Fetuses start to yawn from around 11 weeks
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Thirty weeks into my pregnancy, and I鈥檝e noticed a distinct (and slightly annoying) pattern emerging. No sooner am I lying down to go to sleep at night than my baby starts kicking me. She also seems to 鈥渒now鈥� when I wake up in the middle of the night 鈥� even if I stay still. Within minutes of waking, there she is again, launching a volley of kicks against my intestines.
Up to this age, fetuses have spent the majority of time asleep. At around 30 weeks they start to develop organised patterns of sleeping and waking, composed of four distinct states from deep sleep to awake.
These sleep-wake cycles 鈥渁ppear to be reflective of the advancing development of the nervous system鈥�, says , a fetal psychologist at Queen鈥檚 University Belfast, UK. Fetuses also spend far more of their time in REM or 鈥渄reaming鈥� sleep than older infants or adults do.
So what鈥檚 the purpose of all this sleep, and how closely do my baby鈥檚 sleep patterns follow my own? According Hepper, the function of sleep in the fetus is probably similar to that in the adult, where it is thought to play a role in the consolidation of memories and experience.
Sleep cycles
He adds that there鈥檚 little evidence of these cycles following the same pattern as the mother 鈥� something I鈥檒l no doubt be cursing after the birth. Neither does the fetus move about more during the night than during the day, although the mother may notice it more because she is horizontal, and the movements are affecting different organs.
However, the fetus does seem to increase its movements when the mother lies down initially, says Hepper. 鈥淭his may be due to the fact that the muscles in the abdomen relax and the fetus has more room to move about.鈥�
As for the function of REM sleep, , a sleep researcher at Harvard Medical School in Boston, believes REM sleep may be training the brain to 鈥渨ake up鈥�, as many of the same brain areas that are active during waking are also activated during REM sleep.
As for dreaming, the sort of complex dreams that adults experience aren鈥檛 thought to emerge until around 5 years of age, so it seems unlikely that the fetus is 鈥渄reaming鈥� in a sense that you or I would recognise. But it鈥檚 possible that fetuses could be using REM sleep to rehearse or organise things that they鈥檝e learned during the day, says Hepper. 鈥淕iven the fetus鈥檚 senses are operating and it has the potential to learn, it could be dreaming about the day鈥檚 experiences,鈥� he says.
Early yawning
Meanwhile, , a general physician and yawning specialist based in Paris, France, has been investigating a related phenomenon: fetal yawning.
Fetuses start to yawn from around 11 weeks of development, and continue right through until birth (see video). 鈥淵awning appears to be not just a matter of opening one鈥檚 mouth, but a generalised stretching of muscles,鈥� says Walusinski. Fetuses and newborn babies seem to yawn more frequently than adults do 鈥� once or twice an hour, compared with around 20 times a day in adults ().
Yawning also seems to develop before defined sleep-wake cycles, but once these patterns do emerge, each transition from rest to activity seems to be triggered by a yawn, says Walusinski. What鈥檚 more, the brain regions involved in awakening also seem to be stimulated by yawning, so yawning may also be being used as a rehearsal for waking up, he says.
Read previous Bumpology columns: Choosing the sex of your child, Pregnant at the cheese and wine party, Is my baby making me forgetful?, What does an amniotic cocktail taste like?, My fetus is smarter than an earthworm, Ultrasound reveals breastfeeding mechanics, Boxing clever with the kung-fu fetus, Can old wives鈥� tales tell me my baby鈥檚 sex?, Active fetus, boisterous child? Uh-oh, Why do I loathe lettuce?.
