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By Myrah M.
For expectant parents, hearing a baby’s heartbeat can be an exciting, joyful, and reassuring sound. For healthcare professionals, it can be an informative and valuable assessment. Understanding the normal characteristics of fetal heartbeat and how it changes throughout pregnancy can serve as an important and empowering piece of knowledge for new parents and help them feel involved in their baby’s care right from the start. Let’s take a closer look at the different ways to measure a fetal heart rate and how each trimester differs.
During the early stages of embryo development, the heart is one of the first organs to begin forming. Early cardiac (heart) cells begin developing within the first few weeks after conception and a beating, 4-chambered heart is formed usually by 6-7 weeks gestation. This tiny but functional heart is difficult to detect outside of the womb, purely due to its small size and the inability of most dopplers to pick up the faint heartbeat through layers of the mother’s skin, fat tissue, and organs.
An ultrasound wand placed in the mother’s vagina is usually able to get close enough to the developing fetus to pick up the heartbeat during those early weeks. Very early on, the heartbeat may be as low as 100-120 beats per minute (bpm) but quickly increases over the first trimester to an average of 120-180 bpm by 12 weeks. If you are unable to find your baby’s heartbeat on your own with a doppler during the first trimester, don’t worry as this is fairly common. It can even be tricky for trained professionals to locate. If you have concerns, always contact your doctor or midwife to discuss.
During the second trimester, your baby’s heartbeat will become much easier to detect as your baby grows and rises out of the pelvis. The average heart rate slows just a little, with a range of 120-160 bpm. The rate may speed up or slow down within that range based on things like your baby’s activity level, outside stimulation like sounds or movement, and even food the mother has eaten. Brief irregularities in rate may occur here and there as well, but for the most part, the heart rate should hold fairly steady.
Your doctor or midwife will likely check the heartbeat at each prenatal appointment now, and you can more easily find the heartbeat yourself with a home doppler. At this stage of pregnancy, it can usually be found below the mother’s belly button towards the pubic bone and fairly centered. Many parents find it enjoyable to listen to their baby’s heartbeat periodically; this can be an exciting time where everything starts to feel more real, especially when paired with those first detectable movements that many mothers begin to feel during the second trimester.
By this point, the baby has grown quite large and will soon be positioning itself for birth, most commonly head down. This does make the heartbeat much easier to detect, but the baby is so far out of the pelvis now that care must be taken to make sure you are picking up the baby’s heartbeat and not the mother’s from the nearby aorta. A slower rate of 70-100 bpm is likely to be the mother’s heart and you will need to reposition the doppler to find the baby. In a head down baby, the heartbeat can usually be found around or below the mother’s belly button and off to either side depending on which way the baby is facing (you’ll want to try to hear it through the baby's back).
A baby not yet in the head down position may be easier to detect higher up, around the mother’s belly button or slightly above. At this stage, babies can be very active and aware of being prodded with a doppler and may change their position or seem to wiggle away from it, so you may need to be patient. The average heart rate is still between 120-160 bpm at this stage and your doctor or midwife may do some additional monitoring to ensure your baby is responding to late pregnancy changes (like Braxton Hicks contractions or increasingly cramped quarters) without issue. Too much variability in the heart rate or a consistently slow or fast heart rate may indicate an issue with the baby’s position, the umbilical cord, or another problem causing stress to your baby and would warrant further investigation. As always, if you have concerns when trying to monitor your baby’s heartbeat from home, contact your doctor or midwife.
A baby’s heartbeat during labor can tell healthcare professionals a lot about how the baby is tolerating the process, and heart rate monitoring may be much more frequent or even continuous during labor. A portable doppler, an external ultrasound probe fastened to the mother’s belly, or an internal wire placed through the cervix and onto your baby’s scalp are all possible ways your baby’s heart rate can be monitored during labor. It is normal for the baby’s heart rate to change with contractions, especially as the baby descends into the birth canal. How the heart rate changes with contractions (slows down or speeds up), when it changes (before, during, or after a contraction), and how long it takes to get back to a baseline rate all provide valuable information about the baby’s health during labor and can alert your doctor or midwife to any issues that may arise.
A baby’s heartbeat is one of the first signs of early life forming. Once that little heart starts beating, it never stops! It can be an eagerly awaited and reassuring sound for new parents and bring a sense of reality to this exciting time. With proper understanding of how to find it and what to expect during each trimester, hearing your baby’s heartbeat can facilitate bonding, ease worries, and provide a fun way to share the experience with siblings, grandparents, or other family and friends. Happy listening!