The reason it is harder for you
Anterior placenta and hearing a heartbeat at home
If your placenta is at the front, there is a thick, blood filled organ between the phone and your baby. Everything you have read about how easy this is was written by somebody without one.
The third recording in the tool is real audio with no rhythm in it. Worth hearing an honest refusal before you need one.
Firstsong is not a medical device, not a doppler and it does not use ultrasound. Hearing nothing means nothing, and hearing something means nothing either. If you notice fewer movements than usual, call your midwife or maternity unit now. An anterior placenta is not a reason to wait.
What an anterior placenta actually is
The placenta attaches somewhere on the inside wall of the uterus. Anterior means the front wall, nearest your skin. Posterior means the back wall, nearest your spine. Neither is a fault or a complication. It is closer to a coin landing one way up rather than the other.
Most people are told about it in passing at the 20 week scan and never think about it again, until they try to listen to their own belly and nothing sounds like it does in the videos. So this page is about the one ordinary consequence it has for anybody listening at home.
Why it makes your belly quieter
A heart sound is a pressure wave, and pressure waves lose energy in everything they cross. Getting from your baby to a phone already means amniotic fluid, the uterine wall, your abdominal wall and your own tissue. An anterior placenta adds several centimetres of dense, highly vascular tissue to that path.
It does two things at once, and the second is the part people miss. It absorbs and scatters what comes from the baby, so less arrives. And it is itself noisy, because a large volume of your blood moves through it continuously, producing a low whoosh at your rate, in the same band heart sounds live in. Signal down and noise up, from one cause.
The engine has a floor and it is measurable. Below a signal to noise ratio of about minus 10 decibels, detection on the research data does not degrade gracefully. It goes to zero. That is the physics, and it is why an app that always shows you something is telling you about itself rather than your belly.
The numbers we have, and the one we do not
The middle number matters more to you than the headline. Even on research sensors, about one recording in six had nothing usable in it. A phone is not research equipment and your living room is not a recording session, so starting from a harder position means expecting a harder time.
What actually helps
- Go lower and further to the side than you think. None of this beats the physics, it just moves the odds. The instinct is the top of the bump, which is often where an anterior placenta is thickest. Try low, just above the pubic bone, out towards one hip.
- Work in a genuinely quiet room. Not quiet like a house in the evening. Quiet like no television next door, no fan, nobody talking.
- Use wired headphones. Best isolation and no lag. Bluetooth adds a couple of hundred milliseconds, which changes no rate but puts what you hear out of step with what is happening.
- Stay still longer than feels reasonable. Your breathing and any shift of your hand are far louder than a fetal heart. Rest the phone rather than hold it and give it a full minute. Most people give up at fifteen seconds.
- Do not press harder. Pressing shortens nothing that matters and adds contact noise. Firm steady contact beats pressure.
- Try again later rather than longer. The baby will be somewhere else in two hours, and position is the one variable that fixes itself for free.
Hear what a refusal sounds like
Before you spend an evening wondering whether you are doing it wrong, listen to the third clip in the tool. Real audio with no rhythm in it, and the engine says so instead of printing a number. That verdict is better met here than at eleven at night.
Runs in your browser. Nothing uploaded, no account, no cookie.
What it does not mean
- Not a sign that anything is wrong. A microphone failing to pick up a sound through several centimetres of tissue is a statement about acoustics, not about your baby.
- Not something you did badly. Placental position is not caused by anything you did and you cannot change it by lying differently.
- Not a broken app. One that finds a heartbeat every time, through anything, is not better than one that sometimes says no. It is worse, because it cannot be right for the right reason.
- It changes nothing about movements. Your baby's pattern of movement is the thing that matters, whatever a device picks up.
Many people with an anterior placenta also say movements took longer to become obvious, for the same physical reason. That does not lower the bar. The NHS position is that any change from your baby's usual pattern is worth a call, and it is here.
What Firstsong does differently for you
It tells you it found nothing
In words, with the reason, and with the line that this on its own means nothing is wrong. A blank screen leaves you interpreting silence when you are least equipped to.
It shows clarity, not a fake number
While it listens you see a clarity meter. In a bad spot you can watch it stay low and move the phone, instead of waiting on a number that was never coming.
It does not double your pulse to save face
The easiest way to rescue a hard listen is to quietly report the mother instead. The engine refuses whole number multiples and reads your real pulse as a veto. The long version is here.
The limit, once more. Everything above came from research sensors on the abdomen, not an iPhone microphone against real skin. How much survives that move is the number we do not have, and an anterior placenta is where that gap is likely to be widest.
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Common questions
Will an app work at all if I have an anterior placenta?
Sometimes yes and sometimes no, and we cannot tell you which in advance. Some people get a clear rhythm in the third trimester and some never get anything usable from a phone. What decides it is placental thickness, where the baby is lying and how quiet your room is.
Would a home doppler be better?
It has more power, so a better chance of reaching your baby. That is not the whole question. It will also happily give you a strong, reassuring sound that is the placenta or one of your own vessels. Kicks Count campaigns against home dopplers for that reason, and the objection applies to Firstsong just as much.
Where exactly should I put the phone?
Lower and more to the side than feels natural. Start just above the pubic bone and work out towards one hip, a couple of centimetres at a time, pausing twenty seconds at each spot.
Does the placenta itself make a sound?
Yes. A large volume of your blood moves through it continuously, making a low whoosh at your rate, not the baby's. It is one of the most common things people record and believe is their baby.
Will Firstsong tell me my placenta is at the front?
No. It has no way of knowing and it will not guess. It knows what it can hear and what it cannot, and it tells you which.
Keep reading
- Is it my heartbeat or the baby. the placenta whoosh runs at your rate, and it catches almost everybody
- The long version. the acoustics, written out properly
- Do baby heartbeat apps work. the sceptical question, answered straight
- Hear the difference. the engine live, including a recording it refuses
Last checked 2026-08-23