Insights into early fetal development

Advanced ultrasound offers real-time 3D images, enhancing understanding of fetal development

Recent advancements in ultrasound technology have provided access to captivating real-time three-dimensional images of the fetus, allowing for greater public and clinical insight into early fetal development and movement. In this article, Dr. Julie-Claire Becher provides an overview of the latest understanding of the early stages of fetal development.

Key Points

Ultrasound provides clear images of the fetus, allowing for the study of early development and diagnosis of congenital abnormalities.
Fetal movement begins approximately 7.5 weeks after conception, and by 14 weeks, flexion, extension, rotation, thumb sucking, and yawning occur.
However, it is important to note that early movements are due to reflexes occurring at the spinal cord level, even when they appear purposeful.
Purposive movement depends on brain maturation. Reflex movements are replaced by purposeful movements starting at around 18 weeks, and disappear by about 8 months after birth. It is common for reflex activity to persist when brain damage has occurred.
The fetus is capable of hearing from around 23 weeks and responds to maternal speech. Studies have shown that fetuses can learn in response to sound.
The majority of cerebral palsy cases are caused by brain injury acquired in the womb. Abnormal neurological development before birth can be identified through ultrasound studies of fetal behavior.

The advancement of ultrasound technology has led to the creation of real-time 4D images of fetuses that are impressive to both the public and physicians. These images provide more precise identification of congenital anomalies, including facial clefts, central nervous system abnormalities, and cardiac defects. Additionally, they offer clear advantages for intrauterine procedures, such as fetal surgery. Obstetricians have found the parental reactions to pictures of their unborn baby particularly rewarding.

Motor and sensory development

The public has been surprised by images of the fetus ‘walking’ and ‘thumb-sucking’, but these movements have been well-documented in the literature for several years. For those in obstetrics and ultrasonography, the only remarkable aspect of these pictures is their definition and real-time technology. While the fetus does exhibit complex movements, the significance of these actions remains unclear.

It is not surprising to pediatricians to see images of the fetus taking steps. Newborn infants can exhibit a walking motion when held upright on a flat surface, even preterm infants can do so shortly after birth. The behaviors displayed by newborns in the early postnatal period are largely due to primitive reflex activity, which is dependent on the development of spinal reflex arcs. These reflex arcs are not under the control of the brain and are fully formed in the fetus as early as eight weeks’ gestation. Reflexes are distinct from purposeful voluntary movements that develop during the first year of life. These movements rely on the maturation of the central nervous system, specifically myelination, which begins around 18 weeks of gestation. In fact, voluntary movement cannot be mastered until all primitive reflexes have disappeared. Typically, reflex activity disappears in normal infants by around eight months of age, but it may persist in those with neurological damage.

Most of the knowledge about fetal behavior has been acquired since the introduction of ultrasonography in the 1950s. The fetus displays a wide range of behaviors, beginning with slow flexion and extension of the spine and limbs at around 7.5 weeks of gestation. The diversity of movements increases rapidly over the next 3-4 weeks, and many different movement patterns have been described, including breathing, truncal rotation, limb flexion/extension, sucking, and yawning. As the fetus approaches term, its movements become more regular and coordinated due to the maturation of the nervous system.

Fetal thumb-sucking can be observed as early as 12-14 weeks of gestation. Studies have shown that a preference for sucking a particular thumb in utero can predict head position preference in the newborn and subsequent right or left-handedness. It was previously believed that handedness was dependent on cerebral lateralization. However, research has shown that fetuses exhibit a preference for one thumb over the other as early as 12 weeks into gestation, indicating that handedness may be established before the brain has control over movement. This behavior is likely under reflex control and may eventually stimulate the brain to develop handedness and lateralization of function. This behavior is likely under reflex control and may eventually stimulate the brain to develop handedness and lateralization of function. It is important to note that this is a reflex activity and not a conscious decision made by the fetus.

Research has primarily focused on studying fetal sensory development in response to sound. It has been shown that fetuses can hear as early as 23 weeks’ gestation and respond to maternal speech with a decrease in heart rate. It has been shown that fetuses can hear as early as 23 weeks’ gestation and respond to maternal speech with a decrease in heart rate. It has been shown that fetuses can hear as early as 23 weeks’ gestation and respond to maternal speech with a decrease in heart rate. Additionally, there is evidence to suggest that fetuses can distinguish between different speech sounds and even display a preference for their mother’s native language. This prenatal experience with speech may contribute to the acquisition of language after birth.

Fetal learning and memory

Fetal learning can be observed through studies of habituation. Habituation is the decrease in a particular behavioral response that occurs when a new stimulus is repeatedly presented. In an environment of constant sensory stimulation, the ability to ignore irrelevant stimuli is essential for the efficient functioning and survival of the fetus. Although simple, habituation is one of the most widespread methods of learning, and there is strong evidence that it reflects a healthy nervous system. Studies have shown that the human fetus can habituate to sound as early as 23 weeks’ gestation. It is possible that habituation occurs even earlier in response to other sensory modalities such as taste and smell, which are functional at earlier stages of development. Fetal habituation has been found to be predictive of cognitive function in early childhood.

Additionally, researchers have investigated other aspects of fetal memory. Infants whose mothers regularly watched a popular television program during pregnancy exhibited signs of recognition, such as decreased movement and heart rate, when exposed to the program’s theme song a few days after birth. In contrast, infants whose mothers did not watch the program during pregnancy did not exhibit these behaviors. These findings suggest that fetuses are capable of learning and retaining familiar auditory stimuli during gestation.

Clinical implications

The behavior of the fetus can indicate the functioning and integrity of its nervous system. By establishing a baseline of ‘normal behavior,’ it is possible to assess the well-being of the fetus. Various deviations from normal fetal behavior have been observed in pregnancies complicated by maternal smoking or recreational drug abuse, fetal abnormalities (such as Down’s Syndrome), and in pregnancies that later resulted in spontaneous abortion.

Research has led to the conclusion that brain damage causing cerebral palsy often occurs before labor. A recent study conducted in Edinburgh found evidence of brain damage during pregnancy in most infants who had neurological symptoms and died in the newborn period. Upon review, no obvious cause could be found. Routine ultrasound imaging during pregnancy is now common practice in developed countries. The development of four-dimensional ultrasound may eventually provide detailed information about the normality of fetal behavior. Measurements of the quantity and quality of fetal movement may allow us to determine the severity and extent of any neurological damage if present. The greater the differences in behavior from a fetus with an intact nervous system, the more severe the nervous system injury. Identifying fetuses that exhibit such behavioral patterns may provide insight into the pathoaetiology of intrauterine brain injury and enable optimal management of these pregnancies.


This article was commissioned and accepted by Professor Neil McIntosh FRCP Edin, a Consultant Paediatrician in the Department of Child Life & Health at Edinburgh.


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