embryo implants in the uterus
cleavage, gastrulation, and neurulation occur
lungs mature and produce increasing amounts of surfactant
fetus becomes large enough to survive outside of the mother
fetus measures 12 inches long and weighs approx. 600 grams

corpus luteum degenerates; placenta takes over production of estrogen and progesterone

fetal heartbeat usually becomes audible
first trimester
second trimester
third trimester
early reflexes (ex. suckling) develop
nervous system begins to develop
little growth, but much differentiation occurs
the placenta forms

major organs begin to form, including the eyes, heart, liver, pancreas, and gallbladder

bones get bigger, muscles develop, and kicks can be felt by the mother

significant development of the nervous system (new neurons added at the rate of 15 million per hour!)

first trimester
second trimester
third trimester
Order of Events (First Month, First Trimester)
1.
the placenta forms
2.
eyes and heart begin to form
3.
gastrulation begins
4.
embryo reaches uterus for implantation
5.
neurulation begins
6.
cleavage begins
liver, pancreas, and gallbladder can be seen
embryo weighs approx. 1 gram
early reflexes (such as suckling) begin

placenta takes over production of estrogen and progesterone after corpus luteum disintegrates

limbs take shape
nervous system develops
month 2
month 3