Fetuses get hiccups because their developing nervous system triggers involuntary contractions of the diaphragm, the thin muscle that separates the chest from the abdomen. These contractions are a reflex controlled by the brainstem, and most pregnant people start feeling them as small, rhythmic jerks between weeks 21 and 24. Far from being a problem, fetal hiccups are one of the earliest signs that the baby’s reflexes and respiratory muscles are maturing on schedule.
How Fetal Hiccups Work
A hiccup, whether in a fetus or an adult, is a reflex arc. The brainstem sends a signal that causes the diaphragm to contract suddenly. In adults, this pulls air in, and the vocal cords snap shut to produce the familiar “hic” sound. In a fetus surrounded by amniotic fluid, the mechanics are the same minus the sound. The diaphragm contracts, generating a brief drop in pressure inside the chest cavity (negative intra-thoracic pressure), and the result is a quick, rhythmic twitch that a pregnant person can feel from the outside.
The reflex is coordinated by the medulla, the part of the brainstem that also manages breathing, heart rate, and swallowing. The fact that a fetus can hiccup means this control center is wired up and functioning, along with the nerves that connect it to the diaphragm and throat. Animal studies have shown that stimulation of the upper throat area can trigger a hiccup-like response through a specific nerve pathway, which suggests that swallowing amniotic fluid may be one of the things that sets off hiccups in the womb.
What Hiccups Do for Development
Scientists don’t have one definitive answer for why this reflex exists, but the leading theories all point to it being useful for the baby’s growth. The most widely discussed idea is that hiccups help train the respiratory muscles. Every time the diaphragm contracts, it gets a small workout. Since a fetus doesn’t breathe air, hiccups (along with other “practice breathing” movements) are one of the few ways the diaphragm and surrounding muscles get exercise before birth. By the time the baby takes a first breath, those muscles have already been contracting regularly for months.
The negative pressure generated inside the chest during a hiccup may also play a role in regulating amniotic fluid. Fetuses constantly swallow amniotic fluid and release it, and the pressure shifts from hiccups could help move small amounts of fluid in and out of the developing lungs. This fluid cycling is important for lung growth. The lungs need to be gently stretched by fluid to develop properly, and hiccups may contribute to that process.
There’s also a neurological angle. Hiccups require coordination between the brainstem, multiple nerves, and the diaphragm. Practicing this reflex arc repeatedly helps strengthen the neural pathways involved, much like how a newborn’s sucking reflex improves with repetition. In this sense, hiccups are a sign that the nervous system is actively developing and testing its connections.
When They Start and What They Feel Like
Fetal hiccups can begin as early as the first trimester, but they’re too faint to feel at that stage. Most pregnant people first notice them between 21 and 24 weeks. They feel like repeated, rhythmic jerky movements, distinct from the rolls, stretches, and kicks that make up normal fetal activity. The rhythm is the key giveaway: hiccups come at regular intervals, typically every few seconds, and a single episode can last anywhere from a minute or two up to 15 or 20 minutes.
Unlike kicks, which tend to be sharp and unpredictable, hiccups feel more like a gentle, pulsing tap in one spot. Some people describe it as a twitching sensation low in the belly. You might even see the rhythmic movement from the outside. They tend to become more noticeable in the second and third trimesters and often decrease in frequency as the due date approaches, though the pattern varies widely from one pregnancy to another.
Are Frequent Hiccups a Concern?
For most pregnancies, the answer is no. A 2012 hypothesis suggested that hiccups in the womb could sometimes be triggered by compression of the umbilical cord, with the idea being that the hiccupping motion might cause the fetus to shift position and relieve the compression. This idea gained some attention online, but the clinical evidence doesn’t support it as a cause for worry.
A 2017 study compared 150 women who experienced stillbirth in the third trimester with 500 women who had healthy pregnancies. About 80 percent of women in both groups reported feeling fetal hiccups, with no significant difference between the two groups. Slightly more women in the stillbirth group recalled daily hiccups (58 percent versus 44 percent), but with nearly half the healthy-pregnancy group also reporting daily hiccups, this difference isn’t meaningful enough to use as a warning sign. Clinicians at UT Southwestern Medical Center have noted that they’ve encountered no published data or clinical experience linking fetal hiccups to poor outcomes.
In short, daily hiccups are common and normal. What matters more is your baby’s overall movement pattern. If you notice a sudden, dramatic change in how much your baby moves overall, that’s worth paying attention to, but hiccups on their own, even frequent ones, are not a red flag.
Hiccups vs. Kicks During Movement Tracking
If you’re doing daily kick counts in the third trimester, you may wonder whether hiccups should count. Most practitioners advise focusing on distinct movements like kicks, rolls, and jabs rather than hiccups, since hiccups are an involuntary reflex and don’t reflect the same kind of voluntary activity. A baby who is hiccupping but otherwise still isn’t necessarily “active” in the way kick counts are designed to measure. When you’re tracking movement, look for the variety of motions your baby normally makes, and treat hiccups as a separate, reassuring sign that the nervous system is doing its job.