Beginning of pregnancy
Pregnancy begins at conception, which is also the starting point of gestational age. However, the organism does not become an embryo until about two weeks later, and pregnancy does not affect the woman (and cannot be confirmed by blood or urine testing) u
Length of pregnancy
Full-term pregnancies last 266 days, or 38 weeks, or 9 months.
Trimesters
Instead of germinal period, embryonic period, and fetal period, some writers divide pregnancy into three-month periods called trimesters.
Due date
Although doctors assign a specific due date (based on the woman's LMP), only 5% of babies are born on that exact date.
implantation
The process beginning about 10 days after conception, in which the developing organism nestles in, and attaches to the placenta that lines the uterus.
Brain
As nerves and muscles form links to the brain, the embryo now moves spontaneously, as the brain begins to move muscles.
Facial features
Eyes and eyelids are developed. Eyes will continue to migrate to the front of the head, where they will eventually rest. Eyelids begin to grow together and are only half closed. External, middle, and inner ears are now fully formed. External ears will con
Arms, hands, and fingers
Arms are well formed, longer, and can bend at elbows and move forward. Fingers elongate and digits are fully separated. Each finger has three digits, and the thumb has two digits.
External sex organs
Urogenital membranes have developed into either male or female organs, and ovaries or testicles are visible. Clitoris or penis begins to form, but distinguishing the embryo's sex is difficult.
Intestines
The intestines begin to move from the umbilical cord to the embryo's body cavity.
Overall appearance
The head is still disproportionately large but is erect and appears rounded. The neck is well defined. The tail will disappear by the end of this week. Cartilage begins to turn into bone. The ectoderm layer is replaced by the beginnings of skin. The body
fetus
A developing human organism from the start of the ninth week after conception until birth.
Germinal period
At least 60 percent of all developing organisms fail to grow or implant properly and thus do not survive the germinal period. Most of these organisms are grossly abnormal.
Embryonic period
About 20 percent of all embryos are aborted spontaneously*, most often because of chromosomal abnormalities.
Fetal period
About 5 percent of all fetuses are aborted spontaneously before viability at 22 weeks or are stillborn, defined as born dead after 22 weeks.
Birth
About 31 percent of all zygotes grow and survive to become living newborn babies.
Apgar scale
A quick assessment of a newborn's health, given twice (at one minute and five minutes after birth).
Low Birth Weight (LBW)
A body weight at birth of less than 5 � pounds (2,500 grams).
Very Low Birth Weight (VLBW)
A body weight at birth of less than 3 pounds, 5 ounces (1,500 grams).
Extremely Low Birth Weight (ELBW)
A body weight at birth of less than 2 pounds, 3 ounces; (1,000 grams).
Why is birth weight important?
Lagging physical and cognitive development confronts babies born early (or preterm, once called premature), and a preterm baby also is probably low birth weight.
reflex
An unlearned, involuntary action or movement in response to a stimulus.
What are some newborn reflex experiences?
Breathing, sucking, stepping, and moro
couvade
Symptoms of pregnancy and birth experienced by fathers.