Paramedic listening for fetal heart tones with a digital stethoscope in an ambulance

Why EMS Should Listen for a Second Heartbeat

November 2, 2026

As a medic, you probably weren’t taught to listen for fetal heart tones. If you were, it was likely only as part of an OB-specific exam. For trauma and most medical calls, we generally treat mom, because her circulation is the baby’s circulation. Keeping her alive and well perfused is usually the best thing we can do for both of them, and treating suspected fetal distress in the field typically isn’t within our scope.

Still, the baby may have something to tell us. In my experience, ground crews don’t often listen for fetal heart tones. Many flight programs expect crews to try on every pregnant patient, but the reason behind it doesn’t always get much attention. That’s a missed opportunity, because the baby may be one of the earlier warning signs we have for mom.

Mom May Hide Shock Well

Pregnancy changes the math on shock. Mom’s blood volume goes up significantly, and she can compensate for a surprising amount of blood loss. NAEMSP’s 2025 trauma compendium notes that a pregnant patient may lose up to 1.5 L of blood before her vitals change.

So who might notice first? Possibly the baby. When mom starts protecting her own core, blood flow to the uterus can drop. NAEMSP and ACEP both describe an abnormal fetal heart rate as potentially the earliest sign that mom is in trouble, sometimes before her heart rate, BP or skin signs change.

Seen that way, the baby can act as a window into mom’s perfusion. We’re not listening to treat the fetus. We’re listening for another clue about how mom is really doing.

What’s Normal

Normal fetal heart rate: 110–160 bpm
Tachycardia: above 160
Bradycardia: below 110

When a fetus is short on oxygen, the heart rate often climbs first and may then fall. StatPearls advises treating any sustained fetal heart rate under 120 after trauma as fetal distress. For us, that’s a reason to think about maternal blood loss, even if mom’s vitals look okay.

Estimate Gestation First

Before you look for heart tones, it helps to know roughly how far along she is. If she doesn’t know, or can’t tell you, fundal height can get you in the ballpark. The fundus is the top of the uterus.

Just above the pubic bone: about 12 weeks
Halfway between the pubic bone and umbilicus: about 16 weeks
At the umbilicus: about 20 weeks
Above the umbilicus: a rough field estimate is about 1 week for every centimeter above the umbilicus. 4 cm above would be around 24 weeks.

The more accurate version is measuring from the pubic bone to the fundus with a tape. After 20 weeks, the number of centimeters roughly equals the number of weeks. Using the umbilicus as your starting point may be the quicker option in the field. Neither method is precise: obesity, twins, fibroids, a full bladder and the baby’s position can all throw it off.

Why it matters: around the umbilicus (about 20 weeks) you have a reasonable chance of hearing tones with a stethoscope. Below that you’ll likely need a Doppler, and not hearing anything may not tell you much.

Where and When to Listen

Your best chance is somewhere quiet. That could be on scene, in the house, in a parked ambulance, in the bay, or in the aircraft before startup or after shutdown. In a moving rig or a running aircraft, hearing fetal heart tones is unlikely.

If you can, get a baseline early, and consider listening again after a significant change: a drop in BP, more bleeding, a long extrication, or before handoff.

The Challenge With a Standard Stethoscope

A regular acoustic stethoscope isn’t built for this. Midwives describe fetal heart tones as much harder to hear through a regular stethoscope than through a Pinard fetoscope. Guidelines like NICE’s recommend a Pinard or a Doppler rather than a standard scope.

There’s also a common trap: hearing mom’s pulse and counting it as the baby’s. NICE recommends feeling mom’s pulse while you listen so you can tell the two apart. If the “fetal” rate matches mom’s radial, you may be counting mom.

Where a Digital Stethoscope May Help

This is where an amplified digital stethoscope like the Littmann Eko 500 or Eko CORE could make a difference. Studies outside obstetrics show amplified stethoscopes picking up faint, low-frequency heart sounds better than standard scopes, and they may help in noisy settings and for clinicians with hearing loss. Bench testing shows the Eko CORE’s cardiac mode boosts the low frequencies. Researchers have also recorded usable fetal heart sounds with electronic stethoscopes late in pregnancy.

To be fair, I couldn’t find a study testing an Eko on fetal heart tones against a Doppler. But if a standard scope is what you carry, a digital scope set to cardiac or low-frequency mode may give you a better shot at hearing that second heartbeat.

If you carry one, keep it ready: a Power Blocker for the Eko CORE keeps the battery from draining in your pocket, and a belt holster for the Eko 500 keeps it on you instead of buried in a bag when you need a quiet minute to listen.

Field Tips

Estimate gestation by fundal height first.
Listen over the baby’s back if you can tell where it is, often lower on the abdomen.
Feel mom’s radial pulse while you count.
Try the bell, or cardiac or low-frequency mode on a digital scope.
Count for a full minute if time allows.
If you can’t hear tones, it may be worth treating that as a finding rather than reassurance. Pass it along at handoff.

What It Doesn’t Change

A normal fetal heart rate in the field doesn’t rule out a placental abruption. After trauma, mom still needs hours of continuous fetal monitoring at the hospital, even if everything looked good. An abnormal rate generally doesn’t change who you’re treating. It may change how closely you look at mom: oxygen, positioning, fluids or blood per your protocols, and choosing the right destination.

The Bottom Line

We generally keep mom alive so mom can keep baby alive. But the baby may be able to tell us when mom is in more trouble than she looks. If you have a quiet minute, it might be worth finding that second heartbeat and letting it sharpen your assessment of the patient you’re treating.

Follow your local protocols and medical direction.

Protect Your Eko

If you’re counting on a digital scope to pick up faint sounds like fetal heart tones, protect it, track it, and keep it within reach. These accessories are designed and tested for the Littmann Eko 500 and Eko CORE:

Protective Cover for the Eko CORE

Littmann Eko CORE Power Blocker

Protection Cover for the Eko 500

Eko 500 Bezel Cover

Eko 500 Belt Holster

AirTag Holder for Littmann Stethoscopes