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zygote  The developing organism from the time of the union of sperm and egg to about the second week of gestation; the period of the zygote comprises the implantation of the fertilized egg in the wall of the uterus.
embryo  The developing organism between the second and eighth week of gestation; the period of the embryo comprises the differentiation of the major physiological structures and systems.
amniotic sac  A membrane containing a watery fluid that encloses the developing organism, protecting it from physical shocks and temperature changes.
placenta  A fleshy, disclike structure formed by cells from the lining of the uterus and from the zygote, and that, together with the umbilical cord, serves to protect and sustain the life of the growing organism.
umbilical cord  A tube that contains blood vessels going between the growing organism and its mother by way of the placenta; carries oxygen and nutrients to the growing infant and removes carbon dioxide and waste products.
fetus  The developing organism from the third month of gestation through delivery; during the fetal period development of bodily structures and systems becomes completes.
lanugo  A fine, soft hair that covers the fetus's body from the fifth month of gestation on; may be shed before birth or after.
respiratory distress syndrome  A condition of the newborn marked by labored breathing and a bluish discoloration of the skin or mucous membranes and which often leads to death.
age of viability  The age of 22-26 weeks from conception by which point the fetus's physical systems are well enough advanced that it has a chance at survival if born prematurely.
teratogen  An environmental agent, such as a drug, medication, dietary imbalance, or polluting substance, that may cause developmental deviations in a growing human organism;
Rh factor incompatibility  A condition in which an infants Rh negative blood opposes its mother's Rh positive blood and threatens fetuses in second, third, and later births when the mother's body has had time to produce antibodies that will attack fetal blood cells.
toxoplasmosis  A parasitic disease transmitted from eating undercooked meat or handling cat litter, can cause eye and brain damage in a developing baby.
gonorrhea  A sexually transmitted bacterial infection that, in a pregnant woman, can cause blindness in her infant; normally treatable with antibiotics.
chlamydia  Probably the most widespread bacterial sexually transmitted disease; can cause pneumonia or a form of conjunctivitis in a pregnant woman's baby.
genital herpes  A common viral infection spread through sexual contact; if contracted by an infant during birth can cause blindness, motor abnormalities, mental retardation, and a wide range of neurological disorders.
Acquired Immune Deficiency Syndrome (AIDS)  A viral disease that attacks the body's immune systems; transmitted to a fetus or newborn in the form of human immunodeficiency virus (HIV), this disorder weakens the child's immune system and may ultimately cause its death.
fetal alcohol syndrome  A disorder exhibited by infants of alcoholic mothers and characterized by stunted growth, a number of physical and physiological abnormalities and, often, mental retardation.
diethylstibestrol (DES)  A synthetic hormone once prescribed for pregnant women
thalidomide  A drug once prescribed to relieve morning sickness in pregnant women but discontinued when found to cause serious malformations of the fetus.
anoxia  A lack of oxygen in brain cells
preterm  A term describing a premature baby who is born before its due date and whose weight, though less than that of a full-term infant, may be appropriate to its gestational age.
small for date  A term describing a premature baby who may be born close to its due date but who weighs significantly less than would be appropriate to its gestational age.

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