"symmetric" deficiency in weight, length, all circumferences, and both fat and lean body mass
late onset defect (or intermittent, less severe defect) – usually reflects altered perfusion
"asymmetric" defect – circumference and length are normal,
ß wt for length, trunk, and limb circumference ("little old man/woman") because O2 shunted to brain at expense of other organs
low birth weight – weight < 2500 grams
macrosomic (high birth weight) – weight >4000 gms
premature – delivery before 36wks
Factors affecting fetal growth
Genetic – initially major determinant of growth, most pronounced factor
Nutrition–famine, cholesterol will provide nutrition, megavitamins can be hazardous, severe vitamin deficiencies affect fetus (esp. folate)
Perfusion
Environment – smoking, EtOH, financial standing
Placentation and placental growth – major modifier; 1st environmental restriction on embryo’s genetic growth potential
direct linear relationship between placental size/function and birth weight
placenta can regulate its own growth based on availability of substrate at the intervillous space (prevents fetus from outgrowing its substrate supply)
Positive growth factors
include maternal well being, placentation and placental growth, maternal nutrient intake, weight of mother and father at birth
most important clinical indicator is average 24 hour glucose level
Negative growth factors
include factors that ß substrate availability, placental blood flow in intervillous space
i.e. chronic environmental stress, negative color or fluid balance, hyperthermia, hypertension, deficiency in amniotic fluid (oligohydramnios), multiple gestation
Phases of Fetal Growth
Three Phases:
(1) Hyperplastic
(10-18 wks):
Ý cell number (initial tissue differentiation, organogenesis, placental development)
genetically dictated; this stage most susceptible to environmental factors (teratogens)
(2) Linear phase of growth
(18-37wks) – balanced hyperplasia and hypertrophy; linear increase in fetal mass
(3) Hypertrophic
(lasts 4-6wks) – Ý cell size, functional maturation (reduction the rate of cell division)
Growth pattern
: seen at organ, tissue, and cellular level; not asymptotic (linear growth pattern and wt. gain during 3rd trimester)
Requirements
: same as ex utero (H2O, O2, carbohydrate, protein, fat, essential amino acids, vitamins, trace minerals)
Average Growth Rates:
27 grams/day +/- 4 gms/day
Abnormal Fetal Growth
: growth rate >2 standard deviations above or below the mean (<19gm/day or >35 gm/day)
abnormal gain can be early (>33g/day, accellerating after 37th week) or late (more common, abrupt change to 40g/day)
abnormal loss can be early (<21g/day, ceasing entirely at 37th week) or late (more common, abrupt change to 10g/day)
poor fetal growth:
Ý risk for physical and neurological harm, perinatal mortality, lifetime stature effects
change in fetal growth rate from middle to late pregnancy is often indicative of maternal disease or lifestyle change