I came across this fascinating article. Even if you're not expecting you might find it interesting. Maybe it's because I'm a psychology major, but I just think all of this is so cool! I copied some of the highlights below.
Tasting and Smelling
"Until recently, no serious consideration was given to the possibilities for olfaction in utero, since researchers assumed smelling depended on air and breathing. However, the latest research has opened up a new world of possibilities.
"The nose develops between 11 and 15 weeks. Many chemical compounds can cross the placenta to join the amniotic fluid, providing the fetus with tastes and odors. The amniotic fluid surrounding the fetus bathes the oral, nasal, and pharyngeal cavities, and babies breathe it and swallow it, permitting direct access to receptors of several chemosensory systems: taste buds in three locations, olfactory epithelia, vomeronasal system, and trigeminal system (Smotherman and Robinson, 1995).
"Associations formed in utero can alter subsequent fetal behavior and are retained into postnatal life. The evidence for direct and indirect learning of odors in utero has been reviewed by Schaal, Orgeur, and Rogan (1995). They point to an extraordinary range of available odiferous compounds, an average of 120 in individual samples of amniotic fluid! In one experiment, babies registered changes in fetal breathing and heart rate when mothers drank coffee, whether it was caffeinated or decaffeinated. Newborns are drawn to the odor of breastmilk, although they have no previous experience with it. Researchers think this may come from cues they have learned in prenatal life."
Listening and Hearing
"Sounds have a surprising impact upon the fetal heart rate: a five second stimulus can cause changes in heart rate and movement which last up to an hour. Some musical sounds can cause changes in metabolism. "Brahm's Lullabye," for example, played six times a day for five minutes in a premature baby nursery produced faster weight gain than voice sounds played on the same schedule (Chapman, 1975).
Researchers in Belfast have demonstrated that reactive listening begins at 16 weeks g.a., two months sooner than other types of measurements indicated. Working with 400 fetuses, researchers in Belfast beamed a pure pulse sound at 250-500 Hz and found behavioral responses at 16 weeks g.a.--clearly seen via ultrasound (Shahidullah and Hepper, 1992). This is especially significant because reactive listening begins eight weeks before the ear is structurally complete at about 24 weeks.
These findings indicate the complexity of hearing, lending support to the idea that receptive hearing begins with the skin and skeletal framework, skin being a multireceptor organ integrating input from vibrations, thermo receptors, and pain receptors. This primal listening system is then amplified with vestibular and cochlear information as it becomes available. With responsive listening proven at 16 weeks, hearing is clearly a major information channel operating for about 24 weeks before birth."
"In utero, eyelids remain closed until about the 26th week. However, the fetus is sensitive to light, responding to light with heart rate accelerations to projections of light on the abdomen. This can even serve as a test of well-being before birth. Although it cannot be explained easily, prenates with their eyelids still fused seem to be using some aspect of "vision" to detect the location of needles entering the womb, either shrinking away from them or turning to attack the needle barrel with a fist (Birnholz, Stephens, and Faria, 1978). Similarly, at 20 weeks g.a., twins in utero have no trouble locating each other and touching faces or holding hands!"
Senses in Action
"Ultrasonographers have recorded fetal erections as early as 16 weeks g.a., often in conjunction with finger sucking, suggesting that pleasurable self-stimulation is already possible. In the third trimester, when prenates are monitored during parental intercouse, their hearts fluctuate wildly in accelerations and decelerations greater than 30 beats per minute, or show a rare loss of beat-to-beat variability, accompanied by a sharp increase in fetal movement (Chayen et al, 1986). This heart activity is directly associated with paternal and maternal orgasms! Other experiments measuring fetal reactions to mothers' drinking one ounce of vodka in a glass of diet ginger ale show that breathing movements stop within 3 to 30 minutes. This hiatus in breathing lasts more than a half hour. Although the blood alcohol level of the mothers was low, as their blood alcohol level declined, the percentage of fetal breathing movements increased (Fox et al, 1978).
"Babies have been known to react to the experience of amniocentesis (usually done around 16 weeks g.a.) by shrinking away from the needle, or, if a needle nicks them, they may turn and attack it. Mothers and doctors who have watched this under ultrasound have been unnerved. Following amniocentesis, heart rates gyrate. Some babies remain motionless, and their breathing motions may not return to normal for several days.
"Finally, researchers have discovered that babies are dreaming as early as 23 weeks g.a.when rapid eye movement sleep is first observed (Birnholz, 1981). Studies of premature babies have revealed intense dreaming activity, occupying 100% of sleep time at 30 weeks g.a., and gradually diminishing to around 50% by term. Dreaming is a vigorous activity involving apparently coherent movements of the face and extremities in synchrony with the dream itself, manifested in markedly pleasant or unpleasant expressions. Dreaming is also an endogenous activity, neither reactive or evoked, expressing inner mental or emotional conditions. Observers say babies behave like adults do when they are dreaming (Roffwarg, Muzio, and Dement 1966)."