# OB Question



## DragonClaw (Jun 12, 2020)

Okay so I'm forgetting a word.

We were in the OB ED and took a lady to the level one trauma center cause she had pre-eclampsia and twins and other high risk stuff.

On the way out, one nurse points out to another nurse some vitals. 

They kept using this term.  Like "unusual variable" or something?

I forget the word.

I asked them what it meant, they said it either meant the cord was being moved or compressed.

I asked if it was possibly a sign of nuchal cord or a cardiac event. They said yes.

Any idea of what the actual word is? How do they get this data? They were pretty busy because the bag was already presenting and stuff at like 19 weeks.

I guess it's pretty serious cause they said it off happens once and sorts itself out, it's whatever.  But this was 2 times in 10 minutes and it wasn't really correcting. They were getting drs on the phone and stuff.


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## Peak (Jun 12, 2020)

DragonClaw said:


> Okay so I'm forgetting a word.
> 
> We were in the OB ED and took a lady to the level one trauma center cause she had pre-eclampsia and twins and other high risk stuff.
> 
> ...



I assume they are interpreting cardiotocography. Other terms you might have heard were FHM or toco.

We expect an amount of variability and decelerations (frequently called ‘decels’). Contractions will normally cause an amount of decelerations as the squeezing of the head causes vagal stimulation in the fetus. This should recover quickly.

Persistent fetal bradycardia, frequent decels not correlating to contractions, or decels that take too long to recover is concerning for acidosis or hypoxia (which is concerning for fetal distress). Fixed heart rates without variability are concerning for a fetal arrhythmia.

I am not trained in reading CTG strips and have a limited understanding as I just care for baby once they are delivered. ‘Normal’ heart rate is like 110 to 160, but really unless there is a contraction I expect a fetal heart rate of 140 to 160 sitting mostly 150 to 160. Drops below 110 and especially 100 are very concerning as they are bradycardia in the neonate. Decels that do not recover quickly are also concerning as the kid isn’t requiring quickly enough. There are a lot of graphs out there but once viability is reached we expect resting heart rate to slowly decrease until term.

A brief review of fetal circulation is that there is very low systemic vascular resistance and very high pulmonary vascular resistance. Blood bypasses ordinary circulation by a number of means. The Ductus Arteriosis (called a PDA or patent ductus arteriosis when they are born and it doesn’t close spontaneously) bypasses the lungs by shunting blood from the pulmonary artery to the aorta. The foramen ovale (PFO or patent foramen ovale when born) is a physiologically (as a fetus) normal hole in the atrial septum (as opposed to abnormal/pathological ASD or atrial septal defects) shunts blood from the right atria into the left. These together create the fetal right to left shunt. The ductus venosus rounds our normal fetal shunts and connects the flow from the umbilical vein in the portal vein into the vena cava which to a degree spares perfusion to the liver and into the rest of the fetal circulation.

Compared to neonatal circulation the fetus has a lower pH and oxygen saturation. The relatively small demand means that unless the fetus is distressed there shouldn’t be a lot of demand or variability.

Unfortunately 19 weeks is not viable, although the actual gestation can vary as few moms know the actual date of conception and ultrasound dating has a degree of variability. Dating based on last menstration is also questionable as there is a time period of which the uterine wall is able to be attached to, and some women can have some normal bleeding or spotting that they mistake for menstration up to two months in their pregnancy. The earliest survival is 21.5.


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