While it’s not necessary to "eat for two" while pregnant, women are encouraged to gain about 25 to 35 pounds during those 40 weeks, depending on her pre-pregnant weight.

Focus on weight gain during pregnancy tends to be on the "too much" side -- women who gain more than 35 pounds can possibly do harm to both their health and the health of the growing fetus -- but a new study focuses on what happens when a women gains too little weight.

Researchers from The University of Texas Health Science Center San Antonio reported Monday that eating less during early pregnancy impaired fetal brain development in a nonhuman primate model.

While primates were used for the study, the researchers said primate model's brain developmental stages are very close to those of human fetuses.

The researchers found decreased formation of cell-to-cell connections, cell division and amounts of growth factors in the fetuses of mothers fed a reduced diet during the first half of pregnancy.

"This is a critical time window when many of the neurons as well as the supporting cells in the brain are born," said Peter Nathanielsz, M.D., Ph.D., director of the Center for Pregnancy and Newborn Research in the Health Science Center School of Medicine.

The study included collaborators at the Southwest Foundation for Biomedical Research (SFBR) in San Antonio and Friedrich Schiller University in Jena, Germany.

Baboon mothers

The team compared two groups of baboon mothers located at SFBR's Southwest National Primate Research Center. One group ate as much as they wanted during the first half of pregnancy while the other group was fed 30 percent less, a level of nutrition similar to what many prospective mothers in the U.S. experience.

SFBR's Laura Cox, Ph.D., said their collaboration allowed them to determine that the nutritional environment impacts the fetal brain at both the cellular and molecular levels.

"That is, we found dysregulation of hundreds of genes, many of which are known to be key regulators in cell growth and development, indicating that nutrition plays a major role during fetal development by regulating the basic cellular machinery," said Cox.

Marked nutrient restriction, such as in famine conditions, is known to adversely affect fetal brain development.

Senior author Thomas McDonald, Ph.D., also of the Health Science Center, said the study "is the first demonstration of major effects caused by the levels of food insecurity that occur in sections of U.S. society and demonstrates the vulnerability of the fetus to moderate reduction in nutrients."

Poverty can be a cause of food insecurity, but the study also raises other ways fetuses may not get the nutrition they need.  

Nathanielsz noted in teenage pregnancy, the developing fetus is deprived of nutrients by the needs of the growing mother; in pregnancies late in reproductive life, a woman's arteries are stiffer and the blood supply to the uterus decreases, inevitably affecting nutrient delivery to the fetus; and diseases such as preeclampsia or high blood pressure in pregnancy can lead to decreased function of the placenta with decreased delivery of nutrients to the fetus.

Maternal health

"This study is a further demonstration of the importance of good maternal health and diet," McDonald said. "It supports the view that poor diets in pregnancy can alter development of fetal organs, in this case the brain, in ways that will have lifetime effects on offspring, potentially lowering IQ and predisposing to behavioral problems."

Developmental programming of lifetime health has been shown to play a role in later development of obesity, diabetes and heart disease.

In light of this new finding, the researchers said research should focus on effects of developmental programming in the context of autism, depression, schizophrenia and other brain disorders.

According to McDonald, the study also forces researchers to review the commonly held notion that during pregnancy the mother is able to protect the fetus from dietary challenges such as poor nutrition.

The study was published this week in Proceedings of the National Academy of Sciences.