Fetal hiccups can show up as early as the first trimester, but they usually show up around the second or third trimester. When a fetus hiccups, the mother feels little spasms in her belly that are different from other pregnancy movements. Almost all women will feel their fetus hiccuping at least once during the pregnancy, if not more. Some babies will hiccup on a daily basis and others even more frequently.
A contracting diaphragm can trigger hiccups in mature fetuses. In order for a fetus to hiccup in the womb, its central nervous system must be complete. The central nervous system gives the fetus the ability to breathe in amniotic fluid. A hiccup results when the fluid enters and exits the fetus’s lungs, causing the diaphragm to contract rapidly. Fetal hiccups are quite common and can often be seen on an ultrasound as jumping or rhythmic movements. Fetal hiccups are reflexive and do not appear to cause discomfort. In addition, hiccups prepare the fetus’s lungs for healthy respiratory function after birth and they help regulate the baby's heart rate during the third trimester.
Occasionally fetal hiccups can occur when the fetus is not getting enough air. If a woman notices a sudden decrease in the frequency, intensity or length of the fetal hiccups than she seek medical attention right away to check for an umbilical cord compression. A cord compression occurs when the umbilical cord wraps around the fetus’s neck, cutting off the air supply. When the cord wraps around the fetus’s neck, the fetal heart rate increases and blood flow from the umbilical cord to the fetus declines. Cord compression is rare and usually happens over time as the fetus moves within the womb.
A mature fetus may hiccup as he or she develops the reflex that will allow him or her to suckle or drink from the mother’s breast after birth. Once the fetus is born, the suckling reflex will prevent milk from entering the baby’s lungs.