Human Development, Embryology, and Prenatal Nutrition: Key Concepts and Milestones

Human pattern of birth and development

Humans are secondarily altricial: babies are helpless, little motor control, sensory organs closed; large brains force early birth.

What are some adaptation that have occured to the human birth process?

Due to large brains and pelvic limits; brain growth continues after birth, requiring more nutrition and care.

Plasticity

Ability of organisms to adjust traits to their environment.

Variation

Differences due to culture and biology.

Mismatch

When biological adaptations no longer fit the current environment.

3 Components of pregnancy

Mother, infant, placenta.

Critical developmental events of the embryonic period

Fertilization, implantation, organogenesis (development of organs and systems).

Critical vs. sensitive developmental periods

Critical = must happen at that time; Sensitive = best if happens then, but possible later.

Timing of embryonic vs fetal period

Embryonic = week 3-8; Fetal = week 9 to birth.

Age at viability

22-24 weeks, depends on lungs and CNS maturity.

When does implantation occur?

Week 2, about 8-9 days after fertilization.

Germ cell layers and their outcomes

Ectoderm → nervous system, skin; Mesoderm → muscles, skeleton, kidneys, reproductive; Endoderm → lungs, digestive, liver, pancreas, bladder.

When does the neural tube close?

Week 4 (days 24-28).

When do organs begin to form?

Week 4 (heart and other major organs).

Milestones of the second trimester

Reflexes develop, brain activity detectable, sex determined.

Milestones of the third trimester

Rapid fat increase, lung surfactant develops, passive immunity from mother.

Which organ develops last?

Lungs.

Growth in 2nd vs 3rd trimester

2nd = length growth; 3rd = weight and fat gain.

Teratogen

Substance causing prenatal damage (ex: alcohol, tobacco, thalidomide, infections, mercury, lead).

Pregnancy hormones and their functions

hCG = supports progesterone, placenta; hPL = glucose for fetus; IGF = fetal growth, glucose uptake; Estrogen = placenta development; Progesterone = prevents contractions.

Fetal/placental hormones and mom's health

hPL → gestational diabetes; IGF binding proteins alter growth; fetal genes → preeclampsia risk.

Hormonal cascade during childbirth

Stage 1: contractions/dilation; Stage 2: baby delivered; Stage 3: placenta expelled.

World Bank on nutrition and development

Better nutrition → better cognitive development → more productive workforce.

Significance of the first 1000 days

Conception to age 2; critical for growth, brain, and lifelong outcomes.

Barriers to acting on 1000 days knowledge

Lack of knowledge, lack of money, lack of health resources.

Lack of knowledge

Lack of knowledge, lack of money, lack of health resources.

Effects of restricted fetal growth

Stunting, permanent cognitive/mental/physical damage, cycle of poverty.

Barker hypothesis

Theory describing postnatal effects known as Developmental Origins of Health and Disease (DOHaD).

Dutch Hunger Winter

Study showing stunted babies, higher diabetes, cognitive issues.

Guatemalan INCAP trial

Study where nutrient-rich drink improved height and cognition, strongest before age 2.

Developmental plasticity

Infant adapts to environment/resources, shaping long-term traits.

Thrifty phenotype

Poor fetal nutrition leads to permanent metabolic changes adapted to scarcity.

Barriers to nutrition education in Saksham villages

Suggested foods not part of diets; unlike Uganda where orange sweet potatoes replaced white ones.

WASH

Water, Sanitation, Hygiene — improves infant health by reducing infections.

Examples of WASH interventions

Clean water, latrines, handwashing with soap, safe food prep.

Biofortification

Increasing nutrients in crops (ex: orange sweet potatoes → more vitamin A).

Significance of first steps in Africa

Reduce burden on mothers; child becomes more independent.

Challenges to growing nutritious crops

Theft, balancing farming with childcare, labor demands.

30 million words finding

Language-rich children hear 30M more words by age 3 than poor children.

3 Ts of language stimulation

Tune in, Talk, Take turns.

Surviving vs. thriving

Surviving = reduced mortality but still malnourished; Thriving = stimulation, language, nutrition.

Altricial vs precocial development

Altricial = helpless, rapid growth, short lives; Precocial = advanced, slow growth, long lives.

Malleability of infant skull

Fontanelles allow passage through birth canal.

Painful birth and social support

Baby born backward, large head, mothers seek alloparental help.

Metabolism to brain in infants

50% of metabolism goes to brain in infants.

Definition of humans according to Hrdy

Culture, cooperation, alloparents, theory of mind, prosocial behavior.

Fetoprotective effect of morning sickness

Protects fetus by creating aversions to toxins/pathogens.

Nutrient supply to fetus mid-pregnancy

Growth of the placenta determines nutrient supply.

Pulmonary surfactants

Prevent alveoli from collapsing; key to respiratory survival.

Maternal immune system and fetus

Fetus is only 50% maternal, so proteins appear foreign.

Pregnancy effect on maternal brain structure

Increases gray matter for social info and emotion regulation.

Effects of paternal involvement

Less maternal stress, lower preterm birth, better prenatal care, better wellbeing.

Synchrony with a baby

Locked gaze and synchronized physiological responses.