Overweight and obesity during pregnancy causes a larger baby to be born. Even high blood sugar levels cause larger babies, while high blood pressure in the mother leads to smaller babies. This was shown in a new international study in which researchers at Sahlgrenska Academy collaborated.
It has long been known that overweight women and women with gestational diabetes tend to give birth to larger babies, but until now, it has been unclear if the baby’s size is caused by these maternal traits, and which factors are significantly involved in the connection between the size of the mother and the baby’s size.
International collaboration
In an international research collaboration led by the universities of Exeter and Bristol, in collaboration with researchers from Sahlgrenska Academy, researchers have been able to show that overweight and higher glucose levels during pregnancy lead to the baby being born with a higher birth weight, while high blood pressure in the mother causes a lower birth weight.
Larger babies
The group concluded that mothers with higher blood sugar levels tend to give birth to larger babies, even at levels that are not considered unhealthy.
“An extremely high or extremely low birth weight can be a health risk for the newborn infant. Higher and lower birth weights are also linked to diseases such as type 2 diabetes, later in life. Knowledge of which traits of the mother affect the baby’s birth weight can, in the future, help us to reduce the number of children that are born too large or too small,” says Dr. Rachel Freathy at the University of Exeter Medical School, one of the researchers that led the study.
More than 30 000 women
In contrast to what some other studies show, the new study published in the scientific journal, JAMA, shows that the mother’s blood lipids (fat levels) that are also related to overweight, are not felt to contribute to the infant’s birth weight.
Researchers used data from more than 30 000 healthy women and their children, in 18 different studies. They examined genetic variations that are linked to the mother’s BMI (body mass index), blood sugar and lipid levels, as well as blood pressure together with measurements of these traits, in connection with pregnancy. The also studied the weight of all children at birth. All of the women were of European ancestry and lived in Europe, the North America and Australia. Children born between 1929 and 2013 were included in the study.
Genetic method
"A large amount of previous research on pregnancy and birth weight has been based on observations, but that can make it difficult to determine what is the cause and what is the effect, which can create confusion for expectant mothers and for healthcare personnel. Our genetic method is more robust and provided clear evidence that a mother’s weight, blood sugar level and blood pressure affect the size of the baby,” says Dr. Jess Tyrrell at the University of Exeter Medical School, one of the researchers.
Complicated factors
“By collaborating with a large group of researchers, we were able to succeed in doing this extremely significant project. The next question to be highlighted is how the mother’s weight, blood sugar level and blood pressure, and their effects on the infant’s birth weight, affect the child later in life,” says Bo Jacobsson of Sahlgrenska Academy.
“Do children born to women with a high blood sugar level during pregnancy continue to be heavier throughout life?”
The study Genetic evidence for causal relationships between maternal obesity-related traits and birth weights was published in the March 15 issue of JAMA.
The Early Growth Genetics Consortium, that is behind the study, is an international research collaboration between researchers from the UK, Netherlands, Denmark, Norway, Finland Sweden, Germany, the USA, Australia and Canada.
Contact:
Bo Jacobsson, Professor at Sahlgrenska Academy
[email protected]
BY: Johanna Hillgren
A pregnant woman's weight, blood sugar levels and blood pressure affect the baby's size
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