Bumpology: Why can't my baby sleep when I do?
By Linda Geddes Days to go: 69 Waist size: 96.5 centimetres (38 inches) Thirty weeks into my pregnancy, and I’ve 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 “know” when I wake up in the middle of the night – 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 “appear to be reflective of the advancing development of the nervous system”, says Peter Hepper, a fetal psychologist at Queen’s University Belfast, UK. Fetuses also spend far more of their time in REM or “dreaming” sleep than older infants or adults do. So what’s the purpose of all this sleep, and how closely do my baby’s 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. He adds that there’s little evidence of these cycles following the same pattern as the mother – something I’ll 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. “This may be due to the fact that the muscles in the abdomen relax and the fetus has more room to move about.” As for the function of REM sleep, Allan Hobson, a sleep researcher at Harvard Medical School in Boston, believes REM sleep may be training the brain to “wake up”, 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’t thought to emerge until around 5 years of age, so it seems unlikely that the fetus is “dreaming” in a sense that you or I would recognise. But it’s possible that fetuses could be using REM sleep to rehearse or organise things that they’ve learned during the day, says Hepper. “Given the fetus’s senses are operating and it has the potential to learn, it could be dreaming about the day’s experiences,” he says. Meanwhile, Olivier Walusinski, 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). “Yawning appears to be not just a matter of opening one’s mouth, but a generalised stretching of muscles,” says Walusinski. Fetuses and newborn babies seem to yawn more frequently than adults do – once or twice an hour, compared with around 20 times a day in adults (Frontiers of Neurology and Neuroscience, DOI: 10.1159/000307075). 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’s 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’ tales tell me my baby’s sex?, Active fetus, boisterous child? Uh-oh, Why do I loathe lettuce?. More on these topics: