Don’t eat for two, mothers-to-be are told

Women who are overweight or obese during pregnancy are more likely to have large babies, a major study has found.

The study also found that mothers with high blood sugar or diabetes, even within a healthy range, also tend to have bigger babies.

Conversely, having higher blood pressure during pregnancy causes women to deliver smaller babies, researchers at the British universities of Bristol and Exeter, who led the study, found.

“Being born very large or very small can carry health risks for a newborn baby, particularly when that’s at the extreme end of the spectrum,” said Rachel Freathy of the University of Exeter Medical School, who co-wrote the report.

Understanding which characteristics of mothers influence birth weights may help reduce the number of babies born too large or too small, she added.

The study analysed data from 30,000 women and their babies over eight decades, and is the strongest evidence to date proving a link between the weight of mother and child. It found higher levels of the mother’s blood glucose during pregnancy caused babies to be larger — while higher blood pressure caused babies to be smaller.

The “normal” weight of a full-term baby is about 7lb 12oz. Smaller than 5lb 8oz is generally classed as low birth weight, larger than 8lb 13oz is high birth weight.

Healthy birth weight is important for the first year of life, and reflects how well the baby developed in the womb. Being born very large or very small can cause risks for child and mother, and is associated with type-2 diabetes later in the child’s life.

Dr Freathy confirmed mothers-to-be should not “eat for two” and said: “Our research supports the advice: attend antenatal appointments, eat healthily, exercise moderately in pregnancy.”

It has long been known that women who are overweight or have diabetes in pregnancy — gestational diabetes — tend to have bigger babies, but the new work is the first to measure genetic changes in the mother to look for cause and effect.

The seemingly contradictory finding on high blood pressure — which tends to go together with greater weight and higher blood sugar — shows the complicated factors in a baby’s development and the importance of monitoring during pregnancy, researchers said.

The study looked at women in Europe, the US and Australia from 1929 to 2013, and was published in JAMA, the journal of the American Medical Association.