Obesity in Pregnancy May Up Risk of Child With Type 1 Diabetes

Marlene Busko

April 29, 2015

Women who were obese in the first trimester of pregnancy were 33% more likely to have a child with type 1 diabetes than pregnant mothers with normal body weight, as long as neither parent had any type of diabetes previously, a new study has found.

But in this cohort of roughly 1.2 million children born in Sweden over a 14-year period, a child was still most likely to develop type 1 diabetes if either parent had type 1 diabetes, regardless of parental ethnicity, confirming that this is a highly heritable disease, say Dr Hozan I Hussen (Karolinska Institutet, Stockholm, Sweden) and colleagues in their paper published online April 27 in Diabetologia.

The novel finding that maternal obesity in nondiabetic mothers confers an increased risk of type 1 diabetes has "important public-health implications," senior author Dr Tahereh Moradi (Karolinska Institutet, Stockholm, Sweden) told Medscape Medical News.

The results suggest that strategies to reduce overweight and obesity before and during pregnancy could reduce the incidence of type 1 diabetes, which is currently increasing in children in most countries of the world.

"Preventing high body mass index [BMI] during pregnancy [may help] prevent the offspring from developing type 1 diabetes," Dr Moradi observed.

Asked to comment, Dr Nancy Butte (Baylor College of Medicine, Houston, Texas) said that "first and foremost, the study confirmed that heredity (paternal or maternal) for type 1 diabetes is the strongest risk factor for the development of type 1 diabetes in the offspring."

Second, "high maternal BMI was associated with increased risk of type 1 diabetes in offspring of parents without diabetes, [and] this study newly explores the combined effect of both risk factors," noted Dr Butte, who is a member of the US Obesity Society.

These findings provide another reason that young women should try to reach and maintain a normal BMI before they become pregnant and then strive to gain only an appropriate amount of weight during pregnancy, she added.

Maternal Obesity Plays a Role, but Heredity Most Important

Dr Hussen and colleagues explain that the incidence of type 1 diabetes in children is increasing in Sweden, as is the prevalence of maternal overweight/obesity. "Therefore, the aim of this study was to investigate if maternal overweight/obesity increases the risk of type 1 diabetes in offspring of parents with and without diabetes and of different ethnicities."

Although type 1 diabetes has been associated with parental diabetes and with a much higher risk conveyed from the father (6.6%) than from the mother (2.3%), the majority of children developing type 1 diabetes do not have parents with diabetes, they observe.

Previous studies have reported conflicting findings about whether or not high maternal BMI is a risk factor for type 1 diabetes in the offspring, but no study has tried to tease out how genetic factors and maternal obesity both contribute to this risk or whether these risk factors vary depending on parental country of birth, they note.

To investigate this, they analyzed registry data from 1,263,358 children who were born in Sweden between 1992 and 2004; they followed the children from birth until 2009. The mothers were grouped into 4 categories of BMI during the first trimester of pregnancy: < 18.5 (underweight), 18.5 to < 25 (normal weight), 25 to < 30 (overweight), and > 30 kg/m2 (obese).

A total of 5771 children were diagnosed with type 1 diabetes during the study period. Almost all children, 5155, had parents who were born in Nordic countries (mainly Sweden, but also Norway, Finland, Denmark, and Iceland); 322 children had parents who were born in non-Nordic countries (mainly Northern and Eastern Africa and other European countries), and 294 children had one Nordic and one non-Nordic parent.

On average, the children were diagnosed with type 1 diabetes when they were about 7.5 years old.

Among children with two Nordic parents, those whose mothers had type 1 diabetes had a significant 6.19-fold higher risk of having type 1 diabetes compared with children whose mothers did not have diabetes; those whose mothers had any type of diabetes (including type 2 diabetes and gestational) also had a significant 3.17-fold higher risk of having type 1 diabetes.

Furthermore, compared with children whose fathers had no diabetes, those whose fathers had type 1 diabetes had a significant 7.59-fold higher risk of having type 1 diabetes; those whose fathers had any type of diabetes had a significant 5.27-fold higher risk of having type 1 diabetes.

And women who were obese — but neither they nor the child's father were diabetic — had an increased risk of having a child with type 1 diabetes compared with pregnant women who had a normal BMI (incidence rate ratio [IRR], 1.33).

But this risk was not elevated for obese women if they or the child's father were diabetic — defined as type 1 diabetes or type 2 diabetes, or, in the mother, gestational diabetes (IRR, 0.96).

"The finding that first-trimester maternal obesity was a risk factor for type 1 diabetes only in offspring of parents without diabetes and with no further increment in risk in offspring of parents with diabetes clearly suggests that heredity for type 1 diabetes is the strongest risk factor of the two for development of type 1 diabetes in the next generation," say Dr Hussen and colleagues.

Nevertheless, increasing incidence of type 1 diabetes in children with nondiabetic parents may partly be explained by increasing prevalence of maternal overweight/obesity, they add.

The study therefore draws attention to the importance of "routine surveillance of gestational weight gain and postpartum weight retention, education on the importance of conceiving at a normal BMI…[and] development of interventions designed to assist women in meeting [gestational weight gain] guidelines," Dr Butte stressed.

The study was supported by the Swedish Research Council for Health, Working Life and Welfare (FORTE) and the Ministry of Higher Education and Scientific Research-Kurdistan Regional Government in Iraq. The authors have no relevant financial relationships.

Diabetologia. Published online April 27, 2015. Article

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