Pregnancy is the presence of a developing offspring in the uterus. It results from the union of an egg and a sperm cell – an event called fertilization.

-To reach the egg cell, sperm cells must travel upward through the uterus and uterine tubes.

-Prostaglandins in the semen stimulate lashing of sperm tails and muscular contractions of the uterus and uterine tubes, which help sperm cells move.

-High estrogen concentrations during the first part of the menstrual cycle stimulate the uterus and cervix to secrete a thin, watery fluid that promotes sperm transport and survival.

-During the latter part of the cycle, when progesterone concentration is high, the female reproductive tract secretes a viscous fluid that hampers sperm transport and survival.

-Sperm cells reach the upper uterine within an hour following sexual intercourse.

-Many sperm cells may reach the egg cell, but only one actually fertilizes it.

-The sperm cell that reaches the egg invades the follicular cells that adhere to the egg cell’s surface (corona radiata) and binds to the zona pullucida surrounding the egg cell membrane.

-The acrosome of the sperm cell releases an enzyme (hyaluronidase) that aids penetration.

-Union of the egg cell and sperm cell triggers lysosome-like vesicles just beneath the egg cell membrane to release enzymes that harden the zona pullucida around the fertilized egg cell, reducing the chance that other sperm cells will penetrate.

- Once the sperm cell enters the egg cell’s cytoplasm, the nucleus in the sperm cell’s head swells.

- The egg cell then divides unequally to form a large cell and a polar body (later expelled).

- The nuclei of the egg and sperm cell unite, nuclear membranes disassemble, and their chromosomes mingle, completing fertilization.

- This cell, called a zygote, is the first cell of the future offspring.

-Cells undergo mitosis, giving rise to smaller and smaller cells. This process is called cleavage.

-The developing offspring moves down the uterine tube to the uterus, where it implants in the endometrium.

-The offspring is called and embryo from the second through eighth week of development. Thereafter, it is a fetus.

-Eventually, embryonic and maternal cells form a placenta, which attaches the embryo to the uterine wall and exchanges nutrients, gases, and wastes between maternal blood and the blood of the embryo.

-The placenta also secretes hormones.

- Following implantation, embryonic cells begin to secrete human chorionic gonadotropin.

- Human chorionic gonadotropin maintains the corpus luteum, which continues to secrete estrogen and progesterone.

- The developing placenta secretes large quantities of estrogen and progesterone.

- Placental estrogen and progesterone:

- Stimulate the uterine lining to continue development

- Maintain uterine lining

- Inhibit the anterior pituitary’s secretion of FSH and LH

- Stimulate development of mammary glands

- Inhibit uterine contractions

- Enlarge the reproductive organs

- Relaxin from the corpus luteum inhibits uterine contractions and relaxes the pelvic ligaments.

- The placenta secretes placental lactogen that stimulates breast development.

- Aldosterone from the adrenal cortex promotes sodium reabsorption, leading to fluid retention.

- Parathyroid hormone from the parathyroid glands help maintain a high concentration of maternal blood calcium.

-The embryonic stage extends from the end of the second week through the eighth week of development.

-During this stage, the placenta and main internal and external body structures develop.

-The cells of the inner cell mass organize into primary germ layers.

-The embryonic disk becomes cylindrical and attaches to the developing placenta.

- The placental membrane consists of the epithelium of the chorionic villi and the epithelium of the capillaries inside the villi.

- Oxygen and nutrients diffuses from maternal blood across the placental membrane and into fetal blood.

- Carbon dioxide and other wastes diffuse from fetal blood across the placental membrane into maternal blood.

-A fluid filled amnion develops around the embryo.

-The umbilical cord forms as the amnion envelops the tissues attached to the underside of the embryo.

-The yolk sac forms on the underside of the embryonic disk.

-The allantois extends from the yolk sac into the connecting stalk.

-By the beginning of the eighth week, the embryo is recognizable as a human.

8 weeks- Head nearly as large as body; all major

brain regions present.- Liver disproportionately large- Limbs present; ossification just begun; - Weak, spontaneous muscle contractions

occur- Cardiovascular system fully functional- All body systems present in at least

rudimentary form- Approximate crown-to-rump length:

22mm

8 Weeks

9-12 Weeks-Head still dominant, but body elongating;

-brain continues to enlarge; -shows its general structural features; -cervical and lumbar enlargements apparent in spinal cord;

- retina of eye is present-Skin epidermis and dermis is obvious;-Nails seen on digits-Facial features present in crude form

9-12 Weeks cont…-Liver prominent and bile being secreted-Palate is fusing-Most glands of endodermal origin are developed

-Walls of hollow visceral organs gaining smooth muscle

-Blood formed in bone marrow-Notochord degenerating and ossification accelerating; limbs nicely molded

-Sex readily detected-Approximate crown-to-rump length at the end of interval: 36mm

13-16 Weeks-Cerebellum becoming prominent-Neuroglia beginning to differentiate-General sensory organs differentiated-Eyes and ears assume characteristic position and shape

-Blinking of eyes and sucking motions of lips occur

-Face looks human and body beginning to outgrow head

-Hard palate fused

13-16 Weeks-Glands developed in GI tract-Meconium (fetal feces) is collecting-Elastic fibers apparent in lung-Kidneys obtain typical structure-Most bones now distinct and joint cavities apparent

-Quickening occurs (mother feels spontaneous muscular activity of fetus)

-Approximate crown-to-rump length at the end of interval: 140mm

17-20 Weeks-Eyelashes and eyebrows present-Vernix caseosa (fatty secretions of sebaceous glands) cover body

-Lanugo (silk-like hair) covers skin-Fetal position (anterior flexion) assumed due to space restriction

-Limbs achieve final proportions-Approximate crown-to-rump length at the end of interval: 190mm

21-30 Weeks- Substantial increase in weight- May survive if born prematurely at 27-28

weeks; but, hypothalamic temperature regulation and lung production of surfactant are immature

- Myelination of cord begins- Eyes are open- Skin is wrinkled and red- Tooth enamel is forming on deciduous

teeth in gums

21-30 Weeks-Body is lean and well proportioned-Mesenteric attachements completed-Pulmonary branching is two-thirds complete

-Blood formation in bone marrow increasing

-Blood formation in liver is decreasing-Distal limb bones beginning to ossify-Approximate crown-to-rump length at the end of interval: 280mm

30-40 Weeks

- Skin whitish pink

- Fingernails and toenails present

- Fat laid down in subcutaneous tissue

- Testes in scrotum (in males)

- Approximate crown-to-rump length at the end of interval: 350-360mm

Anatomical Changes

-Maternal reproductive organs and breast become increasingly vascularized; breast enlarge.

-The uterus eventually occupies nearly the entire abdominal cavity.

-Abdominal organs are pushed superiorly and encroach on the thoracic cavity, causing the ribs to flare.

-The increased abdominal mass changes the woman’s center of gravity; lordosis and backache are common.

-A waddling gate occurs as pelvic ligaments are loosed by placental relaxin.

-A typical weight gain during pregnancy in a woman of normal weight is 29 pounds.

- Human placental lactogen has anabolic effects and promotes glucose sparing in the mother.

- Human chorionic thyrotropin results in maternal hypermetabolism.

-Many women suffer morning sickness, heartburn, and constipation.

-The kidneys produce more urine, and pressure on the bladder may cause frequency, urgency, and stress incontinence.

-Vital capacity and respiratory rate increases, but residual volume decreases.

-Dyspenea (shortness of breath) is common.-Total body water and blood volume increases dramatically.

-Heart rate and blood pressure rise, resulting in enhancement of cardiac output of 20% to 40% in the mother.

* Definitions

* Parturition - the process of giving birth

* Braxton-Hicks contractions

* “false labor”

* rhythmic and milder than true contractions

* Primigravida – first pregnancy

* Multigravida – 2 or more pregnancies

Initiation of Labor-When estrogen levels are sufficiently high, they induce oxytocin receptors on the myometrial cells and inhibit progesterone’s quieting effect on the uterine muscles.

-Fetal cells produce oxytocin, which stimulates prostaglandin production by the placenta. Both hormones stimulate contractions of the uterine muscles.

-Increasing stress activates the hypothalamus, causing oxytocin release from the anterior pituitary.

-This sets up a positive feedback loop resulting in labor.

Dilation Stage

-The dilation stage is from the onset of rhythmic, strong contractions until the cervix is fully dilated (10cm).

-The initial contractions are 15-30 minutes apart and last for 10-30 seconds.

-As labor continues, contractions become more vigorous and more rapid.

-As the infants head is forced up against the cervix, it begins to soften, becomes thinner (effaces), and dilates.

-Eventually the amnion ruptures (water breaks).

-The head of the fetus rotates as it descends through the pelvic outlet so that the greatest dimension of its head is in the anteroposterior line, which allows it to navigate the narrow dimensions of the pelvic outlet.

Effacement

-From full dilatation (begin pushing) to delivery of baby

-normal position – vertex (head down); 95% of all births

-engagement of head measured by “stations” 1. -5 to +5 2. 0 is engaged in the birth canal

- When the largest dimension of the baby’s head is distending the vulva, called crowning, an episiotomy may be performed to reduce tissue tearing.

-normal progression to delivery 1. head and upper shoulders, lower shoulder (takes the most time), rest of the body exits rapidly, umbilical cord is clamped 2. delivery is aided by contraction of abdominal muscles and diaphragm of the mother 3. takes 20 minutes to 2 hours

Vertex presentation: normal delivery presentation; allows the baby to be suctioned free of mucus and to breath even before it has completely exited from the birth canal

Breech and other nonvertex presentations: buttock first; delivery is much more difficult; often requiring the use of forceps

Transverse (shoulder):

- fetus is perpendicular to the birth canal

- requires manipulation or C-section

Face/brow:

- head enters the birth canal in a way that sutures of the fetal skull can’t overlap

- may prolong labor and cause severe facial edema

- increased fetal mortality if labor is prolonged

If the woman has a deformed or android (malelike) pelvis, labor may be prolonged and difficult.

This condition is called dystocia (last longer than 20 hours).

Besides causing extreme maternal fatigue, another possible consequence is fetal brain damage and decreases viability of the infant.

1. Separation of the placenta causing fetal asphyxia

2. Compression of the umbilical cord

3. Rupture of membranes increased risk of infection > 24 hours

A cesarean section is performed in many such instances.

-Delivery of the placenta and fetal membranes is accomplished within 15 minutes after birth.

-Important that all placental fragments be removed to prevent continued uterine bleeding after birth (postpartum bleeding).

-Since absence of one umbilical artery is often associated with other cardiovascular disorders in the infant, the number of blood vessels in the severed umbilical cord is counted.