51. Role of Prostaglandins in obstetrics
Prostaglandins:
= group of active lipids called eicosanoids
- found in every tissue in humans
- powerful locally acting vasodilators and inhibit the aggregation of blood platelets
- also, they are involved in inflammation
- PG are synthesized in the walls of blood vessels
- -> inhibit clot formation
- -> and regulate smooth muscle contraction
- in parturition -> role in myometrial contractility, relaxation, and inflammation
- act on 8 different G – coupled receptors found in myometrium and cervix
- Arachidonic acid, released by Phospholipase A2
- with help of COX -> convert arachidonic acid to the unstable prostaglandin G2 and then to prostaglandin H2
- PgH2 is then converted to an active prostaglandin, which are = prostaglandins E2 (PGE2), F2α (PGF2α), and I2 (PGI2)
- 15-hydroxyprostaglandin dehydrogenase (PGDH) is an important enzyme which is needed for the Pg metabolism -> it is up-regulated during pregnancy in uterus and cervix to be able to rapidly inactivate Pg
- myometrial balance is kept by Pg synthesis vs. its metabolism
- = prostanoids can lead to myometrial relaxation at one stage of pregnancy and to myometrial contractions after parturition (labor) initiation
- Pg are also found in the amnion -> myometrial relaxation or contraction
- in later stage of pregnancy, their levels are increased and phospholipase A2 and PGHS-2 show greater activity
- the main role of Pg in amnion is the membrane rupture
- during labor, 3rd stage: levels of prostaglandins in amnionic fluid, maternal plasma, and maternal urine are increased -> contractions
- fetal membranes and placenta also produce prostaglandins (PGE2, PGF2α)
- highest elevation in amnion is after labor begins -> cervical dilation and exposure of decidual tissue
- the rise in cytokine and prostaglandin concentrations degrade the extracellular matrix-> weakening fetal membranes -> membrane rupture
- receptors for PGE2 and PGF2α are expressed in the uterus and cervix -> respond in exposure
- treatment with Pg in pregnant women -> abortion or labor at all gestational ages
- <-> prostaglandin H synthase type 2 (PGHS-2) inhibitors to pregnant women will delay spontaneous labor onset and sometimes arrest preterm labor
53.Elective surgical abortion – 1 st and 2nd trimester
- 1st trimester
=> Surgical evacuation is performed transvaginally through an appropriately dilated cervix
Surgical preparations:
- prior to surgery, cervical ripening (=dilation) is performed
- hygroscopic dilators, also called osmotic dilators, are devices that draw water from surrounding tissues and expand to gradually dilate the endocervical canal
- hygroscopic dilators are either devices derived from Laminaria algae or the device is Dilapan-S
- each type expands to an ultimate diameter three to four times that of its dry state
- Dilapan-S achieves this in 4 to 6 hours, which is faster than the 12 to 24 hours needed for laminaria
- instead of hygroscopic dilators, misoprostol is often used for cervical ripening → administered sublingually, buccally, or placed into the posterior vaginal fornix 3 to 4 hours prior to surgery
- Another effective cervical-ripening agent is the antiprogestin mifepristone, 200 mg given orally 24 to 48 hours before surgery
Vacuum Aspiration:
=> Also called suction dilation and curettage or suction curettage, vacuum aspiration is a transcervical approach to surgical abortion
- a rigid cannula is attached either to an electric-powered vacuum source or to a handheld 60-mL syringe for its vacuum source
- So there is either electric vacuum aspiration (EVA or manual vacuum aspiration (MVA)
- vacuum aspiration at minimum requires intravenously or orally administered sedatives or analgesics, and some add a paracervical or intracervical blockade with lidocaine
- If required, the cervix is further dilated with Hegar, Hank, or Pratt dilators until a suction cannula of the appropriate diameter can be inserted