1. Introduction to prenatal development
Building a foundation for lifelong health and well-being begins very early in the process of human development. Have you considered:
- What might influence the next generation’s learning, behaviour and risk for disease during the prenatal period?
- What accounts for variations in prenatal growth and development?
- How does the environment interact with fetal genes to influence short- and long-term outcomes?
Prenatal development is a complex process that takes place in the womb – or in utero – environment. From the time of fertilization (when a sperm cell combines with an egg cell to form a zygote), to the birth of a completely unique baby about nine months later, remarkable changes occur.
The nine-month gestation period is generally divided into three-month segments called trimesters. This prenatal period is a time of extreme sensitivity in development, a matter which has become increasingly clear through scientific research. Environments internal and external to the pregnant person, including the fetal intrauterine environment, play important and interactive roles with fetal genes to influence short- and long-term outcomes. In the following video, Dr. Stephen Lye, professor in the Departments of Obstetrics & Gynaecology, Physiology and Medicine at the University of Toronto as well as executive director of the Alliance for Human Development, Lunenfeld-Tanenbaum Research Institute, explains the significance of these gene by environment interactions.
Since the developing organism has its origin in the union of the sperm with the egg, it is fundamentally important for childbearing-aged people to pay attention to their well-being even prior to conception. A completely unique set of genes, inherited from these two combining sex cells, interacts with the prenatal environment to influence how development unfolds.
In the next video, Sir Peter Gluckman, who served as the inaugural chief science advisor to the Prime Minister of New Zealand, explains the biological concept of developmental plasticity in early development. He stresses that due to the vulnerability of developing cells, tissues and organs, healthy lifestyles for all parents prior to pregnancy – as well as for gestational parents during pregnancy – promote better outcomes for offspring.
Sir Gluckman mentions how genes are turned “on” can be altered during development. In a newer area of molecular biology known as epigenetics, scientists have discovered interactions with the environment create changes in the chemical structures around genes which ultimately affect gene expression. Listen as Dr. Meaghan Jones, assistant professor in the Department of Biochemistry and Medical Genetics, University of Manitoba, describes epigenetics and explains the concept of the epigenome.
Jones reminds us that DNA in and of itself does not determine one’s destiny and that experiences are an important influence on one’s health. To review basic genetics topics such as DNA, genes, proteins, traits and heredity, explore the next link by the Genetic Science Learning Center on the University of Utah’s Learn.Genetics website. The video “Things you may not know about DNA” found under “More about DNA & Genes” reveals some interesting facts.
In the next video, Jones explains the term phenotype and reveals how our epigenome contributes to our phenotype.
Listen as Lye adds to our understanding by discussing the neutrality of gene by environment interactions. He emphasizes that the quality of environments is important since the environment interacts with genetic predispositions to influence health outcomes. (More about the role of epigenetics on long term health is explored on page 1.1 in the Developmental Origins of Health and Disease section).
Play the “Memory match” game below to review some key terms from the Learn.Genetics website and video clips featured in this section.
Prenatal growth
The developing organism within the womb depends on energy and nutrients to grow. As growth in size occurs, developing structures become more intricate in detail and sophisticated in function (World Health Organization [WHO], 2006, p. 2).
Prenatal growth is closely linked to maternal metabolism because metabolic adaptations during pregnancy regulate the availability of nutrients and energy required for fetal development. Placental hormones modify maternal physiology and glucose metabolism, increasing the supply of nutrients such as glucose to support fetal growth (Stern et al., 2021; Aye et al., 2020).
Dr. Brandy Wicklow, associate professor in the Department of Pediatrics and Child Health, University of Manitoba, clinical investigator with the Children’s Hospital Research Institute of Manitoba and pediatric endocrinologist, explains the general principles of metabolism in the next video.
Glucose, the primary fuel used by the fetus for growth and development, crosses the placenta, so glucose levels in the fetus are directly proportionate to maternal glucose levels. Carbohydrates consumed in the gestational parent’s diet are digested and converted into glucose, which enters the bloodstream through absorption in the digestive system. The fetus relies almost entirely on glucose from the maternal circulation for energy related to growth and development of the cells and organs, since fetal glucose production is minimal (Basso, 2022).
Maternal metabolism during pregnancy makes every effort to provide the fetus with the energy to grow and develop. In early pregnancy, maternal metabolism focuses on nutrient storage and enhanced insulin secretion to build energy reserves. As gestation advances, rising levels of placental hormones lead to progressive insulin resistance, which reduces maternal glucose uptake and increases circulating glucose concentrations to ensure a steady supply of fuel (glucose) for the rapidly growing fetus. These metabolic adaptations, together with adequate maternal nutrition, are critical for supporting healthy fetal growth, optimizing birth outcomes, and promoting long-term health for both the infant and the pregnant individual (Basso, 2022).
Listen as Wicklow explains insulin resistance and how this development in pregnancy supports the provision of glucose for fetal needs.
Although glucose is the first nutrient the fetus utilizes for energy, an adequate supply of amino acids, and fatty acids are fundamental for fetal growth, as these nutrients support energy, and neurodevelopmental of the fetal brain (Na et al., 2024; Guivarch et al., 2025).
Listen as Lye explains more about nutrition needs in prenatal development and early life needs after birth for healthy brain development.
Leptin, a protein hormone originally identified as a product of the obese gene, plays a central role in regulating energy balance, appetite, and body weight. During pregnancy, leptin levels substantially rise because it is produced not only by the maternal fat stores but also by the placenta, which releases it into both the maternal and fetal bloodstream. This rise in leptin helps the body adjust to the extra energy demands of pregnancy.
Early in pregnancy, leptin supports the storage of energy, while later in pregnancy it helps the body break down fat stores to provide additional fuel for the growing fetus. Leptin also plays a role in supporting the growth and function of the placenta, which is essential for delivering oxygen and nutrients to the fetus, as well as regulating how nutrients such as glucose and fats are made available to the fetus. Overall, leptin contributes to healthy fetal growth by helping ensure that enough energy and nutrients are available throughout pregnancy (Burton et al., 2017; Khan & Layden, 2017; Nuchkova et al., 2019)(Note: More information about leptin’s role in the regulation of appetite and food intake is discussed in the “Body changes and nutritional needs in pregnancy” section on page 1.2 of the module overview.)
Optimal nutrition and healthy body weight before pregnancy support early embryonic and fetal development. Rapid cell and organ development that occurs in the first trimester, and a well‑nourished state prior to conception helps ensure that nutrient stores and metabolic pathways are prepared to meet the increasing demands of pregnancy. As gestation progresses, energy demands rise substantially, and pregnant individuals typically increase their energy intake to accommodate this change. In low‑risk pregnancies without nausea or other complications, average caloric intake gradually increases, often by about 200–300 kcal per day by the second trimester to support additional maternal energy needs and fetal growth (Buccino, 2022; WHO, 2016).
Why is knowledge about healthy, balanced nutrition and healthy body weight important for people of childbearing age?
Both preconception and prenatal nutritional status influence prenatal outcomes, including birth weight and timing of birth. Adequate maternal nutrition and appropriate weight gain are associated with reduced risks of small‑for‑gestational‑age (SGA) and large‑for‑gestational‑age (LGA) birth outcomes, while poor nutritional status and excessive or inadequate weight gain are linked to adverse perinatal outcomes and long‑term health consequences for the child (Institute of Medicine & National Research Council, 2009; Black et al., 2016).
So, the offspring’s size at birth can be an indicator of earlier prenatal experiences. In 2014 across Canada (excluding Quebec), 9.1 out of 100 singleton births were considered small for gestational age and 10.2 out of 100 singleton births were considered large for gestational age (Public Health Agency of Canada, 2017b).
Public health surveillance data in Canada continue to monitor rates of SGA and LGA births as indicators of fetal health and growth patterns, with national reports documenting persistent proportions of both SGA and LGA singleton births (Public Health Agency of Canada [PHAC], 2023).
In the next video, Dr. Maggie Morris, professor, Department of Obstetrics, Gynecology and Reproductive Sciences, University of Manitoba, explains what these fetal growth terms mean and when they may indicate suboptimal development.
The following chart provides a summary of useful fetal growth terms discussed by Maggie Morris.
Prenatal development
According to Promoting Optimal Fetal Development: Report of a Technical Consultation (WHO, 2006), any one factor is less likely to cause suboptimal development than processes that involve multiple interacting factors. In terms of suboptimal development, this report further states “the most important higher level cause is deprivation in its widest sense, most particularly the failure to ensure adequate support to protect the health of a mother, before, during and after her pregnancy” (p. 17). Public health surveillance data in Canada continue to monitor rates of SGA and LGA births as indicators of fetal health and growth patterns, with national reports documenting persistent proportions of both SGA and LGA singleton births (Public Health Agency of Canada [PHAC], 2023).
Watch the next video to hear Dr. Jones concur as to how the broader context or society where individuals live can largely structure the well-being of its individuals.
Jones mentions the idea of sensitive periods to exposures in the previous video. Testing of this idea will be possible through epigenetic research. Listen as Dr. Stephen Matthews, Professor in the Departments of Physiology, Obstetrics and Gynaecology and Medicine at the University of Toronto, explains more about the sensitivity of the developing organism’s brain to its environment.
Specific processes that take place as the brain is being constructed are described in the following reading. Also explained are the time periods before and after birth during which the brain is growing in size, and developing its structure and functioning.
There are three stages of prenatal development: pre-embryonic, embryonic and fetal. Some of the known harmful influences that may occur during these stages of development are explained in the following reading.
Learn more about how fetal sex is determined and unfolds in the next reading by Dr. Emis Akbari, senior policy fellow at the Atkinson Centre, University of Toronto, and co-author of Early Childhood Education Report (2014, 2017).
As mentioned by Matthews in the preceding video, even though the developing organism will be sensitive to environmental influences throughout the entire gestation period, there are likely critical periods when the environment may have a stronger impact on various organs and systems, including the developing brain. In the fetal development readings from the previous link to the AboutKidsHealth website, the first three months of gestation were explained as a critical time for many of the developing physical structures. During this period, physical structures may be more susceptible to damage from environmental influences and thus more likely to be evident at the time of birth in the form of physical defects or malformations.
A sensitive period is a limited time span in which a part of the body or a behaviour is biologically prepared to develop rapidly. During that time, it is especially sensitive to its surroundings. If the environment is harmful, then damage occurs, and recovery is difficult and sometimes impossible” (Berk, 2014, p.85).
More in depth information about how the brain develops is explained by Dubuc on The Brain from Top to Bottom website, starting with How the Nervous System Begins immediately followed by How the Major Subdivisions of the Brain are Formed.
According to Moore and Persaud (2008), the first major system to start working in the embryo is the cardiovascular system. The primitive heart and vascular system develop to the point where initial heart beats begin a mere 22-23 days following conception. The increase in demand for oxygen and nutrients from rapid embryonic growth drives the occurrence of these new circulatory developments (Moore & Persaud, 2008, p. 191).
The following two-page activity on the Cove Point Foundation Congenital Heart Resource Center website illustrates how fetal circulation functions. The second page highlights the remarkable changes that occur at birth within the fetal circulatory system as the newborn transitions to its new environment.
Listen as Wicklow describes the metabolic adjustments newborns need to make to extrauterine life and the significance of having an adequate store of fetal fuels for energy during these transitions.
Play the “Fetal Fact Finder” game below to review information from the AboutKidsHealth website about fetal development through each month of pregnancy.
Birth
Optimal fetal development can be defined as that state at birth in which the neonate is most likely to survive and thrive through the neonatal transition and infancy, and to be prepared such that early developmental effects do not impact negatively on the individual’s life-course” (WHO, 2006, p. 14).
Birth is experienced as a momentous occasion by many parents. If birth occurs between 37– 42 weeks of gestation, it is considered full term, and has less fetal risk associated with the timing of the birth. Prior to 37 weeks, birth is considered premature. If birth occurs after 42 weeks of gestation, it is considered postmature or postterm.
Labor usually begins when a pregnant individual starts having regular, painful contractions that gradually open (dilate) the cervix. These contractions tend to come at steady intervals and become closer together, longer, and stronger over time. As this happens, the cervix softens, thins, and opens to prepare for birth. Rather than starting all at once, labor often develops over a few days. During this time, the body is going through many changes involving the uterus, cervix, and surrounding tissues. Exactly what triggers labor isn’t fully understood, but it’s influenced by a mix of factors, such as the pregnant individual’s health, hormone levels, genetics, placenta functioning, and signals from the baby. Other influences can also play a role, such as stress, environment, and medical care. Increasingly, researchers recognize that broader social and structural factors included in the social determinates of health, like access to care and ongoing life stress, can affect when labor begins. For example, differences in stress levels and life circumstances are thought to contribute to higher rates of early (preterm) birth in some populations (King & Zengion, 2024, p.1029).
During childbirth, the stress of contractions triggers the fetus’s production of stress hormones, such as cortisol, which are beneficial at this stage to assist the fetus in coping with oxygen deprivation by directing blood to vital organs, preparing the lungs for breathing by clearing fluid and expanding the airway, and promoting alertness after birth. Unlike prenatal stress, which can be harmful, this stress response is adaptive and supports the fetus’s successful transition to life outside the womb (Berk, 2022, p. 76).
Dr. Matthews mentions in a previous video clip how sensitive the brain is to its environment. What could this mean for a premature baby who is developing the remaining weeks of gestation outside of the womb environment?
Are you aware of some other challenges faced by premature babies?
What do you know about your own birth?
How different might your birth have been if you lived in another part of the world?
Click the link below to the AboutKidsHealth website to read about the vulnerabilities of babies born prematurely.
Outcomes for birthing parents and their infants are also influenced by the quality of care received during labour and delivery. Risks such as infection and bleeding in the birthing parent, or a lack of oxygen within the fetus (which could be injurious to its brain and other organs) can be significantly reduced through the provision of needed care, based on an accurate assessment and analysis of treatment priorities (WHO, 2006, p. 6).
Play through the interactive activity below by Chaddha (2008) on the Public Broadcasting Service NOVA website to discover what happens during each of the three stages of childbirth (prior to a stage of recovery). Some of the possible risks and treatments during each stage are outlined from a global perspective.
The webpage Normal Childbirth on The Society of Obstetricians and Gynaecologists of Canada website outlines the differences between natural, normal and assisted childbirth. As you read, consider how the availability of a trained caregiver with appropriate resources could be a significant factor in prenatal outcomes.
On the following link to the WHO website, there is an update on the progress made towards Millennium Development Goals. In particular, see Millennium Development Goal #5: Improve Maternal Health.
The third of 17 Sustainable Development Goals outlined in the United Nations (2015) document Transforming Our World: The 2030 Agenda for Sustainable Development is to “ensure healthy lives and promote well-being for all at all ages” (p.18). The new targets related to this goal build upon earlier progress made towards the Millennium Development Goals. Across all countries, the first two of the new targets for the third goal are:
3.1. By 2030, reduce the global maternal mortality ratio to less than 70 per 100,000 live births
3.2 By 2030, end preventable deaths of newborns and children under 5 years of age, with all countries aiming to reduce neonatal mortality to at least as low as 12 per 1,000 live births and under-5 mortality to at least as low as 25 per 1,000 live births (United Nations, 2015, p. 18).
“Small size at birth—due to preterm birth or small-for-gestational-age (SGA), or both—is the biggest risk factor for more than 80% of neonatal deaths and increases risk of post-neonatal mortality, growth failure, and adult-onset non-communicable diseases” (Lawn et al., 2014, p. 189).
Listen as Dr. Zulfiqar Bhutta, founding director at the Centre of Excellence in Women and Child Health, Aga Khan University and Inaugural Robert Harding Chair in Global Child Health at the Hospital for Sick Children, Toronto, talks about a potential complication called birth asphyxia as it applies in particular to the context of developing countries like Pakistan.
Read more about possible causes, symptoms and treatments for birth asphyxia on the Seattle Children’s Hospital website.
