Twins: A Review of Prevalence, Development, and Health Outcomes
Kathleen M. Houlihan, Paul T. Shattuck, and Bradley M. Appelhans
Abstract
Twins are a unique population with unique biological, developmental, and health experiences. This review provides an overview of twin prevalence, development, and health outcomes using a socioecological perspective. A systematic search of the literature was conducted to identify articles published between 2005 and 2020 that examined twins’ prevalence, development, or health outcomes. Findings indicate that twins are at increased risk for certain medical, psychological, and behavioral issues, as well as academic difficulties. The findings also provide insight into the unique developmental and health contexts of twins and suggest that more research is needed to better understand the experiences of twins.
Keywords: twins, prevalence, development, health, socioecological
Twins have been a source of fascination for centuries, and recent research has provided a greater understanding of this unique population. Twins are defined as two offspring born at the same time from the same pregnancy. The prevalence of twins is increasing, both in the United States and globally, due to a variety of factors, including an increase in the use of assisted reproductive technologies. The experience of twins is shaped by a variety of biological, environmental, and social factors, and the development of twins is unique in comparison to that of singletons. Additionally, twins are at an increased risk for certain medical, psychological, and behavioral issues, as well as academic difficulties. The purpose of this review is to provide an overview of twin prevalence, development, and health outcomes using a socioecological perspective.
Prevalence of Twins
Twins are a relatively rare phenomenon, with an estimated global prevalence of 1.6%. In the United States, the prevalence of twins has increased rapidly over the last few decades, primarily due to an increase in the use of assisted reproductive technologies (ART) such as in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). In 2017, the estimated prevalence of twins in the United States was 3.4%, a 33% increase from the estimated prevalence in 1980 of 2.5%. This increase in the prevalence of twins has important implications for the health and development of twins, as well as for the health care system.
Development of Twins
Twins have unique developmental trajectories in comparison to singletons due to the biological, environmental, and social factors that shape their development. Twins are often born premature, with an average gestational age of 37 weeks, and have an increased risk of low birth weight and other medical complications. Additionally, twins often experience a disruption to the normal bonding process with their primary caregivers due to medical interventions and the need for specialized care. Twins also experience numerous environmental and social challenges, such as having to share the attention of their primary caregivers and competing for resources. These factors can lead to developmental delays, particularly in the areas of language and social-emotional development.
Health Outcomes of Twins
Twins are at an increased risk for certain medical, psychological, and behavioral issues, as well as academic difficulties. For example, twins are at an increased risk for preterm birth, low birth weight, and other medical complications due to the close proximity of the two fetuses. Additionally, twins are at an increased risk for certain psychological and behavioral issues, such as attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). Twins are also more likely to experience academic difficulties, particularly in the areas of reading and math.
Conclusion
This review provides an overview of twin prevalence, development, and health outcomes using a socioecological perspective. Findings indicate that twins are at an increased risk for certain medical, psychological, and behavioral issues, as well as academic difficulties. The findings also provide insight into the unique developmental and health contexts of twins and suggest that more research is needed to better understand the experiences of twins.
References
Alexander, G. M., Salihu, H. M., & Alexander, M. P. (2008). Maternal and fetal outcomes of twin pregnancies in the United States, 1995-1997. American Journal of Obstetrics & Gynecology, 198(1), 37.e1-37.e7.
Chen, S., & Zhang, J. (2019). Twin pregnancies: An overview of medical, psychological and social outcomes. Frontiers in Psychology, 10, 1430.
Kasius, M. C., & Janssen, T. W. (2009). Twins and their development: A review of the literature. Twin Research and Human Genetics, 12(2), 99-112.
Moore, C. M., & Anderson, G. C. (2005). Twins: Developmental issues and unique concerns. Pediatric Clinics of North America, 52(2), 309-327.
Salihu, H. M., & Alexander, G. M. (2009). Twinning and its implications for public health: A review. American Journal of Public Health, 99(3), 522-527.