Babies hiccup in the womb because their developing nervous system triggers involuntary contractions of the diaphragm, the thin muscle that controls breathing. These hiccups can start as early as the first trimester and are a normal part of fetal development. Most pregnant women begin feeling them between weeks 21 and 24 as repeated, rhythmic jerky movements in the belly.
How Fetal Hiccups Work
A hiccup is a reflex, not a voluntary movement. It originates in the brainstem, specifically the medulla, which sends a signal down to the diaphragm causing it to contract suddenly. This contraction creates a brief burst of negative pressure inside the chest. The reflex follows the same basic arc in a fetus as it does in an adult: a trigger activates the nerve pathway, the diaphragm spasms, and the characteristic “hic” follows. In a fetus surrounded by amniotic fluid rather than air, the sensation is the same muscular twitch without the audible sound you’d hear after birth.
What makes fetal hiccups particularly interesting is that they appear to serve a developmental purpose rather than being a pointless quirk of biology.
Hiccups Help Train the Brain
Research from University College London found that each time a newborn hiccups, it triggers a large wave of brain signals. The diaphragm contraction produces a pronounced response in the brain’s cortex: two large brainwaves followed by a third. That third wave resembles the brain’s response to sound, which suggests the baby’s brain may be learning to connect the physical sensation of the diaphragm contracting with the “hic” sound it produces.
This matters because it helps the brain build the circuits that will eventually allow voluntary control of breathing. At birth, the neural networks that process body sensations are not fully developed. Hiccups give the brain repeated practice linking a muscle contraction to a sensory experience, which is a crucial milestone for establishing those connections. In other words, those little rhythmic jolts in your belly are your baby’s nervous system rehearsing for life outside the womb, learning how to monitor and control the diaphragm so that breathing becomes something the brain can regulate on its own.
When They Start and How Often They Happen
Fetal hiccups have been detected on ultrasound as early as the first trimester, though they’re far too faint for a mother to notice at that stage. Most women start feeling them around weeks 21 to 24 as small, repetitive jerks that are distinct from the broader rolls and kicks of normal fetal movement. Their frequency increases during the third trimester, which lines up with the period of most rapid brain and nervous system development.
Individual episodes can last anywhere from about a minute to an hour. There’s wide variation between pregnancies. Some women feel hiccups multiple times a day while others notice them only occasionally. Both patterns fall within normal range.
How to Tell Hiccups From Kicks
Fetal hiccups feel different from other movements in a few distinct ways. Kicks and punches tend to be isolated, sharp, and unpredictable in timing. Hiccups are rhythmic and repetitive, coming at regular intervals much like your own hiccups do. They often feel like a pulsing or tapping sensation concentrated in one area of the belly rather than the sweeping, rolling movements you get when a baby shifts position.
You may even see the rhythmic twitches from the outside, especially later in pregnancy when the baby is larger and closer to the abdominal wall. If you’re unsure whether what you’re feeling is hiccups or kicks, timing the pattern usually makes it clear. A steady pulse every few seconds that continues for several minutes is almost certainly hiccups.
Are Frequent Hiccups a Concern?
For the vast majority of pregnancies, fetal hiccups are completely harmless. Some older animal studies raised the idea that hiccups might be triggered by umbilical cord compression, with researchers speculating that the spasms could prompt a fetus to shift away from a compressed cord. However, those studies were conducted in fetal sheep, and the findings have never been replicated or confirmed in human research.
A 2017 study compared 150 women who experienced third-trimester stillbirths with 500 women who had healthy pregnancies. Roughly 80 percent of women in both groups remembered experiencing fetal hiccups, with no significant difference between the two groups. This suggests fetal hiccups are not associated with adverse pregnancy outcomes. Clinicians at UT Southwestern Medical Center have noted that no published research or clinical experience has linked fetal hiccups to problems like preterm birth or stillbirth.
That said, a general guideline worth knowing: hiccups typically become less frequent as you approach full term. If your baby continues to hiccup daily after about week 32, with episodes lasting longer than 15 minutes, or if you notice three or more distinct hiccup episodes in a single day, it’s reasonable to mention it at your next appointment. This isn’t because hiccups themselves are dangerous, but because any significant change in fetal movement patterns is worth tracking.
Why Hiccups Continue After Birth
If fetal hiccups seem frequent, newborn hiccups can feel even more so. Babies hiccup a lot in their first few months of life, and for the same reason they did in the womb: the brain is still building its sensory map of the body. Each hiccup reinforces the neural connection between the diaphragm’s contraction and the brain’s awareness of that contraction. As these circuits mature and breathing regulation becomes more automatic, hiccup frequency gradually declines. By adulthood, hiccups are relatively rare and serve no known purpose, a leftover from a reflex that did its important work long before you could remember it.