 periods, "but there were some differences that were important to note".

These include ethnicity, with more women from Black ethnic groups detected as having GDM during COVID, at 8.9% versus 2.4% (p=0.02 for trend).

Importantly, the management of GDM remained "fairly constant" between the two periods, with around 45% managed through diet and exercise alone, and between 32% and 37% treated with metformin alone.

Increase in Adverse Outcomes

"What was significant," Dr Hirst continued, "was the difference in the size of these babies when they were born."

During the COVID period, the babies were heavier, at a mean birthweight of 3476g versus 3330g in the pre-COVID period.

There were consequently more babies who were large for gestational age during COVID than previously, at 35% versus 24%, or an odds ratio adjusted for baseline differences and birthweight of 1.8.

Caesarean section was also more common in the COVID era, performed in 46% of women versus 36% before the pandemic, or an adjusted odds ratio of 1.4.

"And, sadly, we also experienced more cases of shoulder dystocia in those women who were attempting vaginal birth," at 9% versus 2%, or an adjusted odds ratio of 2.6.

In contrast, there were no changes in gestational age at birth or prematurity, and no changes in rates of perinatal death or neonatal intensive care unit admission. 

Important Questions

The findings raise some important questions, Dr Hirst said, including whether they are unique to their institution and whether lockdown had an impact on dietary choices and exercise that could explain the differences.

Above all, "this data shows the need for a national diabetes audit for women with GDM so we can really benchmark our findings against other Trusts".

Anne Dornhorst, professor of practice, Centre for Endocrinology, Imperial College London, who chaired the session on GDM, said the delay in diagnosis seen in the study is "interesting because that's a delay in treatment at a very critical time," adding that the study is "phenomenally important work".

Poor GDM Prediction

In the second study, Dr D'Arcy explained that the National Institute for Health and Care Excellence (NICE) recommends in its diabetes in pregnancy guidelines the selection of women for GDM testing at 24–28 weeks gestation based on several risk factors.

These are a body mass index (BMI) above 30, previous macrosomia, a family history of diabetes, a high-risk ethnicity or previous GDM. However, the risk factors perform poorly as predictors of GDM, with a positive predictive value of just 20.8%.

He continued that body mass index (BMI) has a "complex relationship with metabolic risk," and is a "relatively weak predictor" of GDM development, at a positive predictive value of "only 20%".

Dr D'Arcy explained that this is because there is variability in the risk profile for any given value, due to the presence of "unhealthy lean" and "seemingly healthy obese" individuals.

This can be attributed to differences in visceral adiposity, which is linked to high intra-abdominal and ectopic fat deposition in liver and skeletal muscle, and subcutaneous adiposity, which is relatively low risk and associated with a protective effect in women with lower-body fat.

Ultrasound in Triplicate

To examine the performance of ultrasound measured maternal visceral adipose tissue depth (VAD) and subcutaneous tissue depth (SCD) as a tool for GDM prediction, the team conducted a nested observational study of women who took part in the SHAPE Study.

They recruited 151 women, all of whom had at least one risk factor for GDM, of whom 28 could not undertake an oral glucose tolerance test (OGTT) due to the COVID-19 pandemic.

At the antenatal booking, VAD and SCD was measured on ultrasound in triplicate and then averaged, blood was taken for HbA1c measurement, and serum and plasma samples were taken for storage.

OGTT was performed at 24–28 weeks, alongside another plasma and serum draw, and the patients then continued on routine care.

Significant VAD Differences

The average age of the women at the antenatal booking was 29.8 years, and the mean BMI was 30.

Dr D'Arcy noted that 74 of the 123 women who completed the study had a BMI ≥30, 53 had a family history of diabetes, eight had prior macrosomia and nine had a high-risk ethnicity.

The results showed that there was no significant difference in SCD between women with GDM and those without, at 2.13 cm versus 1.93 cm.

In contrast, the VAD was significantly greater in women diagnosed with GDM, at 4.22 cm versus 3.12 cm in those without GDM.

Double the Predictive Power

Further analysis revealed that a cut-off for VAD of ≥3.98 cm was a significant predictor of GDM, at an area under the receiver operating curve of 0.751, a sensitivity of 73.1% and a specificity of 72.2%.

Specifically, among women with a VAD ≥3.98 cm, 41.3% developed GDM, compared with 9.09% of those with a VAD <3.98 cm. This translated into an odds of GDM of 7.04 or a relative risk of 4.54.

"The positive predictive value of visceral adipose depth in this range was 41.3%, which is essentially twice that of BMI and twice that of the other NICE risk factors in general."

Dr D'Arcy said that further research nevertheless is required to "establish the role of VAD measurement in broader cohorts of pregnant women".

Encouraging Research

"Gestational diabetes increases the risk of serious complications during pregnancy, so it's encouraging to see research showing that a quick assessment using ultrasound can help to spot those most at risk early on in pregnancy," Faye Riley, senior research communications officer at Diabetes UK, commented in a news release.

"This assessment tool could in future be incorporated into routine care to help more women who are at risk of gestational diabetes get the support they need early on in their pregnancy."

No funding or conflicts of interest declared.

No relevant financial relationships declared.

Diabetes UK Professional Conference 2021: Abstract P67. Presented 19 April.

Diabetes UK Professional Conference 2021: Abstract P230. Presented 26 April.


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