Foetal Nutrition: Key Concepts

This set of notes consolidates the material from the transcript on Nutrition during foetal life, covering concepts from conception through late gestation, and including the placenta’s role, maternal influences, macronutrient and micronutrient needs, and key research findings. The aim is to provide a comprehensive, exam-focused summary with explicit equations, study references, and practical implications.

Placenta, implantation, and early development

• Blastocyst formation occurs between 7–8 days after fertilisation. It implants into the uterine wall, and cells between the uterine wall and the blastocyst form the placenta, establishing the fetal–maternal interface essential for nutrient exchange. (Page 5)
• During the embryonic stage, organ primordia begin to form (e.g., eye, spine). In the foetal stage, organs and limbs become more developed, with the umbilical cord becoming a primary conduit for nutrients and waste exchange. (Page 6)
• The placenta comprises a fetal side and a maternal blood interface, with a thin placental wall that separates foetal blood from maternal blood to minimise direct mixing while allowing exchange. The placenta’s functions include development, nutrient exchange, and respiratory and excretory transfers (e.g., O2, CO2, urea, creatinine, uric acid). (Page 8)

Placental nutrient exchange mechanisms

• Nutrient transport occurs via several mechanisms:
  • Passive diffusion for oxygen, carbon dioxide, fats, electrolytes, and fat-soluble vitamins (driven by concentration gradients).
  • Facilitated diffusion for monosaccharides.
  • Active transport for amino acids, calcium, iron, and water-soluble vitamins (low-to-high concentration requirements).
  • Proteins generally do not cross the placenta, except immunoglobulin IgG, which provides immunity. (Page 9)

Foetal growth and body composition during gestation

• Maternal–foetal nutrient allocation drives changes in foetal body composition:
  • Water fraction drops from about 90% to ~70% by term.
  • Protein accretion remains relatively constant throughout gestation.
  • Fat accretion is low early in gestation and increases later in gestation.
  • At term, protein and fat each contribute roughly 15% of birth weight. (Page 10)
• Graphical data illustrate the progressive changes in tissue weights across gestation, with trends described in terms of weight (grams) and percentage composition over time. (Page 11)

Intrauterine Growth Restriction (IUGR) and its implications

• IUGR is characterized by foetal growth inhibition such that the foetus does not reach its genetic growth potential. Causes include maternal factors (e.g., anaemia, renal disease, heart disease, cigarette smoking, drugs, alcohol) and foetal factors (chromosomal abnormalities, infections). (Page 12)
• Maternal pre-pregnancy weight, gestational weight gain (GWG), and smoking influence birth weight. A table (Table 2.1) summarizes mean birth weight by maternal factors, emphasizing that maternal health status and behaviours impact foetal size. (Pages 13)
• Signs of IUGR include: absence of buccal fat (an “old man look”), large head with large anterior fontanelle, anxious/hyper-alert infant, poor breast bud formation, thin umbilical cord, relatively large hands/feet, loose skin folds in the neck/axilla/scapular areas, long fingernails, dry/peelable skin, small/ scaphoid abdomen, reduced skeletal muscle mass. (Page 14)
• Long-term consequences of IUGR span education and cognitive outcomes, motor development, behaviour, cerebral palsy, growth retardation, and potential higher risks of neurodevelopmental and metabolic issues later in life. (Page 15)

Maternal factors affecting foetal growth

• Maternal diet and body composition prior to and during pregnancy influence birth weight. A NZ prospective study (Watson et al., EJCN 2010) followed 504 women and found that about 5% of birth weight could be predicted by maternal dietary intake after accounting for height, weight, parity, gestational age, smoking, and baby gender. Optimal birth weight was associated with dietary energy contributions approximately as follows: ~48% from carbohydrate, ~35% from fat, and ~17% from protein. (Page 16)
• Polynomial regression analyses revealed relationships between birth weight and macronutrient energy contributions, illustrating that the optimal balance of macronutrients may influence foetal size. The following relationships were reported:
  • Carbohydrate energy percentage:
    BirthWeight ext{ (g)} = 1176 + 102 imes CarbEnergy - 1.07 imes (CarbEnergy)^2
  • Fat energy percentage:
    BirthWeight ext{ (g)} = 2297 + 70.6 imes FatEnergy - 0.97 imes (FatEnergy)^2
  • Protein energy percentage:
    BirthWeight ext{ (g)} = 2423 + 136 imes ProteinEnergy - 3.96 imes (ProteinEnergy)^2
  • Protein intake in grams:
    BirthWeight ext{ (g)} = 2926 + 12.3 imes Protein ext{(g)} - 0.053 imes igl( ext{Protein (g)}igr)^2
    (Figure 1: Polynomial regression analyses of birth weight versus different macronutrient measures.) (Pages 16–17)

Foetal macronutrient needs and metabolism

• Energy: The foetus requires energy, with practical references indicating around 650 kJ at ~25 weeks (roughly one 1 L of milk) and ~1500 kJ near 35 weeks (roughly one sandwich). Energy supply is tightly linked to maternal glucose availability and placental blood flow, with storage and triglyceride synthesis contributing to energy reserves. (Page 18)
• Glucose: Approximately 60% of foetal energy comes from glucose. The supply depends on maternal blood glucose and placental blood flow, with mechanisms for storage and triglyceride synthesis discussed. (Page 18)
• Amino acids: At ~25 weeks, lean foetal mass is about 790 g (≈15% protein). Daily amino acid supply is roughly 0.75 g/day during the first two trimesters and about 2 g/day during the third trimester. The data indicate that foetal amino acid transport exceeds the foetus’s immediate requirements, as evidenced by fetal urea production and transport dynamics. (Page 19)
• Lipids: Lipids provide energy, are essential for membranes (phospholipids), and serve as storage. Placental transfer of fatty acids occurs via lipoprotein lipase activity at the placental membrane, with free fatty acids taken up by the placenta or transferred to the foetus through carrier-mediated transport. (Page 20)
• Essential fatty acids (EFAs): Long-chain n-6 and n-3 fatty acids (arachidonic acid, EPA, DHA) are crucial for development of the brain, nervous system, and visual system. DHA is particularly abundant in the brain, which accounts for roughly one-quarter of body weight at term, and adequate EFAs are required during pregnancy. Food sources include nuts and seed oils (e.g., sunflower, olive oil); about 1 tablespoon per day is suggested. EFAs can also be mobilised from maternal adipose stores if dietary intake is insufficient. (Page 21)

Vitamins and minerals of particular importance

• Vitamin A: Essential for growth and cellular differentiation; important in early foetal development. Vitamin A content at birth is low (about 5 mg retinol per pregnancy). Low vitamin A status can affect eye development. Animal studies show that deficiencies can impair perinatal organ growth. Three rat dietary groups were used to model variegated vitamin A status: Vitamin A free (VAF), Vitamin A marginal (VAM), and Vitamin A sufficient (VAS). Deficiency affected fetal organ growth and development, with specific data on organ weights and fetal metrics. (Pages 22–24)
• Folate (folic acid): Critical for neural tube development. Spina bifida and neural tube defects (NTDs) affect about 2 per 1000 births. Adequate peri-conceptional folate provides protective effects against NTDs. Public health strategies emphasize folate supplementation in the periconceptional period. Mean dietary folate intake in some populations is ~200 μg/day. Recommended intake includes 400 μg/day for all women of childbearing potential and 5 mg/day for those at risk, starting 1 month prior to conception and continuing through the end of the first trimester. (Pages 29–33)
• Calcium: Foetal calcium accumulates mainly in the last trimester at ~330 mg/day. Maternal calcium intake contributes to foetal needs; adjustments in maternal calcium metabolism occur, but there are no long-term negative effects on maternal bone density reported. (Page 34)
• Iron: Iron accumulates during the final 8 weeks of gestation. Full-term infants typically have ~250 mg of iron at birth. Anemia causes include preterm birth. A systematic review of 44 RCTs (>43,000 women) found that daily iron supplementation reduces the risk of anemia at term and may modestly reduce the risk of low birth weight and preterm birth. (Page 35)
• Zinc: Maternal zinc deficiency can affect foetal growth and may influence neurobehavioral development in animal studies; human data on neurodevelopment are less conclusive. A randomized double-blind trial (JAMA, 1995) among zinc-deficient pregnant women showed higher birth weight and head circumference with zinc supplementation (25 mg/day) compared with placebo, along with other favorable birth outcomes. The trial reported greater mean birth weight in the zinc group (3214 g) versus placebo (3088 g), with statistical significance (p = 0.03). The table of maternal characteristics and outcomes (Table 1) provides detailed comparisons. (Pages 36–38)
• Iodine: Maternal–foetal iodine transfer is essential for normal brain development and the prevention of congenital hypothyroidism. Australia implemented mandatory fortification of non-organic bread with iodised salt from October 2009 to support adequate iodine status. (Page 39)

Alcohol, caffeine, and smoking during pregnancy

• Alcohol: Alcohol readily crosses the placenta and can interact with maternal nutrition to affect foetal growth. A common reference point suggests that approximately 2 g of alcohol per kg of maternal body weight per day could contribute to Foetal Alcohol Spectrum Disorder (FASD), with broader effects including pre- and postnatal growth deficiencies and facial/mental impairments. Abstinence during pregnancy is advised, and prior alcohol use can still influence outcomes via liver dysfunction and nutrient deficiencies that persist into pregnancy. (Pages 40–41)
• Evidence on alcohol and foetal outcomes includes assessments of small-for-gestational-age (SGA) risk at various alcohol intake levels. Some cohort data suggest increased risk with higher intake, while other studies show no clear association for moderate intake. The guidance emphasizes erring on the side of caution. (Page 43)
• Caffeine: A weak association exists between caffeine intake and miscarriage risk; rodent studies have shown teratogenic effects at high doses. Human prospective studies suggest increasing risk of foetal death with higher cup-equivalents per day, but the overall recommendation is to limit caffeine during pregnancy. Typical guidance presented includes a maximum target of around 200 mg/day, with specific conversions for beverages (e.g., coffee, tea, soda). (Pages 44–45)
• Smoking: Maternal smoking reduces foetal birth weight by roughly 150–250 g and increases the risk of low birth weight and other complications. The effect is dose-related and is linked to higher risks of stillbirth, spontaneous abortion, ectopic pregnancy, and placental complications. (Page 46)

Public health and evidence considerations

• Levels of evidence provide a framework for evaluating research strength, ranging from ecological studies (weakest) to randomized controlled trials (strongest). This hierarchy underpins recommendations and policy decisions. (Page 25)
• Vitamin A toxicity and research design: A learning activity examined how to determine adverse foetal effects from high maternal vitamin A intake. The exercise highlighted the importance of study design in inferring causality and safety thresholds. (Pages 26–27)
• Folate fortification and public health strategies: Folate supplementation and food fortification strategies aim to reduce neural tube defects. The materials discuss pros/cons of fortification and alternative strategies to increase folate intake (Page 33). Useful resources include public health websites cited in the slides. (Pages 32–33)

Study and exam preparation tips (metacognitive guidance)

• The course emphasises that everything in the material is examinable, including topics, classes, and prescribed readings. Practice with end-of-topic questions and prepare a summary table that consolidates Life Span sections: Physiological needs, Nutrient needs, Nutrient concerns, and Food strategies. (Page 47)

Summary of next topics

• The next week’s lecture covers Infancy, with no seminar scheduled (Page 48).

Practical implications and synthesis

• Maternal nutrition and lifestyle (including smoking, alcohol, caffeine, and dietary composition) have measurable effects on foetal growth and long-term outcomes. Nutrient-specific guidance (e.g., energy balance, EFAs, folate, iron, zinc, iodine) supports healthy development and reduces the risk of congenital anomalies and adverse outcomes.
• Public health strategies (folate supplementation, iodine fortification, iron supplementation, and zinc supplementation in deficient populations) are evidence-based approaches to improve birth outcomes at the population level. The presented data include both observational findings and randomized trial results, illustrating why some nutrients have strong policy support while others require more nuanced interpretation.
• The placenta acts as a dynamic organ balancing maternal and foetal needs, with nutrient transport regulated by diffusion, transporters, and placental metabolism. Understanding these mechanisms helps interpret how maternal nutrition directly influences foetal development and birth outcomes.

Key equations to remember

• Carbohydrate energy effect on birth weight:
  BirthWeight ext{ (g)} = 1176 + 102 imes CarbEnergy - 1.07 imes (CarbEnergy)^2
• Fat energy effect on birth weight:
  BirthWeight ext{ (g)} = 2297 + 70.6 imes FatEnergy - 0.97 imes (FatEnergy)^2
• Protein energy effect on birth weight:
  BirthWeight ext{ (g)} = 2423 + 136 imes ProteinEnergy - 3.96 imes (ProteinEnergy)^2
• Protein intake effect on birth weight (protein in grams):
  BirthWeight ext{ (g)} = 2926 + 12.3 imes Protein ext{(g)} - 0.053 imes ( ext{Protein(g)})^2

Quick reference by topic (concept map)

• Implantation and placenta: Blastocyst forms, implants, placenta development; placenta mediates nutrient and gas exchange with maternal–foetal barrier. (Pages 5–9)
• Foetal growth patterns: Gestational changes in water, protein, and fat; term composition. (Pages 10–11)
• Growth restriction and maternal factors: IUGR etiology, signs, long-term outcomes; maternal weight, GWG, and smoking. (Pages 12–15)
• Diet and birth weight: NZ study linking macronutrient energy distribution to birth weight; polynomial relationships illustrating optimum macronutrient balance. (Pages 16–17)
• Foetal macronutrient needs: Energy, glucose, amino acids, lipids, EFAs; AAs and lipids cross placenta via specific mechanisms; EFAs crucial for brain and vision. (Pages 18–21)
• Vitamins and minerals: Vitamin A, folate, calcium, iron, zinc, iodine; supplementation trials and population interventions; key trial data (e.g., zinc). (Pages 22–38)
• Lifestyle factors: Alcohol, caffeine, and smoking effects on foetal development; evidence and guidance. (Pages 40–46)
• Evidence framework and study design: Levels of evidence; design considerations for nutrient effects (Vitamin A example). (Pages 25–27)
• Learning and study strategies: Exam readiness and summary activities; Mentimeter prompts; next topic. (Pages 26–27, 33, 47–48)