Pregnancy Loss and Parturition

Reading

• Chapter 14
• Handout 7: Pregnancy and Parturition
• Diagrams not found in text (see powerpoint file or powerpoint handout)

Prenatal loss

• Optimal condition fertilization approaches 100%
• Losses
  • 2/3 loss during embryonic development
    • blastocyst hatching, blastocyst formation, failure to prevent CL regression, delayed development
  • 1/3 loss during fetal stage
    • crowding, placental insufficiencies
• Increased prenatal losses
  • nutritional stress
    • energy shortages
    • mineral imbalances
    • vitamin deficiencies
  • diseases of the reproductive tract
  • endocrine imbalances
  • age of gametes prior to fertilization
    • better to inseminate early

Fetal control of parturition

• fetus controls time of parturition due to stress response
  • lack of space
  • lack of gas exchange
  • lack of nutrients
• Hormonal changes at the end of gestation (figure 14-10 in text)
  • fetal pituitary - hypothalamus axis essential
    • increased stress from fetal nutrional demands and placental insufficiency
    • hypothalamus releases CRH
    • anterior pituitary in turn releases ACTH
  • fetal adrenal gland
    • in response to ACTH releases cortisol (corticosteroids)
      • effects of cortisol on fetus
        • Lung produces surfactants
        • liver increases storage of glycogen
        • thyroid increases metabolism
      • effects of cortisol on placentome
        • shift from progesterone to estradiol production
          • progesterone decreases
          • estrogen increases
        • PGF increases
  • Placentome hormones
    • estradiol
      • increase gap junc tions in myometrium
        • leads to better coordination and communication among muscle cells in the myometrium
        • begin to get coordinated contrations toward the cervix
      • increase in uterine oxytocin receptors
      • primes cervix to respond to relaxin
      • stimulates ovary to secrete relaxin and oxytocin
      • acts with PGF to trigger CL regression
    • PGF
      • regression of CL
      • synthesis and release of oxytocin and relaxin from ovary (in some species relaxin from placenta)
      • stimulates most of the contrations in the uterus
    • progesterone
      • when present suppresses contrations in the uterus
      • shift from progesterone to estrogen production leads to its decrease from the placentome
      • PGF stimulates luteolysis so progesterone from CL decreases
      • release from "progesterone block"
  • relaxin
    • comes from ovary or placenta
    • synthesis stimulated by PGF
    • stimulates softening of the cervical connective tissue to cause dilation
    • promotes elasticity of the pelvic ligaments
  • oxytocin
    • stimulates final contractions of uterus but only once fetal head enters cervix

Orientation of fetus

• fetus must reorient prior to parturition
  • initially on back
  • reorient so feet and head will exit first
  • breech
    • rear or fetus comes first
• orientation not important in pig
• abnormal orientation results in dystocia

Stages of labor

• preparative (2 to 12 hours)
  • myometrial contractions
  • uterine pressure
  • adominal discomfort
  • cer vical dilation
• expulsion of fetus (30 min to 180 min)
  • strong uterine contractions
  • rupture of the allantochorion
  • appearence of amnion
  • maternal recumbency and straining
  • not only uterine but adominal contractions as well
  • rupture of the amnion and delivery
• expulsion of placenta (1 hr to 12 hr)
  • uterine contractions decrease but continue
  • chorionic villi loosen
  • expulsion of placenta
  • delayed in ruminants due to presence of cotelydons separating independently
  • suckling induces oxytocin release which triggers further uterine contractions

Dystocia (difficult birth) causes

• abnormal presentations
• excessive fetal size
• multiple births (twins)
  • twins presented at same time
  • one is usually blocking the other
  • uterus becomes fatigued

Perinatal fetal changes

• cardiovascular
  • ductus arteriosis
  • foramen ovale
  • ductus venosus
• thermoregulatory
  • must regulate own temperature
  • increase metabolism (thyroid activity)
  • brown fat - metabolism of produces principally heat
• energy metabolism
  • until suckling relies on own stores of glycogen
• immune status
  • has no antibodies
  • get passive immunity from mother (gut permeable to antibodies in colostrum)
    • only first 6-12 hours after birth
  • in rabbit, rat, man some is absorbed through placenta prior to birth

Uterine involution and return to estrus

• Uterine Involution - initial 7 days but weeks to fully complete
  • myometrium
    • must return to pre-pregnancy state
    • shrinkage and atrophy
  • lumen
    • elimination of bacteria
  • endometrium
    • repair
    • restore glandular activity
• Estrous cycles - between 30 to 70 days postpartum get first estrus in cattle
  • hypothalamus
    • GnRH pulses must start again after long time with progesterone negative feedback
  • anterior pituitary
    • response to GnRH requires synthesis of LH and FSH
  • ovaries need to respond to FSH and LH to produce follicles
  • follicles must produce steroids
    • first ovulation silent estrus (since no progesterone)
    • then get normal cycles
    • estrogen triggers estrus behavior and ovulation
  • fertility increases with # of estrus cycles
    • first - 35% pregnancy rate
    • second - 50%
    • third - 73%
    • fourth - 72%
  • lactational anestrus
  • special postpartum estrus
    • mare
      • foal heat, 6 - 13 days postpartum
      • fertility depends on body condition of female
    • sow
      • anovulatory estrus 3 - 5 days post farrowing
      • weaning induces estrus 3 - 5 days latter

Retained placenta

• most common in cattle (5 - 15%)
  • not seen in mares, sows or ewes
• cause
  • normally get lack of blood flow to chorionic villi and this causes them to regress
  • high incidence in premature or early delivery (270 to 275 days)
  • high milk producers
  • twins
  • difficult births with dystocia
  • artificial induction of parturition
  • nutritional deficiencies
    • vitamin A
    • selenium
• definition
  • if not expelled within 24 hr it may be retained for 5 - 6 days
• treatment
  • manual removal not recommended
  • daily antibiotics
  • large single antibiotic bolus
  • oxytocin or PGF

Induced parturition

• Dexamethazone (potent synthetic cortisol)
  • all species
• PGF
  • pig, cattle, sheep
• Oxytocin
  • human, horse

Species Specific Procedures for Induction of Parturition

• Cow
  • Restrictions - Do not induce before day 269 of gestation
  • Methods
    • Dexamethasone - 48 hrs to parturition
    • Dex + PGF - 35±2 hrs to parturition
• Ewe
  • Methods
    • Dexamethasone - 24 to 72 hrs
    • PGF but multiple injections required
• Sow
  • Restrictions - Must be at least 111 days into pregnancy
  • Methods
    • PGF - 29 - 48 hrs
    • PGF followed by Oxytocin 24 hrs latter - farrow 8AM - 5PM
    • Oxytocin can be given to decrease stillborns in large liters or after a long parturition

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