The Relationship Between Finger Ratio and Development in Infants

Condition(s) studied

Investigational drug(s) / intervention(s)

Digit Ratio: The lengths of the second (2D) and fourth (4D) fingers will be measured separately on each hand. Measurements will be taken with the baby's hands placed flat on a surface with palms facing upwards. Finger length will be defined as the distance from the midpoint of the proximal crease at the base of the finger to the distal end of the finger. A digital caliper with a precision of 0.01 mm will be used, and two separate measurements will be taken for each finger, with the average value recorded. Based on these measurements, the 2D:4D finger ratio for each hand will be calculated by dividing the length of the second finger by the length of the fourth finger.

Motor development: The Peabody Developmental Motor Scale-2 (PDMS-2) is planned to be used to assess motor development. The PDMS-2 test is designed to identify developmental delays in children aged 0-72 months. It is used to evaluate children's motor development with separate tests and rating scales for both gross and fine motor skills.

Sensory processing functions: The Test of Sensory Functions in Infants was planned for use to assess babies' sensory development. The TSFI is frequently used to evaluate the sensory processing functions of infants aged 4-18 months. It is used to determine whether and to what extent a baby has a sensory processing problem. It consists of 24 items. The TSFI requires the baby to be stimulated and interact with various materials. The total score ranges from 0-49, and the test has normative values for different age groups. Although it can be used from the fourth month onwards, the most reliable and valid results are obtained between 7-18 months.

Study summary

One of the most prominent indicators of prenatal androgen exposure is considered to be the ratio of second and fourth finger lengths (2D:4D). The 2D:4D finger ratio refers to the ratio of the length of the second finger (2D; index finger) and the fourth finger (4D; ring finger). Evidence suggests that 2D:4D is developmentally stable and stabilizes from the second trimester of pregnancy. It has been reported that the 2D:4D ratio correlates positively with estrogen and negatively with testosterone. In both sexes, prenatal testosterone levels are inversely related by a 2D:4D ratio, which does not change with age. Androgens can have direct trophic effects on target cells or indirectly affect neuronal growth through neurotrophic mediators released locally by steroid-sensitive neuronal or glial cells. Prenatal testosterone can have long-term organizational effects on the structure and function of various body systems (e.g., cardiovascular and musculoskeletal systems) that are important for physical activity and exercise.

Eligibility

Primary outcome measure(s)

• Sensory processing — 12-18 months
  The Test of Sensory Functions in Infants is a standardized assessment tool designed to evaluate sensory processing abilities in infants aged 4 to 18 months. The TSFI examines responses across multiple sensory domains, including tactile, vestibular, visual, and oral-motor functions, providing a comprehensive profile of an infant's sensory processing. In the tactile deep pressure response section, it is scored as 0: reverse response, 1: mild defensive response, and 2: integrated response. In the adaptive motor response section, it is scored as 0: no response, 1: disorganized, 2: partial, 3: organized. In the visual-tactile integration section, it is scored as 0: hyperactive, 1: hyporeactive, and 2: normal. The oculomotor test section is scored as 0: no response or poorly integrated, 1: well integrated. Response to vestibular stimulation is scored as 0: adverse response, 1: mild defensive response, and 2: integrated response. The total score ranges from 0 to 49.
• Motor development — 12-18 months
  The Peabody Developmental Motor Scales, Second Edition, is a standardized tool used to assess gross and fine motor skills in children from birth to 5 years of age. The assessment comprises six subtests: reflexes, stationary, locomotion, object manipulation, grasping, and visual-motor integration, which together provide a comprehensive evaluation of a child's motor development. It has been widely validated in both typically developing children and those with various developmental disorders, making it a reliable and widely used instrument in pediatric motor assessment. Items are scored with 0, 1, and 2 points. When the child performs the item according to the specified item criteria, 2 points are given. One point is awarded when the behavior occurs, but the criteria for successful performance are not fully met. A score of 0 is given when the child is unable to try the item or does not reveal any skills when he tries it. Results are expressed as raw, standard, or total motor scores.
• Digit Ratio — 12-18 months
  The lengths of the second (2D) and fourth (4D) fingers of the participants will be measured separately on each hand. Measurements will be taken with the participants' hands placed flat on a surface with the palms facing upwards. Measurements will be performed using a digital caliper with a precision of 0.01 mm, two separate measurements will be taken for each finger, and the average value will be recorded. Based on the obtained measurements, the 2D:4D finger ratio will be calculated by dividing the 2D length by the 4D length on both hands. To increase the reliability of the measurements, the assessments will be performed twice by a researcher who is blind to motor development and sensory processing skills.

Trial sites (1)

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