Babies hiccup in the womb because their developing diaphragm contracts involuntarily, just as it does after birth. These tiny spasms can start as early as the first trimester, though most parents don’t feel them until around 21 to 24 weeks. They’re almost always harmless and may actually serve a purpose in preparing your baby’s body for breathing.
How Fetal Hiccups Work
A hiccup is a sudden, involuntary contraction of the diaphragm, the dome-shaped muscle that separates the chest from the abdomen. In a fetus, the diaphragm acts much like it will after birth, pushing the belly outward and downward with each contraction. Unlike adult breathing, where you see the chest rise and fall, fetal and newborn breathing movements center on the belly. Hiccups follow that same rhythmic motion but with more force, producing the distinctive repetitive jerks you can feel from the outside.
Because the baby is surrounded by amniotic fluid rather than air, these contractions don’t produce any sound or serve the same function as a postnatal hiccup. Instead, small amounts of amniotic fluid move in and out of the lungs with each spasm.
Why It Happens: Leading Theories
Scientists don’t have a single definitive explanation for fetal hiccups, but several well-supported theories exist.
The most widely discussed idea is that hiccups provide exercise for the respiratory muscles. By repeatedly contracting the diaphragm before birth, the baby essentially trains the muscle it will need for breathing air. This “practice” may help the lungs and surrounding muscles mature so they’re ready to function immediately at delivery.
A second theory ties hiccups to the umbilical cord. A 2012 analysis published in BMC Pregnancy and Childbirth proposed that hiccups could be a protective response to cord compression. When the umbilical cord gets temporarily kinked or pressed, blood flow to the baby drops slightly. Hiccupping may cause the baby to shift position, relieving pressure on the cord and restoring normal circulation. Animal research supports this link: in sheep, intermittent umbilical cord compression triggered fetal hiccups.
A third possibility involves swallowing. Babies regularly swallow amniotic fluid throughout pregnancy, which helps develop the digestive system. Some researchers believe this swallowing, or the occasional aspiration of waste particles in the fluid, can irritate the diaphragm and trigger a hiccup episode.
When Hiccups Start and How Often They Happen
Fetal hiccups have been detected on ultrasound as early as the first trimester, though episodes become more noticeable and frequent during the third trimester. Interestingly, the frequency tends to decrease as pregnancy progresses, particularly after 28 weeks. This may reflect the maturing nervous system gaining better control over involuntary reflexes.
Most pregnant people begin feeling hiccups between 21 and 24 weeks. Early on, they’re easy to miss or to confuse with other movements. By the late second trimester and into the third, the sensation is more distinct, and many parents notice one to a few episodes per day. Each bout typically lasts anywhere from a couple of minutes to about 15 minutes.
How to Tell Hiccups From Kicks
Fetal hiccups feel like small, rhythmic, repetitive jerks or pulses in one spot. They have a steady, almost metronome-like quality. You’ll notice they come at regular intervals, every two to three seconds, and they stay in roughly the same location in your belly.
Kicks and stretches feel different. Around 25 to 28 weeks, your baby starts kicking and stretching more forcefully, and those movements are irregular in both timing and location. A kick might hit your ribs, then a few seconds later you feel pressure low in your pelvis. By 30 to 32 weeks, movements shift toward more squirming, jabbing, and kicking rather than the full-body turning of earlier weeks. If the movement you’re feeling has a clear rhythm and repeats in the same spot, it’s almost certainly hiccups.
When Hiccups Could Signal a Problem
In the vast majority of cases, fetal hiccups are completely normal and nothing to worry about. They’re a sign of a developing nervous system doing exactly what it should.
The one situation worth paying attention to is a noticeable change in pattern late in pregnancy. After about 32 weeks, if you’re feeling more than four episodes of hiccups in a single day, or if the hiccups suddenly seem much stronger or more frequent than what you’ve been used to, it’s worth mentioning to your provider. Research in animal models has linked frequent, persistent hiccups after 28 weeks with possible intermittent cord compression. This doesn’t mean something is wrong, but a brief evaluation (usually a non-stress test or ultrasound) can confirm the baby is doing well.
Outside of that specific scenario, fetal hiccups are one of the most benign and common movements you’ll feel during pregnancy. Some babies hiccup multiple times a day, others rarely. Both patterns fall within the normal range.