Episode 87: Maternal-fetal monitoring with Stephanie Martin

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We learn about the basics of fetal monitoring in the critically ill pregnant woman and how to integrate them into our ICU workflows, with Stephanie Martin, MFM obstetrician and host of the Critical Care Obstetrics podcast and teacher at the Critical Care Obstretrics Academy.

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Takeaway lessons

1. A fetus is considered potentially viable at 23-24 weeks gestational age, with 22-23 weeks being occasionally viable in specific circumstances and highly specialized centers. “Potentially viable” does not mean guaranteed survival, as fetal mortality is still quite high. In other words, at 23 weeks and above, intervention to promote fetal survival make sense. Every additional day of gestation improves outcomes.
2. A conversation should occur preemptively between the mother, ICU, and obstetric teams to clarify what options will be considered—in some circumstances, early delivery (via C-section) is not desired due to the risk to the mother, and should not be assumed to be the contingency in all viable pregnancies. On the flip side, delivery of a non-viable fetus could still be appropriate for the mother’s health, such as in uterine infection or hemorrhage.
3. If a fetus will not be delivered early, there may be no role for fetal monitoring.
4. Fetal monitoring is therefore relevant at viable gestational ages. However, it is also more difficult for early pregnancies; the monitors can easily wander off a tiny fetus, and the strips are harder to interpret.
5. Fetal monitors essentially monitor 1. Fetal heartrate (via Doppler), and 2. Uterine contraction. Heartrate is monitored primarily to determine variability, i.e. how much the rate changes from its average baseline in response to stimulus, particularly uterine contraction (which causes fetal stress of sorts). Poor variability with markers like late decelerations can be a sign of fetal acidosis and ischemia, particularly to the brain, which can increase the risk of fetal demise or birth defects such as cerebral palsy. Prematurity creates particular vulnerability to this.
6. Maternal sedation leads to fetal sedation, which can make interpreting the heart rate more difficult.
7. Uterine contractions rarely turn into labor, but they provide a natural stress test to the fetus.
8. Much of the interpretation of “fetal distress” comes down to the context—for instance, maternal acidemia will always cause fetal acidemia, but in a rapidly reversible setting such as DKA, the best solution may simply be resuscitating the mother.
9. Fetal distress is often an early marker of shock and other systemic stress, as uterine perfusion is sacrificed fairly early by the body in favor of other organs. This often manifests as uterine contractions.
10. Any pregnant woman with a gravid uterus up to the umbilicus, or >20 weeks, who is critically ill, should not lie supine; the uterus will compress the great vessels and may cause shock. Elevate the head of the bed or tilt them laterally at all times. (During CPR, assign someone to manually displace the uterus to the left, as tilting the entire patient is challenging.)
11. There is relatively little role for ultrasound or other tools for fetal monitoring; the gold standard is fetal heart rate monitoring.
12. Paroxysms of vital sign changes (tachycardia, hypertension, etc) in a pregnant woman could be a subtle marker of contractions.
13. With regards to ionizing radiation, generally, do whatever test you would do in a non-pregnant woman. Birth defects are generally established by the end of the first trimester, so in a viable pregnancy, it should not be a concern at all. While appropriate attention should be paid to avoiding needless radiation, if an important diagnosis needs to be made, do the x-ray or CT scan (or even fluoroscopy, likely the highest risk).
14. In the post-partum patient, the longer it’s been since birth, the less likely a maternal illness is pregnancy-related. In the first week, assume it’s pregnancy related. In the first six weeks, consider it, especially hypertension complications. Cardiac problems (e.g. peripartum cardiomyopathy) can occur even later, especially as the diagnosis may be delayed. A common presentation is post-partum “asthma,” actually pulmonary edema, as the fluid bolus of delivery overloads a cardiomyopathic heart. The most hypercoagulable period in pregnancy is actually the first six weeks post-partum, so VTE is an important concern.