Another one to add to the list of unusual but interesting questions asked during pregnancy (by my friend Cate): “why are babies supposed to go into the head down position? Doesn’t that make the blood rush into their heads…?!”
There is plenty of information in books and the internet that describe the ideal position in detail, including various exercises you can try in order to chivvy your baby there if they are not head down already. However, it has been difficult to find anything official that really explains why. As the NHS says, sometimes the baby’s head does not “engage” in the pelvis until labour starts, so do these babies get extra blood-flow-around-the-head time while are ones like mine who engaged around week 33 becoming progressively more dizzy? Surely not.
Upside down baby since 33 weeks
Babycentre describes the benefits of the ideal head down or “anterior” position, with the back towards the mother’s front (back to back can cause issues such as backache and a longer labour), as follows:
- The top of your baby’s head puts rounded, even pressure on the neck of your uterus (cervix) during contractions. This helps your cervix to widen and helps to produce the hormones you need for labour.
- At the pushing stage, your baby moves through your pelvis at an angle so that the smallest area of his head comes first. Try putting on a tight polo-neck top without tucking in your chin and you’ll understand how this works!
- When your baby gets to the bottom of your pelvis, he turns his head slightly so that the widest part of his head is in the widest part of your pelvis. The back of his head can then slip underneath your pubic bone. As he is born, his face sweeps across the area between your vagina and back passage (the perineum).
So far, so sensible: it sounds like the head down position is optimal for birth. But what about beforehand? As I sit typing this, I can’t stop imagining how being held upside down for weeks on end would feel!
It turns out that Cate is not the first person to have asked this question. And unsurprisingly, my vague response of “it’s something to do with it swimming in water” has absolutely nothing to do with the real answer. At least it wasn’t just me: this thread on Mumsnet includes all sorts of theories that ultimately point towards a very helpful Wiki Answers page:
“First, the movement downward is slow, over days to weeks, so the baby adjusts to the ‘head-down’ bloodflow, much like astronauts become acclimated to weightlessness over time. Second… the infant’s heart rate is much higher than a “normal” for an adult. While adults have a normal heart rate of about 80 (give or take 10 beats), a fetal to infant’s heart rate is normally 140 to 160. This keeps the fetus well-perfused (i.e. an adequate amount of circulating blood) to the brain and all extremities and vital organs, regardless of the position within the womb.”
There we go then – it’s all to do with the baby’s rapid heartbeat, which keeps the blood circulating around merrily whether the baby is head down or not. One less thing to worry about!