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Pregnancy, the Brain and Child Development in the Third Trimester

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Your baby isn't just getting longer and gaining weight during the third trimester. During the last three months of pregnancy your soon-to-be-born baby's brain is developing at a quick pace, according to the University of Maryland Medical Center. The way you treat your own body, as well as genetic and environmental factors, influence your baby's third-trimester brain development.

You've Come a Long Way, Baby

A mere three weeks after conception your baby's brain starts to develop, according to Zero to Three, a nonprofit organization focused on early childhood development. From the bare and basic beginnings of the first trimester to the more complex third trimester, the brain is growing, gaining mass and achieving an almost infant-like ability to "think." This means that your growing fetus is able to see and hear, notes the Children's Hospital of Philadelphia. "Last of all to mature is the cerebral cortex, which is responsible for most of what we think of as mental life—conscious experience, voluntary actions, thinking, remembering, and feeling," Zero to Three explains.

Heightened Vulnerability

The rate at which a baby's brain grows increases dramatically during the third third trimester. "The weight of the brain roughly triples during the last 13 weeks of gestation, from an average of about (0.220462 pound) at the end of the second trimester to about (0.661387 pound) at full term, Harvard-Massachusetts General Hospital child neurologist Dr. Verne Caviness explained to writer Brenda Patoine. "This rapid development translates to heightened vulnerability to damage from both the internal (e.g., ischemia, inflammation, free-radical attack) and external (e.g., hormones, drugs, poor nutrition, etc.) environments," Patoine wrote in a briefing paper prepared for The Dana Foundation.

Alcohol and Risk

Drinking during pregnancy can cause a host of problems that fall under the fetal alcohol syndrome—or FAS—umbrella, according to the National Institute on Alcohol Abuse and Alcoholism. A steady pattern of consuming alcohol during the rapid brain growth time seen in the third trimester can cause an array of developmental problems that show up during infancy and the early years. These include, problems with visual-spatial leaning, language use, attention and focusing, reaction time and organizing or sequencing tasks, notes the National Institute on Alcohol Abuse and Alcoholism.

Brain and Behavior

The last three months of your pregnancy provide your child with the basic brain structure that he'll have throughout his life. Even though his genetic makeup provides him with a sort of blueprint for brain growth, it doesn't fully dictate how he'll progress as he develops after birth. Your baby's post-birth environment plays a pivotal role in where his brain goes from there, according to Zero to Three. While the third trimester may see growth and the development of new connections that go from brain region to region, the people and places that surround your baby after birth will impact his development.

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