Endocrinology pregnancy parturition Flashcards
List the changes to key systems during pregnancy
- Cardiovascular: increased RR, lower BP, higher CO (HR and SV)
- Respiratory: increased RR, reduced tidal volume (compression of thoracic cavity by uterus)
- Renal: increased total body water, circulating blood volume, GFR, and RBF
- Gastrointestinal: decreased gastric motility
- Coagulation: reduced platelets, increased clotting factors (pro-/hypercoagulant state)
- Central nervous system: changes in cognitive function, mood, memory
Describe the production of hormones during pregnancy
- Luteal progesterone levels maintained after implantation
- Corpus luteum is the key structure of hormone secretion: oestrogen and progesterone
- maintained by Human Chorionic Gonadotrophin (HCG) produced by the early trophoblast ^[trophoblast will eventually become placenta]
- Placental production of steroid hormones starts from 8 weeks
- Placental production of steroid hormones (progesterone, estrogen, human placental lactogen) reflects placental growth (increases as a function of placental growth because it increases throughout gestation)
Describe the feto-placental unit and production of hormones
- Oestrogen production requires feto-placental interaction (mother plus placenta plus fetus)
- Maternal cholesterol converted to pregnolone by placenta, converted by fetal adrenal gland to DHEA-sulfate
- Convertd by fetal liver enzymes to 16-alpha-DHAS, aromatized by the placenta to estriol
Describe the regulation of uterine contractility
- Massive growth in myometrial tissue (hypertrophy & hyperplasia)
- Muscle fibres are stretched, but don’t contract (minimal)
- Uterus maintains regular activity from about 12 weeks (Braxton-Hicks contractions appear 1 month before labour, sporadic contraction and relaxation of uterine muscle for 1-2 minutes)
- oestrogen increases relative to progesterone resulting in increased prostaglandin production at uterus, activation of inflammatory pathways at myometrium, causing increased intracellular calcium concentration of uterine smooth muscle, increasing contractility, as well as thinning and dilation of cervix early in labour
- At labor onset, contractions become more frequent, regular, and stronger, and show ‘fundal dominance’ (expulsive)
- Birth achieved through a combination of maternal effort and uterine contractions
- three stages:
- stage 1: from onset of delivery to 10 cm cervical dilation
- stage 2: from 10 cm dilation to delivery
- stage 3: from delivery of baby to delivery of placenta
- oxytocin likely mediates a role in stage 2-3
- three stages:
- Changing influences of progesterone & estrogen (oestradiol AND oestriol)
- Local production of active prostaglandins (PGF2 alpha & PGE2)
- Other local cytokine pathways maintain the inflammatory cascade
- Oxytocin production by the posterior pituitary – likely most important in second and third stages of labour
PG pathway:
- phospholipids containing arachidonic acid are converted to free amino acids by phospholipase (Free amino acids can also form phospholipids)
- Free acids are converted to several end-products depending on the enzyme:
- epoxy-acids, by monooxygenase
- prostaglandins, by COX-1 and COX-2
- HETEs and leukotrienes, by lipooxygenases
Briefly describe changes to cervix during pregnancy
- The cervix is a dense, collagenous structure
- Closed and a mechanical barrier during pregnancy
- Must soften and allow for dilation at parturition (up to 10 cm dilation)
- Reforms (remodels) completely after birth, all under local hormonal control
Discuss stats related to labour and birth in Australia
- 2009: 299,220 babies born in Australia
- Average age of birthing women: 30
- 56.1% experienced spontaneous labor, 25.1% had labor induced
- 31.5% born by cesarean section, 10.4% assisted vaginal deliveries
Describe the onset of labour and its determinants
The Onset of Labour
- 90% of all human babies born at term (37-42 weeks)
- 7-8% pre-term, 2-3% post-dates
- Mode of age at birth is 40 weeks from LMP
Evidence for Fetal Control
- Observations in anencephalic fetuses = evidence for foetus influence
- Babies with congenital adrenal hyperplasia born early = evidence for foetus influence
- Sheep eating Veratrum californicum give birth to postmature lambs with no pituitary
- Fetal hypohysectomy prevents parturition in sheep
- Corticosteroids induce labor in fetal sheep
- Maternal CRH levels may determine the time of birth in human pregnancy = evidence of mother’s influence
Note: determination of time of labour may also be influenced by placenta
Describe the elements of postpartum recovery and puerperal hormonal influences
- Characterized by anovulation & amenorrhea, lactation, uterine involution (connective tissue remodelling under local control), physical & emotional recovery, postnatal depression
Puerperal Hormonal Influences
- Hypogonadotrophic state with low estrogen levels
- Prolactin stimulates lactation
- Oxytocin involved in suckling and ‘let-down’ reflex
- Connective tissue remodeling under local control (collagenase production is triggered by withdrawal of progesterone and oestrogen)
- Uterine involution takes about six weeks
- Menstruation resumes at 6-9 months if breastfeeding
Describe the physiology of lactation
- ## Prolactin & oxytocin have important roles in breastfeeding and mother-infant attachment
- crying signals the cortical regions
- signalling the hypothalamus
- stimulating the production of prolactin
- note PIH or dopamine
- prolactin encourages milk secretion from the mammary glands
- note also the action of oxytocin, released from the posterior pituitary
- stimulates smooth muscle contraction, assisting in the delivery of milk
- positive feedback from suckling baby enhances the ‘let down’ reflex, inhibiting PIH
