According to Fetal Movement

According to an overview produced by the Royal College of Physicians of Edinburgh, purposive movement begins at about 18 weeks, gradually replacing reflex movements

but in the same article says

At week 11, the fetus can open its mouth and suck its fingers; at week 12, it begins to swallow amniotic fluid.

I highly doubt that open a mouth and suck its fingers can be classified as "reflex movements", then how it is asserted that there is not purpose movement in the fetus until week 18 when a fetus can open its mouth and suck its fingers at week 11?

  • 4
    $\begingroup$ Why do you doubt that finger-sucking is a reflex? $\endgroup$
    – arboviral
    Commented Jun 11, 2018 at 13:35
  • $\begingroup$ Did you ever put a finger in an infant's mouth :) It's about as reflexive as it can be. +1 for a well researched question though $\endgroup$
    – AliceD
    Commented Jun 11, 2018 at 18:22

1 Answer 1


Swallowing (Nishino, 2013) and sucking (rooting reflex) are reflexes. The fingers may just happen to be in the vicinity of its oral region (they often are; Fig. 1.), and oh boy are babies keen to grab a nipple when it's close! Mouth openings can henceforth be also reflexive, being part of the rooting reflex.

hands on head
Fig. 1. Fetal hands in facial area. sourceL: ABC News

- Nishino, Front Physiol (2012); 3: 4892013


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