Guidepost 1 What are the three stages of prenatal development, and what happens during each stage?

• Prenatal development occurs in three stages of gestation: the germinal, embryonic, and fetal stages.
• Growth and development both before and after birth follow the cephalocaudal principle (head to tail) and the proximodistal principle (center outward).
• About one-third of all conceptions end in spontaneous abortion, usually in the first trimester of pregnancy.

Guidepost 2 What can fetuses do?

• As fetuses grow, they move less, but more vigorously. Swallowing amniotic fluid, which contains substances from the mother's body, stimulates taste and smell. Fetuses seem able to hear, exercise sensory discrimination, learn, and remember.

Guidepost 3 What environment influences can affect prenatal development?

• The developing organism can be greatly affected by its prenatal environment. The likelihood of a birth defect may depend on the timing and intensity of an environmental event and its interaction with genetic factors.
• Important environmental influences involving the mother include nutrition, physical activity, smoking, intake of alcohol or other drugs, transmission of maternal illnesses or infections, maternal age, incompatibility of blood types, and external environmental hazards, such as chemicals and radiation. External influences also may affect the father's sperm.

Guidepost 4 What techniques can assess a fetus's health and well-being, and what is the importance of prenatal care?

• Ultrasound, amniocentesis, chorionic villus sampling, ambryoscopy, preimplantation genetic diagnosis, umbilical cord sampling, and maternal blood tests can be used to determine whether an unborn baby is developing normally. Some abnormal conditions can be corrected through fetal therapy.
• Early, high-quality prenatal care is essential for healthy development. It can lead to detection of defects and disorders and, especially if begun early and targeted to the needs of at-risk women, may help reduce maternal and infant death, low birthweight, and other birth complications.