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Foetal Motor Development

Gestational Period

The gestational period in single pregnancies lasts 40 weeks on average.[1] For many years, "term pregnancy" was used for babies delivered between 37 and 42 weeks. However, outcomes for newborns vary depending on the timing of their delivery within this five-week range. The following designations have been established to address this variability:[1]

  • early term: 37 0/7 to 38 6/7 weeks of gestation
  • full term: 39 0/7 to 40 6/7 weeks of gestation
  • late term: 41 0/7 to 41 6/7 weeks of gestation
  • postterm: 42 0/7 weeks of gestation and beyond

Preterm is defined as babies who are born before 37 weeks of gestation.[2] Nearly 11% of all births worldwide are preterm.[3] Within this, there are subcategories: extremely preterm are babies born before 28 weeks; very preterm are babies born between 28 and less than 32 weeks; and moderate to late preterm are babies born between 32 and 37 weeks.[4] 75% of all preterm births are late preterm births (i.e. born between 34 0/7 and 36 6/7 weeks).[5]

Stages of Prenatal Development

The following table summarises the stages of prenatal development.

Table 1. Stages of Prenatal Development[6][7]
Period Time Features
Germinal period Fertilisation to 2 weeks
  • Shortest stage
  • Begins at conception when sperm fertilises the egg, forming a zygote
  • The zygote moves to the uterus, during which time it divides a number of times, creating two structures, which become the embryo and placenta
  • It becomes a blastocyst that implants into the uterine lining
Embryonic period Weeks 2 to 6 or 8
  • Arms and legs start to develop from around week 6
  • Development of organs and structures (e.g. neural tube, eyes, head, mouth)
  • Heart develops with pulse starting from around 6 weeks
  • The embryo has plenty of space to move in the amniotic sac
Foetal period Week 9 to birth
  • Ongoing differentiation of limbs and cell types
  • Organs and systems continue to develop
  • Eyelashes, hair and fingernails start to grow
  • Increased movement (see discussion below for more detail)
  • By weeks 14-15, the baby has all of the preliminary feeding movements present (hands to mouth)
  • By 4 months, hands together
  • Reduction in space by 5 months, with baby adopting a curled-up position (called physiologic flexion at birth)
  • Sucking at 6 months (potentially thumb sucking)
  • As the baby continues to grow, there is less and less space, which provides deep-pressure feedback for the baby
  • Also receive vestibular input when the mother is walking around

For babies born preterm, "their environmental experiences in a NICU environment are going to be very drastically different [to a full term baby]. So those early stages of development are going to look a lot different in a preterm versus a term baby."[6] -- Krista Eskay

Nervous System Maturation

Synaptogenesis, or the formation of synapses, "is integral for creating brain networks, and for the overall architecture of brain connectivity."[8]

Synaptogenesis increases significantly during the third trimester. There is then an “explosive increase” in the neonatal period, peaking during the first two years of life.[8] This period is called synaptic blooming, and there is a lot of neural growth and the proliferation of dendrites.[6]

“What's happening in these early, early years from prebirth and that prenatal period all the way through toddlerhood is that we are making thousands of new connections [...] How mature the nervous system is at any different stage in [a child’s] development [...] has huge influences on what we can and cannot do based on whether or not our nervous system is ready to be able to perform these new tasks based on [...] how many connections have been formed.”[6] -- Krista Eskay

Experience-expectant plasticity: “Some inputs are essentially universal—except under very extreme conditions, every human child experiences gravity, a caregiver, exposure to variations in temperature, and so on.”[9] These inputs result in experience-expectant plasticity.[9] Experience-expectant plasticity largely occurs during the first few months of life.[10] Experience-dependent plasticity: Some inputs vary, and this results in “differences in structures, processes, and skills”[9] (e.g. learning to catch because someone plays ball with you a lot, or learning to play the piano because you had the opportunity to practise the piano[6]). Experience-dependent plasticity occurs throughout life.[10]

“So you can see you have these things that we want to happen during these developmentally sensitive periods. You don't have to be taught how to feed, but you need the opportunity and exposure to that situation in order to continue to do it appropriately and develop that skillset [...] So you can almost think about it [as] nature versus nurture. So your nature is this kind of experience-expectant plasticity, those things that we're genetically coded to do, and then have the opportunity to then do them versus [...] your nurture where you're being provided with particular opportunities to learn new specific skills.”[6] – Krista Eskay

Patterned Movements

The sensorimotor system starts to develop during gestation, which leads to patterned movements.[11] Foetal movements may be isolated (a specific pattern) or general (involve multiple body parts). In the later stages of pregnancy, these movement patterns become more complex.[11][12]

Major systems within the brain are entrenched prior to birth and facilitate the infant's emerging developmental skills. The motor and sensory systems are among the earliest systems to mature. They help the infant interact with and receive input from the world.[13]

First Motor Patterns

In the first few weeks of gestation, the most common motor patterns are spontaneous startles, general movements, isolated movements and twitches.[14] By week 13, a foetus's motor activity can include jaw movements, swallowing, yawning, and hand-face contact. During this period, handedness preference can be observed.[14]

Startles

Startles are whole body movements that begin in the limbs and spread to the neck and trunk.[15] Startles are brief in nature and begin at 8 weeks gestation.[15] [16] From this time, they increase in frequency until they reach a peak. There is a strong decrease in the number of startles up to 17 weeks gestation and a more gradual decrease throughout the rest of the pregnancy.[16]

General Movements

General movements are whole body movements that are slower and more complex than startles.[15] This movement pattern also emerges around 8 weeks and is characterised by their variety and fluency of movement. It has been argued that the displacement caused by a startle may lead to a chain of counter-reactive movements and trigger general movements.[16] By the 17th week of gestation, general movements appear spontaneously and do not necessarily follow a startle.[16][17]

Isolated movements

Isolated movements emerge shortly after general movements. These movements involve the unique sequencing of specific body parts. By the 14th week, isolated movements occur more frequently than general movements. Distinctive movements of the arms and legs start at the same time. However, arm movements occur more frequently than leg movements.[16]

Arm extension along with finger extension can be seen from 12 weeks gestation onwards. During this time, a foetus's hand consistently touches its face, head and occasionally its mouth. Distinctive finger movements appear around 13 weeks. By the third trimester, the foetus is able to squeeze and manipulate the umbilical cord.[15]

Slow or rapid isolated leg movements can occur bilaterally in an alternating pattern or unilaterally as a sporadic kick.[15]

Twitches

Twitches are a type of spontaneous motor activity that occur during active sleep. This brief motor activity causes contractions of muscles, resulting in quick flexion or extension movements of the neck or limbs. Twitches can be seen in foetuses at around week 10-12, and they increase in frequency from weeks 15-16.[16]

Sensation

It can be difficult to determine when a foetus's motor activity is related to sensation. Spontaneous motor behaviour and reflexive reactions to touch emerge at around the same time, firstly around the mouth. Non-reflexive responses to stimulation occur as the sensory systems develop. It is possible to observe a foetus respond by moving to sound, light and touch disturbances. From around 21-33 weeks, foetuses can respond to maternal touch of the stomach.[16]

Random Movements

The first movements of a foetus are spontaneous and random in nature. Random movement can be referred to as motor babbling. While this motor activity is not goal-oriented, it allows the foetus to explore the environment around them and the significance of its movement on the environment. In the later stages of pregnancy, as the available space decreases, there is a reduction in the amount of movement.[16] Movements are confined to rotation and extension of the spine. This decrease in general movements coincides with an increase in facial movements. During this time, foetuses can be observed chewing, opening and closing the jaw and swallowing. This shift in movement patterns is seen as progression of normal foetal development.[14]

Goal-Directed Movements

Initial isolated movements tend to be towards body parts that are highly innervated such as the face. By 10 weeks gestation, a foetus regularly touches its face. As the pregnancy advances, arm movements towards the mouth increase. It has been hypothesised that foetuses might like to suck their thumb because both the mouth and thumb are richly innervated.[16] Foetuses also have a preference for rubbing their eyelids, scratching their temples with their fingers and touching their feet, particularly the soles which are highly innervated.[16]

Goal-oriented behaviour can be seen when the foetus brings its arms to its mouth or eyes. Studies have shown that foetuses anticipate their hand coming to their mouth by opening their mouth before the hand arrives. Other studies report foetuses tend to slow down their arm speed as they bring it towards their eyes.[17] These goal-oriented movements tend to increase as gestation progresses.[16]

Foetal Posture

Many people assume the foetus is only in a flexed position in utero. However, a foetus changes its posture and position quite frequently. The posture of the foetus can be upside down, upright, sitting, prone or supine. This variability in movement is most common in the first half of the pregnancy. Alternating leg movements or somersaults typically initiate rotational motion along the longitudinal axis of the foetus. Additionally, during the first 20 weeks of gestation, foetuses can cross their legs and raise their hands and place them behind their head.[15]

Facial Expressions

In early pregnancy, complex sequential foetal eye movements can be observed. Between 23-26 weeks, blinking-like movements occur as the foetus opens and closes their eyelids. Clusters of rapid eye movements occur around 30 weeks onwards. In the last trimester of pregnancy, the foetus can be seen smiling, scowling and pouting.[15]

Stretches and Yawns

Yawning and stretching are initiated at around 12 weeks gestation. These are both complex motor patterns. Yawns begin with a wide opening of the jaw, a simultaneous caudal movement of the tongue and retroflexion of the head. This whole process takes around 9-13 seconds. Stretching involves the combination of head retroflexion, arm elevation in an externally rotated fashion and trunk extension. This complex movement pattern is always slow.[15]

Resources

References

  1. ↑ 1.0 1.1 ACOG Committee Opinion No 579: Definition of term pregnancy. Obstet Gynecol. 2013 Nov;122(5):1139-1140.
  2. ↑ Stevenson DK, Winn VD, Shaw GM, England SK, Wong RJ. Solving the Puzzle of Preterm Birth. Clin Perinatol. 2024 Jun;51(2):291-300.
  3. ↑ Crump C, Sundquist J, Sundquist K. Preterm or early term birth and risk of attention-deficit/hyperactivity disorder: a national cohort and co-sibling study. Ann Epidemiol. 2023 Oct;86:119-125.e4.
  4. ↑ World Health Organization. Preterm birth. Available from: https://www.who.int/news-room/fact-sheets/detail/preterm-birth (accessed 9 April 2025).
  5. ↑ Kashani-Ligumsky L, Neiger R, Segal E, Cohen R, Lopian M. Is parity a risk factor for late preterm birth? Results from a large cohort study. J Clin Med. 2024 Jan 12;13(2):429.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 Eskay K. Foetal Motor Development Course. Plus, 2023.
  7. ↑ Cleveland Clinic. Fetal Development. Available from: https://my.clevelandclinic.org/health/articles/7247-fetal-development-stages-of-growth (last accessed 31 October 2023).
  8. ↑ 8.0 8.1 Lockwood Estrin G, Bhavnani S. Brain development: structure. In: Benson JB. Encyclopedia of infant and early childhood development (Second Edition). Elsevier, 2020. p.205-14.
  9. ↑ 9.0 9.1 9.2 Oakes LM. Plasticity may change inputs as well as processes, structures, and responses. Cogn Dev. 2017 Apr;42:4-14.
  10. ↑ 10.0 10.1 Sadegh-Zadeh SA, Bahrami M, Soleimani O, Ahmadi S. Neural reshaping: the plasticity of human brain and artificial intelligence in the learning process. Am J Neurodegener Dis. 2024 Dec 25;13(5):34-48.
  11. ↑ 11.0 11.1 Prechtl HF. R.(1986). Prenatal motor development. Motor Development.
  12. ↑ Ji L, Majbri A, Hendrix CL, Thomason ME. Fetal behavior during MRI changes with age and relates to network dynamics. Hum Brain Mapp. 2023 Mar;44(4):1683-1694.
  13. ↑ Thomason ME, Hect J, Waller R, Manning JH, Stacks AM, Beeghly M, Boeve JL, Wong K, Van Den Heuvel MI, Hernandez-Andrade E, Hassan SS. Prenatal neural origins of infant motor development: Associations between fetal brain and infant motor development. Development and psychopathology. 2018 Aug;30(3):763-72.
  14. ↑ 14.0 14.1 14.2 Borsani E, Della Vedova AM, Rezzani R, Rodella LF, Cristini C. Correlation between human nervous system development and acquisition of fetal skills: An overview. Brain and development. 2019 Mar 1;41(3):225-33.
  15. ↑ 15.0 15.1 15.2 15.3 15.4 15.5 15.6 15.7 Einspieler C, Prayer D, Marschik PB. Fetal movements: the origin of human behaviour. Developmental Medicine & Child Neurology. 2021 Oct;63(10):1142-8.
  16. ↑ 16.00 16.01 16.02 16.03 16.04 16.05 16.06 16.07 16.08 16.09 16.10 Fagard J, Esseily R, Jacquey L, O’regan K, Somogyi E. Fetal origin of sensorimotor behavior. Frontiers in neurorobotics. 2018 May 23;12:23.
  17. ↑ 17.0 17.1 Hadders-Algra M. Early human motor development: From variation to the ability to vary and adapt. Neuroscience & Biobehavioral Reviews. 2018 Jul 1;90:411-27.
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