HR (Human Reproduction) Lecture Notes: Preparing for
Birth
Dating
● Menstrual (first day of last menstrual period)
● US (biparietal diameter) (8-14w scan)
● Gestational age (menstrual + 2w)
Estimate fetal growth
● Uterus fundus elevation
○ Increase from ~12w (palpable suprapubically) by 1cm per week
(umbilicus at 20w, episternum at 36w)
○ One of only methods in developing world
● US
○ Biparietal diameter, head circumference, crown-rump length,
femur length, abdominal diameter, estimated weight (using 3D US)
○ Doppler for UtA, UmA and MCA
Growth measurements
● Absolute BW (Birth Weight) (old)
○ Microsomia (<2500g), microsomia (>4000g)
● Relative from normal distribution of population
○ SGA (Small for Gestational Age) (<10th percentile), LGA (>90th
percentile)
● Customised growth charts including maternal weight, ethnicity, etc
(emerging)
● Ponderal index
○ Weight/length^3
○ Better than BW (correlates better with outcomes)
Growth restrictions
● Ratios of body mass/proportions are relatively independent of
maternal variables (weight, ethnicity, etc)
● Symmetric
○ Insult (e.g. genetics, infection, alcohol, drugs) appears early,
affecting all cells
○ Reducing number or size of cells
● Asymmetric growth restriction, greatest risk of poor perinatal health
○ Redistribution of circulation due to placental insufficiency
○ Spare brain, reduce e.g. liver
Factors affecting fetal growth
● Maternal factors
○ Uterine size, age
◆ Experiment: embryo from large thorough bred horse grows in
uterus of small shetland pony
, ◆ BW reduced in twins but sum is greater than two singletons
◆ Divergences in growth happens in last 10-12w (fetal weight
increases rapidly towards term as fat is laid down)
○ Environment e.g. high altitude, SES
◆ BW falls 100g per 1000m ascension
◆ Reduced effect in natives (well-adapted -> more, almost
double, UtA flow, strongly correlated with BW)
○ Nutrition, BMI
◆ Need severe insult since mother and placenta can adapt
◆ DHW
◆ Reduction in BW of mothers starved in 3rd trimester (no
maternal weight gain)
◆ Increased risk of adult disease (heart disease) for fetus of
mother starved in 1st trimester
◆ Undernutrition can raise cortisol
○ Parity
◆ BW increases for later births, especially for girls
◆ Uterus doesn’t fully revert back (e.g spiral arteries are more
easily remodelled)
○ Life-style e.g. exercise, substance abuse
○ Diseases e.g. diabetes, respiratory disorders
● Placental factors
○ Blood flow
◆ Spiral artery remodelling, complete by 10-12w (when you get
pO2 increase)
◆ Failure -> haemodynamic damage -> atherosclerotic
plaques, multiple infarcts, reduced villi and fetal capillary
SA
◆ Smoking -> constricted capillaries (reduced (or reversed)
diastolic flow in UmA), smaller IV space
○ Transporter expression e.g. due to genetics
○ Barrier function
● Fetal factors
○ Sex
◆ Boys have larger placenta -> symmetrically larger, heavier,
bigger head circumference
○ Genome
◆ Infection: ToRCH, Zika affects brain
◆ Effect usually seen in 1st trimester, symmetrical growth
restriction
○ Fetal endocrine environment
◆ Maternal hormones don’t cross placenta but can have an
indirect effect via placenta development and maternal nutrient
supply
◆ Fetal hormones, IGF-I and II from fetal liver drive growth
