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Gestational diabetes risk may be higher during hot summer months

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Pregnant women may be more likely to develop gestational diabetes during the hotter summer months, suggests a new study.

More than 11,500 pregnant women took part in the three-year study by Swedish researchers, which set out to look at seasonal variations in glucose tolerance and the diagnosis of gestational diabetes.

All study participants took a standard two-hour glucose tolerance test in the 28th week of pregnancy.

Over the study period, 487 women – or 4.2% – were diagnosed with gestational diabetes, with diagnosis rates increasing during the summer months and peaking in June.

The researchers also looked at temperature data and found glucose levels tended to increase when it was hotter.

Overall, the summer months of June, July and August were linked to a 51% increase in gestational diabetes.

The researchers presented their findings this week at the European Association for the Study of Diabetes’s annual meeting in Munich (see attached PDF below).

Meanwhile, a separate study by researchers from the UK and Ireland highlighted the strong link between increased blood glucose levels during pregnancy and the risk of complications around the time of birth.

However, they said it was unclear exactly when health professionals should intervene to bring blood glucose levels down, with no obvious threshold for diagnosing gestational diabetes.

Their research, published in the British Medical Journal, combined and analysed data from 23 studies from around the globe involving more than 200,000 women and their babies.

As glucose levels increased, there was an equivalent increase in women needing to have a caesarean section or labour induced, while babies were more likely to be heavy and get stuck during birth.

This “straight line pattern” meant when doctors and nurses were trying to weigh up the risks and benefits of treating high blood sugar, there was no obvious point to start treatment, said researchers.

They said there was an urgent need to work out the optimum threshold for intervention.

“What we now need to work out is what the best threshold is for balancing the benefit of preventing pregnancy and birth problems – by detecting and treating women with high blood glucose levels against the costs of detection and treatment and the problems of over-treating some women and causing problems,” they added.

  • Table providing the number of oral glucose tolerance tests (OGTTs) performed and the percentage of women diagnosed with OGTTs for month and season:
 Month/SeasonOGTTnGDMn (%)

January

February

March

April

May

June

July

August

September

October

November

December

1094

928

1082

1027

1057

1009

974

928

781

835

897

926

36 (3.3)

34 (3.7)

31 (2.9)

34 (3.3)

41 (3.9)

59 (5.8)

50 (5.1)

52 (5.6)

33 (4.2)

42 (5.0)

38 (4.2)

37 (4.0)

Winter

Spring

Summer

Autumn

2948

3166

2911

2513

 107 (3.6)

106 (3.3)

161 (5.5)

113 (4.5)

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