| embryo | In humans, the developing offspring
in utero from about the beginning of the third
week to the end of the eighth week after
conception.
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| ovum | The egg cell from which a fetus
eventually develops if the egg is fertilized by
a sperm cell.
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| fetus | The developing life form from about
the beginning of the ninth week after conception
until birth.
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| placenta | An organ that forms in the uterus
in pregnant women. Through this organ,
oxygen and nutrients from the mother’s
blood are transferred to the fetus, and fetal
wastes are removed. The placenta also releases
hormones that maintain the state
of pregnancy.
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| zygote | The fertilized ovum; the cell resulting
from the union of an egg cell (ovum) and
sperm until it divides.
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| trimesters | Three 13- to 14-week periods
into which the normal pregnancy of 38 to
42 weeks is divided somewhat arbitrarily for
purposes of discussion and analysis. Development
of the offspring, however, is continuous
throughout pregnancy, with no specific
physiological markers demarcating the
transition from one trimester to the next.
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| spontaneous abortion | Cessation of pregnancy
and expulsion of the embryo or nonviable
fetus prior to 20 weeks gestation. This is
the result of natural causes, such as a genetic
defect or developmental problem; also called
miscarriage.
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| lactation | The period of milk secretion following
pregnancy; typically called breastfeeding.
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| gestation | The period of intrauterine development
of offspring, from conception to
birth; in humans, gestation lasts for about
40 weeks after the woman’s previous
menstrual period.
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| low birth weight (LBW) | Referring to any
infant weighing less than 2.5 kilograms
(5.5 pounds) at birth; most commonly results
from preterm birth.
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| preterm | An infant born before 37 weeks of
gestation; also referred to as premature.
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| small for gestational age (SGA) | Referring
to infants who weigh less than the expected
weight for their length of gestation. This
corresponds to less than 2.5 kilograms
(5.5 pounds) in a full-term newborn. A
preterm infant who is also SGA will most
likely develop some medical complications.
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| pica | The practice of eating nonfood items,
such as dirt, laundry starch, or clay.
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| menarche | The onset of menstruation.
Menarche usually occurs around age 13, 2
or 3 years after the first signs of puberty start
ot appear.
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| fetal alcohol syndrome (FAS) | A group of
irreversible physical and mental abnormalities
in the infant that result from the mother’s
consuming alcohol during pregnancy.
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| fetal alcohol effect (FAE) | Hyperactivity,
attention deficit disorder, poor judgment,
sleep disorders, and delayed learning as a
result of prenatal exposure to alcohol.
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| physiological anemia | The normal increase
in blood volume in pregnancy that dilutes the
concentration of red blood cells, resulting in
anemia; also called hemodilution.
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| gestational diabetes | A high blood glucose
concentration that develops during pregnancy
and returns to normal after birth; one cause is
the placental production of hormones that
antagonize the regulation of blood glucose by
insulin.
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| pregnancy-induced hypertension | A
serious disorder that can include high blood
pressure, kidney failure, convulsions, and even
death of the mother and fetus. Although its
exact cause is not known, an adequate diet
(especially adequate calcium intake) and
prenatal care may prevent this disorder or
limit its severity. Mild cases are known as
preeclampsia; more severe cases are called
eclampsia (formerly called toxemia).
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| lobules | Saclike structures in the breast that
store milk.
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| prolactin | A hormone secreted by the
mother that stimulates the synthesis of milk.
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| let-down reflex | A reflex stimulated by infant
suckling that causes the release (ejection)
of milk from milk ducts in the mother’s
breasts; also called milk ejection reflex.
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| oxytocin | A hormone secreted by the pituitary
gland. It causes contraction of the musclelike
cells surrounding the ducts of the breasts and
the smooth muscle of the uterus.
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| colostrum | The first fluid secreted by the
breast during late pregnancy and the first
few days after birth. This thick fluid is rich
in immune factors and protein.
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| Lactobacillus bifidus factor | A protective
factor secreted in the colostrum that encourages
growth of beneficial bacteria in the
newborn’s intestines.
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