Pregnancy, or gestation, is the period of time from conception to birth. On average, it comprises 40 weeks which are commonly grouped into trimesters, during which cell, embryonic, and foetal development take place.
During pregnancy, the baby's body and its organs undergo rapid development. Although some organs continue to mature after birth in order to reach full functionality, their development during gestation lays the foundation for the baby's survival outside the womb and for its healthy growth in the future.
The prerequisites for a fully functioning neurological system develop from the 3rd week of gestation onward. At the time of birth, the nervous system, the structure of the brain, and the workings of the synapses are already established.
Behavioural development starts comparably late, namely in the 3rd month of pregnancy. Important behavioral developmental milestones include breathing and swallowing motions, the grasp reflex, eye opening, response to external stimuli, foetal movement and habituation.
A developing foetus is affected by social and environmental factors such as maternal nutritional status, specific substance use (legal or illicit), and psychosocial trauma (resulting in psychological complications experienced by the parents during pregnancy). Growing evidence implicates the importance of these and other factors on the development of the foetus; manifested in epigenetic effects or gene expression modifications (Feigelman, 2011). Science shows that suboptimal or inadequate nutrient supply to the foetus lead to low birthweight or foetal malformation. Therefore, it is essential for a mother to establish good eating habits and optimise her diet as much as possible.
During pregnancy, or gestation, after the oocyte (ovum) from a female is fertilised by a sperm (spermatozoon) from a male, it undergoes several growth and developmental stages within the mother's uterus – resulting in the formation of a foetus and leading to the birth of a baby. These developmental stages include several complex processes including cellular transformations like cell division, migration, rearrangement, and differentiation or specialisation. The average term gestation is 40 weeks, or 280 days – by convention, 2 weeks are added to account for the period between the last menstruation and subsequent ovulation. Normal full-term birth occurs between gestational weeks 37-41. Pregnancies that end before 37 weeks are referred to as preterm; those after 42 weeks are defined as post-term (DiPietro, 2008).
The words growth and development have distinct definitions with regard to the pregnancy period. Growth is typically defined as an increase in cell size or number, whereas development implies the differentiation into specialised cells with distinct functions and complexities. The full foetal growth and development period is divided into two distinct phases: i) the embryonic period – until the 8th week of gestation; and ii) the foetal period – from the 9th week until the baby is born. During the embryonic period, the structures necessary to support development are created, resulting in the formation of the umbilical cord and placenta. The placenta provides the nutrients, exchanges gases and produces hormones essential to maintain a state of pregnancy (DiPietro, 2008). A foetus’s transformation usually undergoes changes in three developmental areas: somatic development, neurological development, and behavioural development (Feigelman, 2011). Some examples of the most important events for each developmental area are summarised in their respective sections. Moreover, an infographic with an overview of the key milestones of prenatal development is available here.back
By 6 days post conception, the embryo consists of a spherical mass of cells called a blastocyst. By week 3, the blastocyst has developed into a 3 germ layered structure (endoderm, ectoderm, and mesoderm), with a primary neural tube and blood vessels allowing paired heart tubes to start pumping. During week 4 to week 8, a human-like shape is formed by lateral folding of the embryo, growth at the cranial and caudal ends, and budding of arms and legs. At the end of week 8, the closing of the embryonic period, the rudiments of all major organ systems have developed. From week 9 onward, the foetal period of development begins, where somatic changes consist of rapid body growth and differentiation of tissues and organs. By the 10th week, the foetus's face is recognisably human and by week 12, the gender of external genitals becomes distinguishable. Lung development proceeds, and between weeks 20-24, the primitive alveoli have formed, which allow the lungs to be used as gas exchange organs. During the 3rd trimester, foetal weight triples and length doubles as the body starts to store protein, fat, iron and calcium (Feigelman, 2011).back
During the 3rd week, a neural plate appears at the surface of the ectodermal surface, which infolds into neural tubes and starts to differentiate into neurons, astrocytes, oligodendrocytes and ependymal cells. By week 5, the three main divisions of forebrain, midbrain and hindbrain are evident. By the end of the embryonic period (week 8), the gross structure of the central nervous system has been formed, and on a cellular level, neurons start to migrate outwards to form 6 cortical layers. Migration is complete by the 6th month, but cell differentiation still continues. By the time of birth, the structure of the brain is complete and synapses will be pruned back substantially. The baby’s experience outside the womb will result in new connections being made (Feigelman, 2011).back
Until the 3rd month, no behavioural evidence of neural function is detectable. Reflexive responses to tactile stimulation develop in a craniocaudal sequence. Breathing and swallowing motions usually appear by week 13-14, and by week 17-27 the grasp reflex appears and is fully developed. Eye opening occurs between weeks 26-28. The full range of neonatal movements can be observed by the mid-gestation stage. During the 3rd trimester, the foetus responds to external stimuli with increased heart rate and movement. Generally, foetal movement increases in response to auditory stimulation but decreases after several repetitions. This behaviour demonstrates habituation, a simple form of learning. Habituation improves in more developed foetuses, and is usually lower in neurologically impaired or physically stressed ones. Similar reactions have also been observed in response to visual and tactile stimulation (Feigelman, 2011).back
Following a healthy, balanced and varied diet is essential at every stage in life. During pregnancy, having appropriate nutritional habits – such as adequate energy, protein, vitamin and mineral intake – is essential for the wellbeing of both the mother and her developing baby. Energy requirements during the 1st trimester of pregnancy and non-pregnant woman are usually the same. In general, during pregnancy, daily caloric intake should increase approximately 300kcal. When transitioning into the 2nd resp. 3rd trimester, the daily requirement increases by an estimated 340 resp. 452kcal. However, it should be noted that this range is highly dependent on a woman’s age, body mass index and activity level (Kominiarek and Rajan, 2016).
Reliable nutrient intake is not only essential for the mother’s health during pregnancy and the healthy growth of the foetus, but is also necessary in order to achieve a positive breastfeeding or lactation period. If appropriate habits are not established, it may result in adverse birth outcomes. These include low birth weight (weight below 2500g), preterm delivery, intrauterine growth failure or disruption but also foetal and long-term effects for the developing baby (Abu-Saad and Fraser, 2010). Obesity and overweight are also associated with poor pregnancy outcomes, women in a variety of settings may be prone to gaining excessive weight during pregnancy. Obesity-associated maternal risks include gestational diabetes and preeclampsia, which puts the foetus in danger of stillbirth and congenital anomalies (Leddy et al, 2008).
According to the World Health Organization (WHO), a healthy diet should contain adequate energy, protein, and vitamins and minerals obtained through the consumption of a variety of foods – including green and orange vegetables, meat, fish, beans, nuts, whole grains, and fruit (WHO, 2016). Other key elements and recommendations are also advised during pregnancy. These include dietary interventions, such as counselling about healthy eating and keeping physically active (recommended by WHO, 2016), as well as supplementation with iron, folic acid, vitamin A, and zinc, and restriction of caffeine intake. Caffeine is one of the most widely consumed psychoactive substances in the world, but the WHO recommends caffeine restriction in context-specific cases. For pregnant women with a high daily caffeine intake (more than 300mg per day), lowering daily intake during pregnancy is recommended in order to reduce the risk of low birth weight neonates or even pregnancy loss in drastic cases (WHO, 2016).
Some of the aforementioned elements recommended for pregnant women (e.g. iron or vitamin A) are already included in food products. However, when dietary intake is not sufficient, complementary supplementation may promote a healthy and positive pregnancy (WHO, 2016). More information about important nutrients, their sources, and their effects are available in the section NaturScience.back