CH. 28 - Pregnancy and Childbirth

Gestation

Pregnancy

• Lasts an average of 266 days from conception to childbirth

• Gestational calendar is measured from first day of the woman’s last menstrual period (LMP)

• Birth is predicted 280 days (40 weeks) from the first day of the last menstrual period

• The bigger the baby, the longer the gestation time

Term

The duration of pregnancy

Trimesters

three 3-month intervals in the term

Conceptus

all the products of conception

• the embryo or fetus, the placenta, and associated membranes

Blastocyst

The developing individual is a hollow ball for the first 2 weeks

• blastocyst is the individual before implanting into the endometrium

Embryo

From day 16 through week 8

• blastocyst becomes and embryo once it implants into the endometrium

Fetus

from beginning of week 9 to birth

• Fetus us attached to a disc-shaped placenta by the umbilical cord

  • placenta provides nutrition and waste disposal, secretes hormones that regulate pregnancy, mammary development, and fetal development

• before placenta is formed and the baby is a fetus, the baby gets nutrients from uterine glands

Neonate

newborn to 6 weeks

Hormones with strongest influence on pregnancy:

• Estrogens

• Progesterone

• Human chorionic gonadotropin

• Human chorionic somatomammotropin

Where are these hormones secreted from during pregancy?

All are primarily secreted by the placenta

• Corpus luteum is important source for first several weeks

  • If corpus luteum ia removed before 7 weeks, pregnancy terminates

• From week 7 to week 17, the corpus luteum degenerates and the placenta takes over

Human Chorionic Gonadotropin (HCG)

• Secreted by the blastocyst and placenta

• Detectable in urine 8 to 9 days after conception by home pregnancy test kits

• Stimulates growth of corpus luteum and keeps it around longer than normal

• HCG comes from the chorion of the embryo, travels to gonads, and causes them to release more progesterone and estrogen

Estrogens

• estrogen skyrockets during pregnancy

  • Increases to 30 times the normal amount by the end of pregnancy

• Corpus luteum is the source for first 12 weeks until placenta takes over

• Helps maintain endometrium

• Causes tissue growth in fetus and mother

  • Mother’s uterus and external genitalia enlarge

  • Mammary ducts grow, breast tissue nearly doubles in size

• higher estrogen increases relaxin, which relaxes pubic symphysis and widens pelvis

• Higher estrogen, higher libido

Progesterone

• Secreted by placenta and corpus luteum

• Suppresses FSH and LH, preventing follicular development during pregnancy so we aren’t growing multiple babies at different stages

• Suppresses uterine contractions

  • This prevents premature childbirth and menstruation

• Causes endometrium to get thicker

  • is important bc the endometrium is eaten by the blastocyst for nutrients in the beginning stages of pregnancy before placenta is formed

• Stimulates development of alveoli in mammary glands

• progesterone starts to drop at very end of third trimester, allowing for labor and delivery

Human Chorionic Somatomammotropin (HCS)

• Comes from the chorion and causes another gland to make secretions

• is basically a low level human growth hormone

• Placenta begins its secretion of HCS at about week 5

• Amount secreted increases steadily until term 

• There is a high concentration of HCS but the function is poorly understood

• causes babies tissues to differentiate

• also cause mothers tissues to differentiate

• also makes mother less sensitive to insulin bc they need more glucose in blood for baby

  • sometimes theres too much HCS, causing pregnancy induced diabetes

    • will go away when HCS level goes down (usually when giving birth)

What happens the pituitary gland during pregnancy?

Woman’s pituitary gland grows about 50% larger during pregnancy

• Produces elevated levels of thyrotropin, prolactin, and ACTH

  • these stimulate thyroid, lactate production, and salt retention

What happens to the thyroid gland during pregnancy?

Thyroid gland becomes 50% larger due to HCG, thyrotropin, and human chorionic thyrotropin from placenta

• Increases metabolic rate of mother and fetus

• This elevation is going to cause mother to feel like she is overheating

What happens to the parathyroid glands during pregnancy?

Parathyroid glands enlarge and increase osteoclast activity

• causes there to be more parathyroid hormone, leading osteoclasts to be unregulated

• this causes more calcium and phosphate to be put into blood stream

ACTH

• Causes there to be a lot of salt retention

• Stimulates glucocorticoid secretion

  • This breaks down and mobilizes amino acids for fetal protein synthesis

Aldosterone

Aldosterone secretion rises

• promotes fluid retention and increases mother’s blood volume

Relaxin

• Relaxin is secreted by corpus luteum and placenta

• It helps progesterone in stimulating multiplication of uterine lining cells

• Promotes growth of blood vessels in the pregnant uterus

• Loosens connective tissues

How much does the uterus weigh pregnant vs. not pregnant? How far does the uterus expand during pregnancy?

• Uterus weighs about 900 g at the end of pregnancy

• Weighs only 50 g when not pregnant

• Uterus expands up to the diaphragm when pregnant, almost reaching the xiphoid process

Linea Nigra

some mothers will experience an up regulation of melanocytes, causing more pigment right through the midsagittal plane of abdomen

Position of the baby in utero and during birth:

• during pregnancy, the baby is typically sitting head right side up

• In the 7th month of gestation, the fetus normally turns into the head-down vertex position

• Most babies are born head first

  • Head acting as a wedge that widens the mother’s cervix, vagina, and vulva during birth

  • breach - when baby tries to be born in a non head first way

Role of baby during birth:

Fetus is a passive player in its own birth

• Expulsion achieved by contractions of mother’s uterine and abdominal muscles

• Fetus may play a role chemically by releasing stress hormones to help enhance uterine contractions

• Fetus sends chemical messages that signify when it is developed enough to be born

Braxton Hicks Contractions

Relatively weak contractions of the uterus over the course of gestation

• Strengthen late in pregnancy

  • often causes false labor

• During third trimester, there is still elevated progesterone, so it will down-regulate the uterine contractions so there isn't early delivery

• Contractions transform suddenly into more powerful labor contractions, leading to active labor

Parturition

The process of giving birth

• Marked by the onset of true labor contractions

Uterine Contractility

Contractility increases closer and closer to birth of child

• As the uterus gets bigger and stretched, there will be more spontaneous contractions

• they help to strengthen the smooth muscle of uterus

• Progesterone and estradiol balance may be one factor in this pattern o

  • Progesterone inhibits uterine contractions, but its secretion levels off or declines after 6 months

  • Estradiol stimulates uterine contractions, and continues to rise through pregnancy

Oxytocin (OT)

As pregnancy nears full term, the posterior pituitary releases more oxytocin (OT), and the uterus produces more OT receptors

• Oxytocin promotes labor in two ways

  • stimulates contraction of smooth muscle, affecting myometrium of uterus

  • Stimulates fetal membranes to produce prostaglandins, which help oxytocin in producing labor contractions

    • prostaglandins dilate the cervix

How does the conceptus help promote its own birth?

Conceptus (placenta and fetus) may produce chemical stimuli to promote its own birth

• Fetal cortisol rises and may increase estrogen secretion by the placenta

• Fetal pituitary produces oxytocin, which stimulates fetal membranes to produce prostaglandin and start uterine contractions

How does uterine stretching help initiate labor?

Stretching of smooth muscle increases contractility of smooth muscle

• as the uterus stretches and contracts, more oxytocin is released, causing more contractions, causing more oxytocin

  • positive feedback loop

Labor Contractions (timing, where they are, where they are strongest/weakest, etc)

• Labor contractions begin about 30 minutes apart and eventually occur every 1 to 3 minutes

• Periodically relax to increase blood flow and oxygen delivery to placenta and fetus

• Contractions are strongest in fundus and body of uterus

• Contractions are weakest in the cervix

• Contractions push the fetus downward

• Woman feels need to “bear down”

  • Contraction of abdominal muscles aids in expelling the fetus (valsalva maneuver)

Positive Feedback Theory of Labor

• Labor is induced by stretching of cervix from baby’s head

• This triggers a reflex contraction of the uterine body

• the contraction pushes the fetus downward

• This stretches the cervix even more

• Creates a self-amplifying cycle of stretch and contraction

What does cervical stretching cause?

Cervical stretching induces a neuroendocrine reflex that causes the posterior pituitary to release oxytocin

• oxytocin is carried by the blood and stimulates uterine muscles to contract

  • Directly and through the action of prostaglandin

• Cervical stretching → oxytocin secretion → uterine contraction → cervical stretching

What is given for induced labor?

Pitocin

• artificial oxytocin

What causes the pain during labor contractions?

• At first, pain of labor is mainly due to ischemia (cut off blood supply) of the myometrium

  • Muscles hurt when they are deprived of blood, and contractions restrict circulation

• As fetus enters vagina, pain becomes stronger due to the stretching of the cervix, vagina, and perineum

  • sometimes with tearing

• Pain is a product of two factors

  • Unusually large brain and head of the human infant

  • Narrow pelvic outlet

Episiotomy

an incision in the vulva to widen the vaginal orifice to prevent random tearing

• not always done

3 Stages of Labor

1. Dilation

2. Expulsion

3. Placental stage

Primipara

Woman giving birth for the first time

• stages of labor tend to be longer

Multipara

Woman who has previously given birth

• stages of labor tend to be shorter

Grandmultipara

Woman who has previously given birth five times or more

Dilation Stage

• the longest stage

  • lasting 8 to 24 hours

• Cervical canal dilates to 10 cm

• effacement (thinning) of cervix occurs

• Fetal membranes rupture and amniotic fluid is lost

  • “water breaking”

• Late dilation

  • dilation reaches 10 cm in 24 hours or less in primipara and in as little as a few minutes in multipara

How to measure dilation:

each finger that fits into cervix is 1 cm

• feel for lip of cervix to feel for 10 cm

• cervix lip will be a little nub at the edge of uterus when fully dilated

Expulsion Stage

begins with the entry of the head into vagina and lasts until the baby is expelled

• 30-60 minutes in primipara; shorter in multipara

• Crowning occurs — when baby’s head is visible

  • Delivery of the head is the most difficult part

• After expulsion, doctor drains blood from umbilical vein into baby

  • Umbilical cord is clamped and cut

Placental Stage

uterine contractions cause placental separation and “delivery”

• Membranes (called the afterbirth) are inspected to make sure everything has been expelled

Puerperium

The first 6 weeks postpartum (after birth)

• Period where mother’s anatomy and physiology stabilize and reproductive organs return nearly to pregravid state (pre-pregnancy state)

• Involution occurs

Involution

shrinkage of the uterus in the first 6 weeks postpartum

• Loses 50% of its weight in the first week

• Involution is achieved by autolysis (self-digestion) of uterine cells by their own enzymes

• For about 10 days, the mother produces a vaginal discharge, called lochia

  • is bloody at first and then turns serous (clear)

What promotes involution of the uterus?

Breast-feeding promotes involution

• Suppresses estrogen secretion which normally makes the uterus more flaccid

• Stimulates oxytocin secretion which causes the myometrium to contract and firm up the uterus sooner

Lactation

the synthesis and ejection of milk from the mammary glands

• Lasts as little as 1 week in women who do not breast-feed their infants

• Can continue for many years as long as the breast is stimulated by a nursing infant or a mechanical device

• Women traditionally nursed their infants until a median age of about 2.8 years, now its about 6 months

Development of the Mammary Glands

• When not pregnant, mammary glands are small and not developed

• High estrogen levels in pregnancy causes ducts of mammary glands to grow and branch

• Growth hormone, insulin, glucocorticoids, and prolactin contribute to this development

• Progesterone stimulates the budding and development of acini at the end of the ducts

• Acini are organized into lobules within each breast lobe

  • one acini per lobe 

  • each have their own duct that leads to the nipple
    

Colostrum

Similar to breast milk in protein and lactose, but contains a lot more fat

• forms in late pregnancy

• is the sole nutrition source for first 1 to 3 days after birth

• Thick consistency and a cloudy yellow color

• Contains IgA to protect baby from gastroenteritis

• converting to colostrum to regular breast milk is a gradual process

  • the more the child consumes, the more the mother produces

• as more breast milk is produced, it becomes more diluted

Prolactin

Promotes milk synthesis

• from anterior pituitary

• Inhibited by dopamine when not pregnant

• Synthesis of prolactin begins 5 weeks into pregnancy, by full term it is 10 to 20 times the normal level

• Has little effect on mammary glands until after birth since steroids from placenta down regulate mammary glands

• Milk synthesis also requires growth hormone, cortisol, insulin, and parathyroid hormone to mobilize necessary amino acids, fatty acids, glucose, and calcium

Prolactin after birth:

At birth, prolactin secretion drops to nonpregnancy levels

• Every time infant nurses, prolactin levels spike

• This stimulates synthesis of milk for the next feeding

  • more stimulation, the more spikes in prolactin, up-regulating milk synthesize

• Without nursing, milk production stops in 1 week

• Only 5% to 10% women become pregnant while breast-feeding

  • bc breastfeeding down regulates ovarian cycle and GnRH production

  • makes breast feeding a natural means of spacing births

Milk Ejection

Need manual stimulation of areola to eject milk

• oxytocin gets released and causes smooth muscle contractions to help squeeze milk into duct

• Milk ejection is controlled by a neuroendocrine reflex

• Milk flows within 30 to 60 seconds after suckling begins

Breast Milk

• Supplies antibodies and colonizes intestine with beneficial bacteria

• Nursing woman can produce 1.5 L of milk per day

• Breast milk changes composition

  • Changes over the first 2 weeks

  • Varies from one time of day to another

  • Varies over 20 minute feeding

• At the end of a feeding there is less lactose and protein, but six times the fat

Meconium

green, bile-filled fecal material in newborn

• Colostrum and milk have a laxative effect that clears intestine of meconium

• this is why babies tend to have to defecate when breastfeeding

Why is cows milk not a good substitute for breast milk?

• Has 1/3 less lactose but 3x as much protein

• Harder to digest and more nitrogenous waste (causing diaper rash)

Contraception

any procedure or device intended to prevent pregnancy

Behavioral Methods of Contraception

• Abstinence

• Rhythm method (periodic abstinence)

  • timing intercourse to avoid intercourse during ovulation

• Withdrawal (coitus interruptus)

Barrier and Spermicidal Methods of Contraception

• Male and female condom

• diaphragm / sponge

  • putting something in vaginal canal to block the external os

• Spermicides: foams, creams, jellies

Hormonal Methods

Most hormonal methods prevent ovulation

• “The pill”

• “Morning after pills”

• RU-486

The Pill

an estrogen and progestin (form of progesterone) patch, injection, or vaginal ring

• Ovarian follicles do not mature bc FSH, LH are inhibited by the estrogen and progesterone

Morning After Pills

emergency contraceptive pills

• These pills have a high dose of estrogen and progestin, or progestin alone

• Inhibit ovulation, movement of sperm and egg, and implantation

• Induce menstruation if implantation has not occurred

RU-486

AKA “abortion pill”

• progesterone antagonist

• goal is to remove embryo from uterus

• Induces chemical abortion up to 2 months into pregnancy.

  • Two doses over two days

• Can be reversed with high dose of progesterone after first dose of RU-486.

• If second dose of RU-486 has been administered, reversal is not possible

Intrauterine Device (IUD)

Device that is left in place in the uterus for an extended period of time

• Irritates uterine lining and interferes with implantation

Surgical Sterilization

Clamping or cutting the genital ducts (uterine tubes or ductus deferens)