While we obviously lack subjective descriptions of intrauterine life, ultrasound has revealed many secrets of the life of the fetus. We know that the fetal kidneys function in utero and that the fetus urinates into the amniotic fluid. The fetus also swallows amniotic fluid, although whether or not to quench its thirst will likely never be known. The intestines are also active, and a thick, viscid, tarlike substance called meconium is found in the lower bowel. Usually, meconium is not excreted until after delivery, although it may be squeezed out of the bowel of a baby in breech presentation, or when the baby has been stressed during labor and delivery.

The fetal movements felt by mother, father, physician, and midwife are usually the thrusting and bending of arms and legs. The motion of the legs is more extensive than that of the arms, so if movements appear most active in the upper abdomen, the head is most likely down.

Dr. Johann Friedrich Ahlfeld, a German scientist, was the first to claim that the fetus sucks its fingers in utero. He reported the case of a child born with a swollen thumb; immediately after birth it put the swollen finger into its mouth and sucked. Now that we have been able to watch babies with sonography, such activity has been recorded on movie film and videotape. The fetus also hiccups somewhat frequently. Mothers can feel or see these movements through the abdomen. They are short, quick, regular jerks of the child's shoulders and trunk, fifteen to twenty a minute. They resemble ordinary hiccups except for the absence of the stridor, the harsh noise. An attack of intrauterine hiccups usually lasts about 15 minutes and may recur several times before birth.

In the very strictest sense the fetus does not breathe in utero simply because there is no air inside the uterus. Exchange of gases between the mother and the baby and therefore between the baby and the outside environment is carried on by the placenta and the maternal circulation. However, steady chest movements of the infant clearly playa role in the development of the lungs. Respiratory movements of the fetal thorax were first observed over 100 years ago by noting a rhythmic rising and falling of the abdominal wall of the mother near the navel.