Pregnancy and Childbirth
I. Terms
A. Pregnancy: events that occur from the time of fertilization until infant is born
B. Conceptus: developing offspring
1. Preembryo
a. Two weeks following fertilization
2. Embryo
a. 3rd through 8th weeks of development
3. Fetus
a. 9th week through birth
C. Gestation period: time during which development occurs
1. Length
a. 280 days
2. Onset
a. End of the previous menstrual
i. Pregnancy begins two weeks prior to fertilization
ii. Includes the follicular phase of the menstrual cycle
3. Embryonic period
4. Fetal period
II. Preembryonic Development
A. Fertilization to implantation
B. Events
1. Cleavage
2. Blastocyst production
3. Implantation of blastocyst
C. Cleavage and blastocyst production
1. Cleavage
a. Period of rapid mitotic divisions
b. Little growth
i. Daughter cells become smaller
2. Blastomeres
a. Identical daughter cells produced during the first 72 hours
3. Morula
a. 16+ cell stage
4. Blastocyst
a. Fluid-filled hollow sphere of a single layer of cells
b. 100 cells+
c. Preembryo free from zona pellucida
d. Trophoblast
i. Placenta formation
e. Inner cell mass
i. Becomes embryonic disc
ii. Forms the embryo
D. Implantation
1. Blastocyst floats freely in uterus for 2 – 3 days
2. About six days after fertilization implantation begins
3. Endometrium must be ready
a. Window of implantation
i. Ovarian hormones must be at appropriate levels
ii. Estrogen and progesterone
4. If endometrium is prepared, blastocyst implants high in the uterus
5. If endometrium is not ready, blastocyst continues to move lower in the uterus
a. Implants where chemical environment is appropriate
6. Outer layer (trophoblast) adheres to endometrium
7. Trophoblast invades the endometrium
a. Digests the uterine cells
b. Blastocyst burrows into endometrium
i. Surrounded by blood leaked from degraded endometrial blood vessels
c. Blastocyst is covered over and sealed off from uterine cavity
8. Implantation takes about a week
a. Completed by 14th day after ovulation
i. Corresponds to timing of menstruation
9. Implanted preembyo secretes a hormone to maintain corpus luteum
a. Human chorionic gonadotropin (hCG)
i. Causes corpus luteum to continue secreting progesterone
b. Conceptus takes over hormonal control of the uterus
i. High for the first two months of pregnancy
c. Pregnancy tests are used to detect hCG
10. Placenta will ultimately produce progesterone and estrogen to support uterus
a. Not until 3 –4 months
11. Nutrients for developing embryo initially comes from digested endometrial cells
a. By the second month, placenta provides nutrients
E. Placenta
1. Temporary organ
a. Made from both maternal and fetal sources
2. Embryonic tissue forms the inner part of the placenta
a. Chorion
i. Formed from trophoblastic tissue
ii. Fetal blood connects to maternal sources via chorion
iii. Do not intermix
iv. Materials diffuse between the two sources
3. Part of the endometrium becomes the deciduas basalis (see below)
4. Function of the placenta
a. Nutrition
b. Respiration
c. Excretion
d. Endocrine organ
5. Placental hormones are necessary for pregnancy
a. hCG maintains corpus luteum
i. Only temporarily
ii. 2-3 months
b. Placenta takes over much of the role of the ovaries after three months
i. Provides peptide and steroid hormones for maintenance of pregnancy
c. Hormones provided by placenta
i. hCG (functionally similar to LH)
ii. hCS (human chorionic somatomammotrophin
iii. Progesterone
iv. Estrogen
6. Function of hormones
a. hCS
i. Increases through pregnancy
ii. Necessary for the development of the breasts
b. Progesterone
i. Maintains the endometrium
ii. Levels reach a peak after about 3-4 weeks after fertilization
iii. Decline before increasing again up to the time of parturition
iv. Second increase is important for the development of the breasts
c. Estrogen
i. Necessary for the uterus to develop to accommodate the growing fetus
ii. Important for the latter stages of breast development
7. Placenta and mother’s body operate in concert
a. Placenta is an interface between mother and baby
b. It consists of both maternal and embryonic tissue
c. From third month to parturition it is the intermediary between mother and developing baby
F. Decidual reaction
a. Uterine endometrium changes rapidly when implantation occurs
i. This is called the decidual reaction
(* What is the origin and meaning of this term? Think of the way that some trees shed leaves in autumn. These are deciduous trees. The term originates from the Latin decidere which means ‘to fall off’ at some stage during the lifecycle. The endometrial tissues closely involved with the conceptus during pregnancy will be shed from the uterus at the time of birth and are thus called the deciduas. The changes triggered at the time of implantation are therefore called the decidual reaction.)
b. Endometrium accumulates glycogen and lipids
i. Glycogen is a storage form of glucose
ii. Mobilized to provide energy
c. Decidual reaction prepares the endometrium for pregnancy
G. Structure of the mature placenta
1. Dimensions at term
a. Diameter of approximately 20 cm
b. 3 cm thick
c. 500 g
2. Surface of the placenta facing the fetus has a shiny surface
3. Umbilical cord arises from the center of the fetal aspect of the placenta
a. Umbilical cord at term is about the same length as the baby
i. 50-60 cm
4. Maternal side of the placenta
a. Modified to permit nutrients and oxygen to be transferred from mother to baby
i. Blood does not mix
ii. If maternal and fetal blood cells were to mix, a maternal immune response would be initiated because the baby’s cells are genetically different from those of the mother
iii. This would result in the mother producing antibodies and cellular reactions against her baby’s tissues and damaging them
H. Umbilical cord
1. Three blood vessels
a. 2 umbilical arteries
i. Bring fetal blood to the placenta
b. 1 umbilical vein
i. Returns blood to baby’s heart
III. Embryonic Development
A. Blastocyst to gastrula
1. Fertilization
a. One cell
2. Preembryo
a. Morula
i. Multiple cells
ii. Inside zona pellucida
b. Blastocyst
i. Fluid-filled sphere of cells
ii. Free from zona pellucida
B. Embryonic membranes
1. Types
a. Amnion
b. Yolk sac
c. Allantois
d. Chorion
2. Functions
a. Amnion
i. Transparent membranous sac
ii. Becomes fluid-filled
iii. Extends around the embryo
iv. Protects against physical trauma
v. Prevents embryo parts from adhering to together
vi. Allows musculoskeletal development
vii. Initially derived from maternal blood
viii. Fetal urine contributes to amnionic fluid
b. Yolk sac
i. Sac hanging from embryo
ii. In other animals, yolk is the main source of nutrition
iii. In humans, placenta plays nutritive function
iv. Forms part of digestive tract
v. Produces earliest blood cells
vi. Source of primordial germ cells for gonads
c. Allantois
i. Becomes the umbilical cord that links embryo with placenta
ii. Becomes part of urinary bladder
d. Chorion
i. Helps form chorion
ii. Encloses all other membranes and embryo
C. Gastrulation
1. Two layered embryo to a three layered embryo
2. Primary germ layers
a. Ectoderm
b. Mesoderm
c. Endoderm
3. Function of gastrulation
a. Lays down basic structural framework of the embryo
b. Permits the development of tissues and organs
4. Fate of the primary germ layers
a. Ectoderm
i. Nervous system
ii. Skin epidermis
b. Endoderm (“inner skin”)
i. Epithelial linings of GI, respiratory and urogenital tracts
c. Mesoderm
i. Everything else
ii. Muscle
iii. Blood
iv. Bone
IV. Development of Fetal Circulation
A. Cardiovascular system
1. Begins to form during 3rd week following conception
2. Heart beat by week 3.5
B. Fetal modifications
1. Umbilical arteries and veins
a. Umbilical vein carries blood with oxygen and nutrients from placenta to embryo
i. Veins normally have low oxygen content
b. Umbilical arteries return waste-laden blood from fetus to placenta
c. Mother delivers oxygen and nutrient-rich blood to placenta
2. Vascular shunts
a. No need for blood to go through liver
i. Ductus venosus
ii. Mixes oxygen-rich blood with oxygen-poor blood
b. No oxygen from fetal lungs
c. Heart (overview blood flow)
i. Get oxygen-rich blood coming from placenta into systemic circulation
ii. Foramen ovale—shunt between right and left atria
iii. Ductus arteriosus—shunt blood from pulmonary trunk to aorta (bypassing pulmonary circuit)
V. Fetal Development
A. Weeks 9 through 40
1. Growth and differentiation
B. Dimensional changes
1. Start of fetal development
a. Crown-to-rump length
i. 30 mm (1 inch)
b. Weight
i. 1 g (0.03 oz)
2. At parturition
a. Crown-to-rump length
i. 360 mm (14 inch)
b. Weight
i. 2.7 – 4.1 kg (6 – 10 lb)
c. Length
i. 550 mm (22 in)
C. Developmental events of the fetal period
1. 8 weeks—end of embryonic period
a. Head equal to body length
b. Large liver
c. Limbs present
i. Webbed digits
d. Bones ossify
e. Cardiovascular system is functional
f. All body systems are present
2. 9 – 12 weeks—3rd month
a. Body elongates
b. Head is still disproportionately large
i. Brain continues to enlarge
c. Skin epidermis is formed
i. Crude facial features
d. Sex can be determined
e. Limbs well formed
f. Crown-to-rump length
i. 90 mm (3.5 inch)
3. 13 – 16 weeks—4th month
a. Nervous system continues to develop
i. Sensory organs are differentiated
ii. Eyes blink
iii. Sucking motions of lips
b. Face looks human
i. Body beginning to outgrow head
c. Crown-to-rump length
i. 140 mm (6 inch)
4. 17 – 20 weeks—5th month
a. Vernix caseosa covers body
i. Fatty secretions of sebaceous glands
b. Lanugo covers skin
i. Silk-like hair
c. Body is in the fetal position
i. Body too bid for space restrictions of uterus
d. Limbs reach final proportions
e. Quickening occurs
i. Mother feels spontaneous muscular activity of fetus
f. Crown-to-rump length
i. 190 mm (8 inch)
5. 21 – 30 weeks—6th and 7th months
a. Substantial weight increase
b. Survival is possible after week 27
i. Requires temperature regulation
ii. Requires ventilation
c. Eyes are open
d. Skin is red and wrinkled
e. Toenails and fingernails are present
f. Lean, well-proportioned body
g. Limb bones begin to ossify
h. Crown-to-rump length
i. 280 mm (12 inch)
6. 30 – 40 weeks—8th and 9th months (“Term”)
a. Skin is whitish pink
b. Fat in subcutaneous tissue
c. Crown-to-rump length
i. 360 - 400 mm (14 - 16 inch)
VI. Effects of Pregnancy on Mother
A. Anatomical changes
1. Progressive changes during pregnancy
a. Reproductive tract becomes more vascular and engorged with blood
i. Chadwick’s sign—vagina develops a purplish hue
ii. Vascularity increases vaginal sensitivity and sexual intensity
b. Breasts engorge
i. Effect of placental estrogen and progesterone
ii. Enlarge
iii. Areolae darken
c. Chloasma—pigmentation of facial skin of nose and cheeks
d. Uterine changes
i. Before fertilization, uterus is the size of a fist
ii. At four months, the fundus of the uterus is halfway between the pubic bone and the umbilicus
iii. At seven months, the fundus is above the umbilicus
iv. At 9 months, the fundus reaches the xiphoid process
2. Relaxin
a. Placental hormone
b. Pubic bones (3 fused bones) relax, widen and become more flexible
c. Eases birth passage
i. May result in a waddling gate
3. Weight gain
a. About 30 lb
i. Fetal and placental growth
ii. Maternal reproductive organs and breasts
iii. Increased blood volume
B. Metabolic changes
1. Placenta secretes hormones that affect maternal metabolism
a. hCS (human chorionic somatomammotropin) stimulates breasts to mature for milk production
b. hPL (human placental lactogen) stimulates the growth of fetus and causes a reduction in glucose use by maternal cells
i. Maternal cells use more fatty acids and amino acids
ii. Glucose is spared for fetal use
c. hCT—human chorionic thyrotropin increases rate of maternal metabolism
i. Hypermetabolism
ii. Appetite changes can be attributed to hCT
C. Physiological changes
1. Gastrointestinal system
a. Morning sickness
i. Response to elevated estrogen and progesterone levels early in pregnancy
b. Heartburn
i. Esophagus is displaced and the stomach is crowded by the growing uterus
ii. Acid is refluxed from stomach into esophagus
c. Constipation
i. Motility of GI tract declines during pregnancy
2. Urinary system
a. Kidney makes more urine
i. Kidneys need to clear fetal wastes in addition to maternal wastes
b. Growing uterus compresses bladder, making urination more frequent and urgent
c. Stress incontinence
i. Urination becomes uncontrollable
3. Respiratory system
a. Estrogen causes nasal mucosa to become congested
b. Vital capacity and respiratory rate increase during pregnancy
c. Residual volume declines
i. Breathing may become difficult
4. Cardiovascular system
a. Blood volume increase 25 – 40%
i. Acts as a safeguard against blood loss during birth
b. Blood pressure and heart rate increase by 20 – 40%
i. Propels a greater volume of blood around the body
c. Varicose veins
i. Uterus presses on pelvic blood vessels
ii. Impairs venous return from lower limbs
iii. Blood pools in vessels of legs
VII. Parturition—Birth
A. Timing
1. Within 15 days of calculated due date
a. 280 days following last menstrual cycle
B. Labor
1. Series of events that result in the expulsion of the fetus from the uterus
C. Initiation of labor
1. Not clearly understood
2. Associated with high levels of estrogen (why estrogen increases is not known)
a. Estrogen stimulates myometrial cells of the uterus to form oxytocin receptors
b. Estrogen offsets the effects of progesterone
3. Resultant effect is for myometrium to become increasingly irritable with intermittent and irregular, weak contractions
a. Braxtin Hicks contractions
i. False labor
4. Oxytocin is released by fetus
a. Source not presently known (i.e., which fetal cells)
5. Oxytocin acts on placenta which then releases prostaglandins
6. Oxytocin and prostaglandins are uterine muscle stimulants
7. Physical and emotional stress activate hypothalamus
a. Posterior pituitary releases oxytocin in response to hypothalamic activation
8. Oxytocin release is controlled by positive feedback
a. Increasing muscle contraction in response to oxytocin causes the release of more oxytocin
VIII. Stages of Labor
A. Stage 1: Dilation stage
1. Labor onset until full dilation of the cervix
a. Longest phase
b. 6 – 12 hours
2. Events
a. Upper part of uterus begins to contract
i. 15 – 30 minutes apart
ii. Duration: 10 – 30 seconds
b. Contractions become more vigorous and rapid
c. Lower uterine segments become involved
d. Baby’s head is forced against cervix with each contraction
i. Cervix softens
ii. Cervix becomes thinner (effaces)
iii. Cervix dilates (diameter of opening increases)
e. Amnion ruptures—breaking the water
i. Amnionic fluid is released
f. Engagement
a. Infant’s head enters true pelvis
i. Head is aligned so its greatest dimension is along anterior-posterior line
B. Stage 2: Expulsion stage
1. From full dilation until the infant is delivered
2. Contractions
a. Every 2 – 3 minutes
b. 1 minute apart
3. Without anesthesia the mother has an urge to bear down (push)
4. Length of the phase
a. First birth
i. 50 min
b. Second birth
i. 20 min
5. Crowning
a. Largest diameter of the baby’s head is distending the vulva
b. Episiotomy—incision made to widen vaginal orifice
i. Incision between vaginal opening and anus
6. Presentation
a. Vertex: head first
i. Head acts as a wedge against cervix
b. Non-vertex (e.g., breech): non-head first
7. Dystocia
a. Prolonged, difficult birth
C. Stage 3: Placental stage
1. Delivery of the placenta
a. Within 30 minutes of the birth
2. Uterus continues to contract
a. Compress blood vessels
i. Limits bleeding
b. Causes placenta to be detached from uterine wall
3. Afterbirth
a. Placenta and fetal membranes
4. Postpartum bleeding
a. Continued uterine bleeding after birth
IX. Transition to Extrauterine Life
A. Neonatal period
1. First four weeks
2. Birth is a very stressful experience for both the infant and mother
a. Transition from warm, homeostatic aqueous environment
i. No respiration
ii. Nutrients provided
iii. Limited excretion
iv. Constant body temperature
B. Apgar score
1. Infant’s physical status is ranked 0 – 2 on five signs
a. Heart rate
b. Respiration
c. Color
d. Muscle tone
e. Reflexes
C. First breath
1. Increase in CO2 causes chemical acidosis
2. This activates respiratory control centers to trigger breathing
3. First breath is difficult
a. Lungs are collapsed
4. Once inflated, breathing is much easier
D. Transitional period
1. 6 – 8 hours after birth
2. Adjust to extrauterine life
a. Awake first 30 minutes
b. Heart rate elevated above normal fetal range
i. 120 –160 beats/sec
c. Respiration rate increases and becomes irregular
d. Body temperature falls
e. Activity diminishes
f. Baby sleeps for 3 hours
g. Second period of activity occurs
i. Gags and regurgitates mucus and debris
h. Baby sleeps and stabilizes
i. Waking periods dictated by hunger
i. 3 – 4 hours
X. Lactation
A. Production of milk by mammary glands
1. Hormonal changes at end of pregnancy stimulate the hypothalamus
a. Placental estrogen, progesterone and lactogen increase
b. Hypothalamus releases PRH—prolactin releasing hormone
c. PRH acts on anterior pituitary
i. Prolactin is secreted
2. During first few days following birth
a. Colostrum is secreted from mammary glands
i. Not true milk
ii. Less lactose (sugar)
iii. No fat
iv. More protein, vitamin A and minerals
v. Rich in antibodies
3. Prolactin release gradually decreases without mechanical stimulation of the nipples
a. Nervous connection from nipple to hypothalamus
i. Stimulate PRH release
b. Prolactin is released
i. Stimulates milk production for next feeding
4. Same nervous impulse also activates oxytocin release from posterior pituitary
a. Let-down reflex
i. Ejection of milk from the alveoli of the mammary gland (from both breasts)
5. Benefits of breast finding
a. Oxytocin also acts on smooth muscle of the uterus
i. Causes uterine contraction and return to pre-pregnancy proportions
b. Nutrients of maternal milk are more readily absorbed and metabolized than cow’s milk
c. Beneficial chemicals uniquely present in maternal milk
i. Antibodies
ii. Other immune products
d. Acts as a natural laxative
i. Cleanses meconium from bowels
XI. Ectopic Pregnancy
A. Definition
1. Ectopic: out of place
B. Ectopic pregnancy
1. Non-uterine pregnancy
a. Ampullary (mid) portion of the fallopian tube (80-90%)
b. Isthmic (area closer to the uterus) portion of the fallopian tube (5-10%)
c. Fimbrial (distal end away from the uterus) portion of the fallopian tube (5%)
d. Cornual (within the uterine muscle) portion of the fallopian tube (1-2%)
e. Abdomen (1-2%)
f. Ovary (less than 1%)
g. Cervix (less than 1%)
C. Ectopic pregnancies are dangerous
1. Pregnancy a large nutrient source (blood supply) and develops many communications with the mother's vascular system (blood vessels)
2. Uterus is uniquely designed to accommodate this development
3. When a pregnancy begins to grow in other surrounding structures the vascular communication may be inadequate
D. During normal pregnancy, uterus dramatically changes shape and size
1. Other non-uterine structures are usually not able to change as readily
a. Ruptured or damaged
2. When the ectopic pregnancy outgrows the limits of the space enclosing it, there can be life threatening bleeding
E. Risk factors for ectopic pregnancy
1. Prior history of ectopic pregnancy
2. History of surgery on the fallopian tubes or within the pelvis
3. History of pelvic infection
4. Use of assisted reproductive technology (such as IVF and GIFT)
a. Multiple embryos or gametes are replaced into the uterus or the fallopian tubes, the risk for multiple pregnancy rises significantly
i. Risk of a heterotopic pregnancy (twins with one pregnancy in the uterus and one in the fallopian tube): 1/100 vs. 1/30,000
5. History of IUD use
6. History of non-infectious pelvic inflammation (endometriosis, foreign body).
F. Three primary types of treatment
1. Surgical management
2. Medical management
3. Expectant management