First Trimester

First month (starting with mother’s last menstrual period)

At the moment of conception, the new life has the complete genome of unique DNA the baby will have at birth and beyond. Gender, hair and eye color and other inherited characteristics are determined at this time. Unless specified as after conception, the weeks are counted from the date of last menstrual period which is usually two weeks prior to conception. So by the end of the “first month,” the embryo is usually two weeks after conception. This stage has its most rapid rate of growth and development. The heart and circulatory system is developing. The heart beats at day 18 after conception, and pumps blood by 21 days. The neural tube is formed that will develop into the nervous system. At the end of the first month, the length is approximately a tenth of an inch.

Second Month

The umbilical cord develops that pumps oxygen and nutrients to the baby and removes waste. Lungs and brain begin to develop. Brain waves have been recorded as early as 40 days after conception on EEG. Arm and leg buds appear and progressively grow, then elbows, fingers and toes that are initially webbed and short. Lenses of the eyes and nostrils appear, then the rest of the eyes and nose. The intestines grow within the umbilical cord initially, but by the end of the second month it is into the abdomen. The pancreas is forming. Teeth and tongue begins to develop. Cartilage and bones begin to form, and he muscles are developed enough that the embryo swims gracefully. By eight weeks, all body systems are present (by 11 weeks they all function).. At this point, the embryo is roughly ½ inch long and weighs about .04 ounce.