Unborn babies get hiccups because their diaphragm, the main breathing muscle, contracts in quick, rhythmic bursts while they’re still developing in the womb. These contractions are part of how the body practices and refines the movements it will need for breathing, feeding, and other functions after birth. Most pregnant people start feeling fetal hiccups between weeks 21 and 24, and they’re a normal, healthy sign of development.
How Fetal Hiccups Work
The diaphragm is a dome-shaped muscle that sits below the lungs. With each breath, it contracts and moves downward, pulling air into the lungs and pushing the abdomen outward. In an unborn baby, the diaphragm starts working the same way it will after birth, even though the baby isn’t breathing air yet. Hiccups follow that same rhythmic motion as breathing, but more forcefully, creating repeated involuntary contractions.
These contractions are controlled by a reflex arc centered in the brainstem. The diaphragm spasms, the baby’s body jerks, and because the baby is surrounded by amniotic fluid rather than air, the hiccup plays out as a quick, rhythmic pulsing that you can feel from the outside. Unlike kicks or rolls, which tend to be irregular and vary in intensity, hiccups feel like steady, evenly spaced jerky movements, almost like a ticking clock in your belly.
What Hiccups Do for Development
Scientists have proposed several explanations for why fetal hiccups exist, and the most compelling ones point to them as a kind of training exercise for the body and brain.
One leading theory is that hiccups give the respiratory muscles a workout. The baby’s lungs aren’t inflating with air yet, but the diaphragm still needs to build strength and coordination for the moment of birth. Repeated contractions during hiccups may help condition these muscles so they’re ready to support breathing from the very first breath.
Research from University College London found that each hiccup triggers a large wave of electrical activity in the brain’s cortex. In newborns, the team recorded two large brainwaves followed by a third every time the diaphragm contracted during a hiccup. That third wave resembled the kind of brain signal produced by hearing a sound, suggesting the brain may be connecting the “hic” sound with the physical sensation of the diaphragm moving. This process could help babies learn to sense and eventually control their breathing muscles voluntarily. The circuits that process body sensations aren’t fully developed at birth, so hiccups may play a role in building those neural connections.
A separate theory proposes that hiccups serve as a natural burping reflex. The forceful diaphragm contraction creates a brief vacuum in the chest that could pull swallowed air out of the stomach. For newborns, this would be a significant advantage during feeding, since clearing air from the stomach makes room for more milk. This may also explain why hiccups are far more common in infants than adults: once feeding patterns mature and the nervous system develops, the reflex becomes less necessary.
When They Start and How Often They Happen
You’ll typically begin to notice fetal hiccups between 21 and 24 weeks of pregnancy. Early on, they may feel like faint flutters that are hard to distinguish from other movements. As the baby grows larger in the second and third trimesters, the sensation becomes more distinct: a predictable, repetitive tapping or pulsing, usually felt low in the abdomen.
Individual hiccup sessions can last anywhere from about one minute to an hour. Some babies hiccup several times a day, others less frequently. Both patterns are normal. Hiccups tend to become more noticeable as pregnancy progresses, partly because the baby is bigger and partly because the nervous system is more developed and producing stronger contractions.
How to Tell Hiccups From Kicks
Kicks, punches, and rolls feel irregular. They come and go unpredictably, vary in strength, and can happen in different spots as the baby shifts position. Hiccups, by contrast, have a metronome-like quality. They repeat at a consistent interval and stay in the same location because the baby’s torso isn’t moving around between contractions. If you place your hand on your belly and feel a steady, rhythmic pulse every few seconds, that’s almost certainly hiccups.
When Frequent Hiccups Deserve Attention
Fetal hiccups are overwhelmingly normal and not associated with adverse pregnancy outcomes. An older theory suggested that hiccups might be triggered by compression of the umbilical cord, based largely on animal studies in sheep where cord compression did produce hiccupping. However, this theory hasn’t been supported by broader clinical data in humans.
That said, a reasonable guideline is to pay attention if you notice more than four episodes of hiccups in a single day after about 32 weeks, or if the hiccups suddenly feel much stronger or more frequent than what you’ve been used to. In those cases, letting your provider know is worthwhile so they can check on the baby’s well-being. A significant, sudden change in any type of fetal movement pattern, whether it’s more or less activity than usual, is always worth mentioning.
For the vast majority of pregnancies, though, those little rhythmic jolts are simply a sign that your baby’s diaphragm, lungs, brain, and nervous system are doing exactly what they’re supposed to do.