Prenatal Testosterone Transfer (also known as prenatal

androgen An androgen (from Greek ''andr-'', the stem of the word meaning ) is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This includes ...

transfer or prenatal

hormone A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs or tissues by complex biological processes to regulate physio ...

transfer) refers to the phenomenon in which

testosterone Testosterone is the primary male sex hormone and androgen in Male, males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testicles and prostate, as well as promoting se ...

synthesized by a developing male

fetus A fetus or foetus (; : fetuses, foetuses, rarely feti or foeti) is the unborn offspring of a viviparous animal that develops from an embryo. Following the embryonic development, embryonic stage, the fetal stage of development takes place. Pren ...

transfers to one or more developing fetuses within the

womb The uterus (from Latin ''uterus'', : uteri or uteruses) or womb () is the organ in the reproductive system of most female mammals, including humans, that accommodates the embryonic and fetal development of one or more fertilized eggs until bi ...

and influences development. This typically results in the partial

masculinization Virilization or masculinization is the biological development of adult male characteristics in young males or females. Most of the changes of virilization are produced by androgens. Virilization is a medical term commonly used in three medical a ...

of specific aspects of female

behavior Behavior (American English) or behaviour (British English) is the range of actions of Individual, individuals, organisms, systems or Artificial intelligence, artificial entities in some environment. These systems can include other systems or or ...

cognition Cognition is the "mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...

, and

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

, though some studies have found that testosterone transfer can cause an exaggerated masculinization in males. There is strong evidence supporting the occurrence of prenatal testosterone transfer in rodents and other litter-bearing species, such as pigs. When it comes to humans, studies comparing

dizygotic Twins are two offspring produced by the same pregnancy.MedicineNet > Definition of Twin Last Editorial Review: 19 June 2000 Twins can be either ''monozygotic'' ('identical'), meaning that they develop from one zygote, which splits and forms two e ...

opposite-sex and same-sex twins suggest the phenomenon may occur, though the results of these studies are often inconsistent.

Mechanisms of transfer

Testosterone is a

steroid hormone A steroid hormone is a steroid that acts as a hormone. Steroid hormones can be grouped into two classes: corticosteroids (typically made in the adrenal cortex, hence ''cortico-'') and sex steroids (typically made in the gonads or placenta). Wit ...

; therefore it has the ability to diffuse through the

amniotic fluid The amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote. This fluid serves as a cushion for the growing fetus, but also serves to facilitate the exchange of nutrients, water, and biochemical products betwee ...

between fetuses. In addition, hormones can transfer among fetuses through the mother's bloodstream.

Consequences of testosterone transfer

During prenatal development, testosterone exposure is directly responsible for masculinizing the genitals and brain structures. This exposure leads to an increase in male-typical behavior.

Animal studies

Most animal studies are performed on rats or mice. In these studies, the amount of testosterone each individual fetus is exposed to depends on its intrauterine position (IUP). Each gestating fetus not at either end of the uterine horn is surrounded by either two males (2M), two females (0M), or one female and one male (1M). Development of the fetus varies widely according to its IUP.

Mice

In mice, prenatal testosterone transfer causes higher blood concentrations of testosterone in 2M females when compared to 1M or 0M females. This has a variety of consequences on later female behavior, physiology, and morphology. Below is a table comparing physiological, morphological, and behavioral differences of 0M and 2M female mice.

Human studies

Studies involving humans often compare opposite-sex to same-sex dizygotic twins. Females of opposite-sex twin pairs are thought to have partially masculinized traits as a result of gestating along with a male. These studies test for a range of masculinized cognitive, morphological, physiological, and behavioral traits. Studies testing for differences in behavior (i.e. temperament) tend to yield inconsistent results, while those testing perception and cognition are typically more consistent. Though supporting evidence exists, whether or not prenatal testosterone transfer occurs in humans remains debatable. Listed below are different types of opposite-sex versus same-sex twin tests used to determine whether prenatal testosterone transfer occurs in humans.

Tests of Behavior

Sensation seeking Sensation seeking is a trait theory, personality trait defined by the search for experiences and feelings, that are "varied, novel, rich and intense", and by the readiness to "take physical, social, legal, and financial risks for the sake of such ...

* Temperament * Aggression * Toy preference

Tests of Perception and Cognition

* Auditory system functioning: assessing

otoacoustic emission An otoacoustic emission (OAE) is a sound that is generated from within the inner ear. Having been predicted by Austrian astrophysicist Thomas Gold in 1948, its existence was first demonstrated experimentally by British physicist David Kemp in 19 ...

s * Expressive vocabulary * Visio-spatial cognition: assessing

mental rotation Mental rotation is the ability to rotate mental representations of two-dimensional and three-dimensional objects as it is related to the visual representation of such rotation within the human mind. There is a relationship between areas of the b ...

ability

Tests of Physiology and Morphology

* 2nd to 4th digit ratio * Tooth size *

Handedness In human biology, handedness is an individual's preferential use of one hand, known as the dominant hand, due to and causing it to be stronger, faster or more Fine motor skill, dextrous. The other hand, comparatively often the weaker, less dext ...

* Lateralization of language function: assessment on a dichotic listening test

References

{{reflist Sex hormones Embryology Testosterone