The value of Flash Glucose Monitoring in diagnosing gestational diabetes mellitus in pregnant women after bariatric surgery.

Obesity is a global and fast growing health problem. The number of obese women
has increased 5-fold since 1975. One of the treatments for obesity is bariatric
surgery. The desire to have children is among the top 5 reasons for Dutch women
to request this type of treatment. Indeed, the chance of pregnancy is increased
58% after bariatric surgery.

The outcomes of pregnancy are greatly improved after bariatric surgery. There
are nonetheless maternal and fetal risks, such as alimentary deficiencies,
dumping syndrome, and an increased risk of the child being small for
gestational age (SGA). The risk of gestational diabetes mellitus (GDM) is
smaller for women after bariatric surgery If compared to obese women who did
not undergo this procedure, but is still higher if compared to the normal
population. It therefore remains important to perform screening for GDM in
women who became pregnant after bariatric surgery.

The gold standard for diagnosing gestation diabetes is the oral glucose
tolerance test (OGTT). However, this test is contraindicated in women after
bariatric surgery due to the high risk of symptomatic hypoglycaemia. Instead a
4-points self-monitoring blood glucose (SMBG) profile is acquired on a single
day, comprising a fasting glucose and glucose measurements 1 hour after the
meal. The SMBG profile is abnormal if one of the values exceeds a predefined
limit (5.3 mmol/l for fasting glucose, 7.8 mmol/l for postprandial glucose).
The reliability of this method for diagnosing GDM is unknown.

Recently the FreeStyle Libre (FSL) has become widely available as a relatively
inexpensive method to continuously measure interstitial glucose levels. It is
able to produce reliable 24-hour glucose patterns and trends.

The current study will investigate whether the FSL can be used to establish the
diagnosis GDM in women who became pregnant after bariatric surgery. To
accomplish this, first it will be necessary to gain insight into the continuous
glucose pattern of women, with and without gestational diabetes, who are
pregnant but did not undergo bariatric surgery.

This study is a cross-sectional pilot study and will take place in the
Elisabeth TweeSteden hospital in Tilburg, the Netherlands. The study contains 4
research groups that each will include 10 subjects:
1) pregnant women without GDM, i.e. normal OGTT;
2) pregnant women with GDM i.e. abnormal OGTT;
3) pregnant women with a history of bariatric surgery;
4) fertile non-pregnant women with a history of bariatric surgery.
In groups 1 to 3, the OGTT or 4-points SMBG will take place according to
protocol in the 25th week of pregnancy. Directly after this test is performed,
a research period of 7 days will start in which the FSL will be worn by the
subject to generate a continuous glucose pattern. Data will be collected in
Libreview. Directly afterwards, if warranted, treatment for GDM will start
according to hospital guidelines. For group 4, a similar research period of 7
days will take place after pregnancy and diabetes mellitus are excluded. These
women will also perform a 4-points SMBG on a single day during this 7 day
period.

Analysis
Diagnostic FSL-based criteria for GDM will be sought by comparing continuous
glucose patterns between women with and without GDM (group 1 and 2). These
criteria will be applied to pregnant women after bariatric surgery (group 3) to
establish an FSL-based diagnosis of GDM. The reliability of the devised
criteria will be assessed by analysing the glucose patterns of non-pregnant
women after bariatric surgery (group 4) and by comparing to the outcomes of the
4-points SMBG in both group 3 and 4.

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