Recall: Three Periods of Prenatal Development:
Pre-embryonic = Fertilization to
Embryonic
= 2 weeks
to
Fetal
= 8 weeks
to
2 weeks
8 weeks
~38 weeks (Birth)
Typical Pregnancy: 270 – 280 days (38 – 40 weeks)
Mother: Uterus reaches to ribcage
Weight gain ~ 25 pounds
Full-term fetus
Placenta
Amniotic fluid
Enlarged uterus
Enlarged breasts
Increased blood volume
Fluid retention
Maternal storage fat
8.0 lb
1.4 lb
2.0 lb
2.0 lb
1.0 lb
4.0 lb
2.7 lb
3.5 lb
24.6 lb
(From Mitchell et al, Nutrition in Health and Disease, 16th ed.)
Pregnancy causes significant stresses on the mother:
Fetal nutrition = Significant extra load on her digestive system
- Problems regulating nutrients
- Increased risk of diabetes
Fetal wastes = Significant extra load on her kidneys
- Increased urination
- Urine more concentrated
- Increased risk of kidney failure
Joint between two pubic bones softens
- Problems standing and walking
Fetus: Surrounded by amnion and chorion.
Amniotic fluid ~ 1 liter/quart
All organs mature, but:
Lungs not inflated, but fetus inhaling amniotic fluid
No food in digestive system; fetus swallowing amniotic fluid
Temperature regulation not active
Vision restricted to light & dark
Blood shunted away from lungs
Few weeks before birth:
- Fetus rotates to head-down position
- Myometrium begins weak “Braxton Hicks” contractions
Stronger contractions prevented by progesterone
(now being produced by placenta)
Cervix is still closed, preventing fetal expulsion
Triggering Events:
- Lungs and adrenal glands of fetus
stimulate placenta to produce
chemicals called prostaglandins.
- Prostaglandins cross placenta into
mother’s blood; stimulate her pituitary
gland to secrete oxytocin.
- Prostaglandins also cause
placenta to stop producing
progesterone
Myometrium (muscle layer) of uterus begins strong, coordinated,
rhythmic contractions
Three Stages of Labor:
Effacement (thinning) and
dilation (widening) of cervix
8-24 hrs
Expulsion
15-30 min
Delivery of placenta
10-45 min
Stage 1: Effacement and dilation of cervix
Contractions begin many minutes apart, relatively weak
Gradually increase in strength and frequency
as progesterone levels from placenta decrease
Cervix thins, shortens due to pressure of fetal head – Effacement
Cervical opening widens to about 10 cm - Dilation
Amnion/chorion usually ruptures toward end of this stage
Stage 2: Expulsion of fetus
Contractions of uterus strong, regular ~ 1-2 minutes apart.
Mother may push with diaphragm and abdominal muscles.
Head enters vagina,
Stretches vagina & labia
Head turns so top of head
faces front
Head = widest part, so rest of
body follows easily
Shoulders rotate as they pass
through vagina, so baby faces
right or left
Stage 3: Delivery of placenta
Once breathing, baby no longer dependent on umbilical cord.
Can be cut.
Placenta still attached to endometrium
of uterus. Ruptured amnion and
chorion attached to placenta.
Umbilical cord extends out vagina.
Contractions of uterus continue,
loosening placenta
Placenta expelled
through vagina
Not all babies, of course, are born vaginally.
About 1/3 of all births are now Caesarean:
40 years ago: about 1/20
but
Practice dates back more than 3,000 years:
First recorded Caesarian was the birth of Chinese
Emperor Jilian ~ 1030 BCE
Usually fatal to the mother:
First well-recorded incidence of a woman
surviving a caesarean section was in
Switzerland the 1580s.
Mortality rate in 1865 >85%.
Mortality rate now ~13 per 100,000
(mortality of vaginal birth ~3.5 per 100,000)
Caesarian Birth:
Mother usually under spinal anesthesia
Awake but no sensation or movement of abdomen or lower limbs
Incisions are made though the skin, abdominal muscles, and uterus
Fetus/baby removed
Uterus, abdominal muscles, and skin sutured
In most cases, Caesarean deliveries should be done only when problems
arise during labor
- Labor is slow and hard or stops
- Fetal distress
- Problem with the placenta or umbilical cord
- Baby is too big to be delivered vaginally.
Or
When a problem is anticipated:
- Fetus not in head-down position
- Stress of labor creates additional risk to mother
- Mother has infection that could be passed to baby during vaginal birth.
- Twins or triplets (or more?)
- Scar on uterus from previous Caesarean might tear
Adjustments after Birth:
Mother:
Uterus continues to contract for days to
expel remaining functional layer of endometrium.
Uterus becomes smaller over weeks / months
Pubic joint (and other
joints) tighten over
weeks / months
Prolactin from pituitary gland continues to
stimulate production of milk in breasts
Oxytocin from pituitary gland stimulates
expression of milk from breasts
Milk: First few days = colostrum
High in fat, protein, mineral, antibodies
Later: More watery, more sugar
Adjustments after Birth:
Infant: As body cools, brain stimulates heat production.
As infant nurses, digestive system begins to produce and
secrete enzymes for digestion.
Starts breathing, lungs inflate (many minutes).
Blood starts flowing to lungs as shunts close (days).
Lots of things can go wrong during or after birth:
1) Labor & delivery begins too early or too late
2) Amnion/chorion ruptures too early or too late
3) Strong contractions can not develop
4) Fetus not head-down in uterus
5) Placenta over cervix
6) Placenta separates from uterus too early or too late
7) Fetus (or just head) too large to fit through cervix and vagina
8) Fetus (or just head) too large to fit through pelvic bones
9) Umbilical cord wrapped around fetus – gets constricted
10) Maternal hemorrhage
Past 25 years worldwide: maternal deaths during childbirth have
decreased from 532,000 annually to 303,000,
Average: ~ 216 maternal deaths per 100,000 live births.
US: ~14 per 100,000 live births.
Most dangerous country: Sierra Leone = 1,360 per 100,000 births