OB/GYN

First Trimester Bleeding

1.6% ED visits (overall)
?IUP: up to 50% SAb
+FHR +bleeding: 14% SAb (Juliano, Ann EM, 2008)

>50% (up to 2/3) of SAb lost due to chromosomal abnormalities (not preventable)

We don't need to give RhoGAM for first trimester bleeding.  Fetal blood volume 0.3cc, 1cc needed for alloimmunization. (Zipursky, Can Med Assoc J, 1967)






Placental Exchange
Size

Most drugs with MW < 500 Da cross the placenta, and most drugs with MW > 1000 Da do not cross the placenta (ex. heparin, protamine, insulin). Neither succinylcholine (highly ionized) or non-depolarizing NMBDs (high molecular weights) cross the placenta.
Charge

Non-ionized drugs tend to cross the placenta more easily than ionized drugs, however the fetus usually has a lower pH than the mother, leading to “ion trapping.”

Protein Binding

Traditionally it was taught that protein-bound drugs did not cross the placenta, however as these medications exist in equilibrium with non-bound versions, it appears that this is not true [Pacifici GM and Nottoli R. Clin Phamacokin 28: 235, 1995]
Lipophilicity

While liphophilicity is generally advantageous with regards to placental transfer, extreme lipophilicity (ex. sufentanil) may impede transfer as highly lipophilic substances can accumulate in the placenta
Specific Anesthetic Agents

All inhalational agents and most intravenous agents used by anesthesiologists will cross the placenta – inhalational agents cause very little fetal depression if used at < 1 MAC and delivery occurs within 10 mins of induction. Thiopental, propofol, benzodiazepines, and ketamine all cross the placenta, although only benzodiazepines are noted to produce significant fetal effects. Opiates all cross the placenta to some extent (amount is variable) – from a respiratory standpoint, newborns are most sensitive to maternal morphine.Fentanyl appears to be safe if given at < 1 ucg/kg. Epidural opiates produce minimal effects. Ephedrine, B-blockers, vasodilators, metoclopramide, and atropine cross the placenta, although glycopyrrolate (which also does not pass the blood-brain barrier) does not

Summary of Placental Transfer of Anesthetic Drugs


DRUGS WHICH DO NOT CROSS THE PLACENTA
All paralytics
Glycopyrrolate
Insulin
Heparin

DRUGS WHICH CROSS THE PLACENTA Potentially Dangerous
Opiates (morphine, fentanyl if > 1 ucg/kg)
Benzodiazepines
Ephedrine (increased metabolism)
Local anesthetics
Atropine
B-blockers

Safe
Propofol
Thiopental
Ketamine
Fentanyl at < 1 ucg/kg
Epidural opiates (fentanyl, sufentanil)


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15-25% of pregnancies, 50% miscarriage  133k v. 2 Nov 23, 2011, 12:25 PM Kit Tainter
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