Your baby’s brain starts developing almost at the moment of conception, according to the Long Island Spectrum Center website. By the time you are three weeks pregnant, the developing embryo has formed a neural groove, which is the foundation for the brain structure. By the time your baby is born, her brain will have over 100 billion neurons.

First Trimester

The brain grows at a remarkably rapid rate. By the end of the third week of gestation, the embryo has formed the three parts of the brain (the forebrain, midbrain and hindbrain). One week later, the brain begins functioning. At this point, the brain busily begins to work on the placement of all the major organs and systems. By the end of the eighth week of pregnancy, all of the major organs are in place, according to the Long Island Spectrum Center website.

Second and Third Trimester

By the start of the second trimester of pregnancy, all of the major structures of the brain are in place and functioning. From this point forward, the brain and major organs continue to develop and mature. The brain connects to all parts of the body during this time, and the connections are complete by the seventh month, in a process known as synaptogenesis. The brain is also making other connections: Rapid brain and head growth occurs during the eighth month. According to ABC News, babies in the womb are known to be able to recognize their mother’s voice at this point.

Aggregation

As the brain is formed, cells are being placed precisely where they need to go in a process called aggregation. As the fetal brain develops, cells are organized in proper directions and layers, but sometimes this process goes awry. Abnormal cell aggregation in the brain can be caused by genetic or external factors such as poor maternal health habits such as drinking alcohol or using drugs. In addition, studies show that chronic stress in the mother-to-be can affect the brain development of the baby, according to Quantum Parenting.

Fetal Alcohol Syndrome

Babies born with fetal alcohol syndrome, the primary known preventable cause of mental retardation, have measurable differences in brain structure. Cerebellum size, as well as other crucial brain structures involved in cognition, balance and coordination, are compromised, according to the National Institute on Alcohol Abuse and Alcoholism. In babies with FAS, incidence of a damaged or absent corpus callosum, the nerve tissue that connects the two halves of the brain, is about 20 times more common than in the babies of non-drinking mothers. The process by which alcohol damages the fetus is still being studied, but present research suggests that alcohol increases the brain’s vulnerability to specific cell damage from free radicals, notably in the first trimester, as well as further damage throughout the third trimester. NIAAA director Enoch Gordis, M.D., states that research has yet to determine a “safe” level of alcohol consumption and recommends abstinence from all alcoholic beverages throughout pregnancy for complete safety.

Problems for Premies

Your baby’s brain continues to develop after birth. Babies born prematurely, however, have compromised brains that may not develop as readily as babies who are born full-term, according to Science Daily. This is thought to be in part due to the large amount of stimuli premature babies experience, which is much different that babies born full-term. Full-term babies have brains that finish their development in the dark, quiet environment of the womb. A study by doctors at Imperial College London published in the peer-reviewed journal “PLoS Medicine” measured the surface area and volume of the brains of babies born between the 22nd and 29th week of gestation. Including subsequent measurements at the 48th week and cognitive tests at two years old, the study found that in premies, the brain’s surface area grows faster than its volume. The babies that were most premature had the slowest rate of surface-area brain growth compared to the growth of brain volume, accompanied by the most serious delays noted in cognitive testing.

Baby Development in the Womb