Reasons for this are thought to include less one-on-one time with parents, the premature birth of twins, and the companionship of their twin sibling reducing their motivation to talk to others. A twin study has also shown that genetic factors have an important role in language delay. Monozygotic twin pairs (identical twins) recorded a higher consistency than dizygotic twin (fraternal twins) pairs, revealing monozygotic twins experiencing early vocabulary delay is attributed to genetic etiology. The environmental factors that influences both twins also play a big role in causing early language delay, but only when it is transient.Gender
Research has shown that boys are at greater risk for delayed language development than girls. Almost all developmental disorders that affect communication, speech and language skills are more common in males than in females. British scientists have found that the male sex hormone (testosterone) levels were related to the development of both autism and language disorders, which explains why boys are at a greater risk of developmental disorders biologically.Perinatal conditions
There is a high prevalence of early language delay among toddlers with neonatal brachial plexus palsy. Hand usage and gestures are part of the motor system and have been proven correlate to comprehension and production aspects in language development. An interruption in the hand/arm usage caused by this condition during stages of language development could possibly cause these children to experience language delays.Stress during pregnancy is associated with language delay. High levels of prenatal stress can result in poorer general intellectual and language outcomes.
In addition, an inability to engage in social exchanges is a sign of language delay at all ages.Communicative deficits at specific ages and milestones might indicate language delay, including:

Not smiling at 3 months
Not turning the head toward sounds at 4 months
Not laughing or responding to sounds at 6 months
Not babbling at 9 months
Not pointing and using gestures at 12 months
Not producing more than 5 words at 18 months
Not producing more than 50 words at 24 months
Losing language and/or social skills after 36 monthsLater in life, important signs include:

A lack of speech
An inability to comprehend, process, or understand language presented to the child

Consequences of Language Delay
Language delay is a risk factor for other types of developmental delay, including social, emotional, and cognitive delay. Language delay can impact behavior, reading and spelling ability, and overall IQ scores. Some children may outgrow deficits in reading and writing while others do not. Other conditions associated with language delay include attention-deficit/hyperactivity disorder, autism spectrum disorder, and social communication disorder. Causes
Language delays are the most frequent developmental delays, and can occur for many reasons. A delay can be due to being a "late bloomer", "late talker", or a more serious problem. Such delays can occur in conjunction with a lack of mirroring of facial responses, unresponsiveness or unawareness of certain noises, a lack of interest in playing with other children or toys, or no pain response to stimuli. Socio-economic factors
Socio-economic status
Children from families of low educational level are more likely to have delays and difficulties in expressive language.