FRIDAY, Nov. 4, 2016 (HealthDay News) -- Urine samples in pregnancy may help doctors assess fetal growth and individualize recommendations for the baby's health, a new study contends.

Abnormal fetal growth and birth weight are risk factors for chronic diseases later in life, including type 2 diabetes and obesity, the researchers noted.

But metabolic substances in a mother's urine appear to indicate how large a baby will be at birth, the researchers said.

Doctors ccould then suggest lifestyle changes to help maintain healthy fetal size, the researchers said in the Nov. 3 issue of BMC Medicine.

"We used a technique called NMR spectroscopy to identify, for the first time, a panel of 10 urinary metabolites in the third trimester of pregnancy that were associated with greater fetal growth and increased birth weight," said study co-lead author Mireille Toledano, of Imperial College London in England.

"These metabolites included steroid hormones and important biological building blocks called branched-chain amino acids [BCAAs]," she said in a journal news release. These amino acids are nutrients that provide energy for the growing fetus.

Changes in these amino acids and other metabolites detected in a mother's urine explained 12 percent of the variation in birth weight. The finding was independent of other known factors such as a mother's weight and smoking or drinking, the researchers said.

For the study, urine samples and lifestyle information were collected from more than 800 pregnant women, ages 28 to 33, in Spain.

"We found that a 50 percent increase in the mother's level of individual BCAAs equated to a 1 to 2.4 percent increase in birth weight," said study co-lead author Muireann Coen, also of Imperial College London. This was the equivalent of 5 to 11 grams (less than an ounce), she said.

"When we made comparisons with the lifestyle and environmental exposures of the women in our study we found that the variability between BCAA profiles of individual mothers could be partially explained by levels of physical activity, vitamin D, coffee consumption and smoking exposure, suggesting them to be potential areas of intervention to promote a healthy birth weight," Coen said.

The study only found an association between levels of branched-chain amino acids and abnormal growth patterns, not a direct cause-and-effect relationship.

Still, "this proof-of principle study highlights the value metabolic profiling of pregnant women could have on personalizing pregnancy plans to improve fetal growth outcomes," the researchers said.

More information

The American Academy of Family Physicians offers tips for a health pregnancy.