Some of my patients are startled when they see an ultrasound of their baby and it appears that the baby has its mouth open. In addition to turning over and moving their hands and feet, babies do open and close their mouths in the womb. The fetus may also suck its thumb or finger.
Digestive System Develops
By 21 weeks, the fetal digestive system has developed enough to allow the fetus to swallow amniotic fluid. The fetus absorbs much of the water in the swallowed fluid. Hydrochloric acid and adult digestive enzymes are present in small amounts in the fetal digestive system at 21 weeks.
Researchers believe swallowing amniotic fluid may help growth and development of the fetal digestive system. It may also condition the digestive system to function after birth. By the time a baby is born, he or she may swallow large amounts of amniotic fluid, as much as 17 ounces (500ml) of amniotic fluid in a 24-hour period.
Your baby can open its eyes inside the uterus. Eyelids cover the eyes and are fused or connected around 11 to 12 weeks. They remain fused until about 27 to 28 weeks, when they open.
A baby can hear inside the womb, before it is born. Life inside the womb may be like living near a busy freeway. The developing baby hears a constant background of digestive noises and the maternal heartbeat. The mother-to-be's voice is also heard, although the fetus may not hear higher-pitched tones. There is evidence that by the third trimester the fetus responds to sounds it hears. Researchers have noted fetal heart-rate increases in response to tones it hears through the mother's abdomen. Newborns have been found to prefer their mother's voice to a stranger's, which suggests they recognize the mother's voice. They have also been found to prefer their mother's native language, and they respond strongly to a recording of an intrauterine heartbeat.