Fetal Growth, Labor, & Postnatal Adjustments

afterbirth

Third stage of childbirth in which the placenta and associated fetal membranes are expelled.

allantois

Finger-like outpocketing of yolk sac forms the primitive excretory duct of the embryo; precursor to the urinary bladder.

amnion

Transparent membranous sac that encloses the developing fetus and fills with amniotic fluid.

amniotic cavity

Cavity that opens up between the inner cell mass and the trophoblast; develops into amnion.

Braxton Hicks contractions

Weak and irregular peristaltic contractions that can occur in the second and third trimesters; they do not indicate that childbirth is imminent.

brown adipose tissue

Highly vascularized fat tissue that is packed with mitochondria; these properties confer the ability to oxidize fatty acids to generate heat.

chorion

Membrane that develops from the syncytiotrophoblast, cytotrophoblast, and mesoderm; surrounds the embryo and forms the fetal portion of the placenta through the chorionic villi.

chorionic membrane

Precursor to the chorion; forms from extra-embryonic mesoderm cells.

chorionic villi

Projections of the chorionic membrane that burrow into the endometrium and develop into the placenta.

colostrum

Thick, yellowish substance secreted from a mother’s breasts in the first postpartum days; rich in immunoglobulins.

dilation

First stage of childbirth, involving an increase in cervical diameter.

ductus arteriosus

Shunt in the pulmonary trunk that diverts oxygenated blood back to the aorta.

ductus venosus

Shunt that causes oxygenated blood to bypass the fetal liver on its way to the inferior vena cava.

episiotomy

Incision made in the posterior vaginal wall and perineum that facilitates vaginal birth.

expulsion

Second stage of childbirth, during which the mother bears down with contractions; this stage ends in birth.

fetus

Developing human during the time from the end of the embryonic period (week 9) to birth.

foramen ovale

Shunt that directly connects the right and left atria and helps divert oxygenated blood from the fetal pulmonary circuit.

foremilk

Watery, translucent breast milk that is secreted first during a feeding and is rich in lactose and protein; quenches the infant’s thirst.

gestation

In human development, the period required for embryonic and fetal development in utero; pregnancy.

hindmilk

Opaque, creamy breast milk delivered toward the end of a feeding; rich in fat; satisfies the infant’s appetite.

involution

Postpartum shrinkage of the uterus back to its pre-pregnancy volume.

lactation

Process by which milk is synthesized and secreted from the mammary glands of the postpartum female breast in response to sucking at the nipple.

lanugo

Silk-like hairs that coat the fetus; shed later in fetal development.

let-down reflex

Release of milk from the alveoli triggered by infant suckling.

lightening

Descent of the fetus lower into the pelvis in late pregnancy; also called “dropping”.

lochia

Postpartum vaginal discharge that begins as blood and ends as a whitish discharge; the end of lochia signals that the site of placental attachment has healed.

meconium

Fetal wastes consisting of ingested amniotic fluid, cellular debris, mucus, and bile.

nonshivering thermogenesis

Process of breaking down brown adipose tissue to produce heat in the absence of a shivering response.

parturition

Childbirth.

placenta

Organ that forms during pregnancy to nourish the developing fetus; also regulates waste and gas exchange between mother and fetus.

placenta previa

Low placement of fetus within uterus causes placenta to partially or completely cover the opening of the cervix as it grows.

placentation

Formation of the placenta; complete by weeks 14–16 of pregnancy.

prolactin

Pituitary hormone that establishes and maintains the supply of breast milk; also important for the mobilization of maternal micronutrients for breast milk.

quickening

Fetal movements that are strong enough to be felt by the mother.

shunt

Circulatory shortcut that diverts the flow of blood from one region to another.

trimester

Division of the duration of a pregnancy into three 3-month terms.

true labor

Regular contractions that immediately precede childbirth; they do not abate with hydration or rest, and they become more frequent and powerful with time.

umbilical cord

Connection between the developing conceptus and the placenta; carries deoxygenated blood and wastes from the fetus and returns nutrients and oxygen from the mother

vernix caseosa

Waxy, cheese-like substance that protects the delicate fetal skin until birth.

yolk sac

Membrane associated with primitive circulation to the developing embryo; source of the first blood cells and germ cells and contributes to the umbilical cord structure.