Recall: Three Periods of Prenatal Development:

Pre-embryonic = Fertilization to 2 weeks Embryonic = 2 weeks to 8 weeks Fetal = 8 weeks to ~38 weeks (Birth)

Typical Pregnancy: 270 – 280 days (38 – 40 weeks)

Mother: Uterus reaches to ribcage

Weight gain ~ 25 pounds

Full-term fetus 8.0 lbPlacenta 1.4 lbAmniotic fluid 2.0 lbEnlarged uterus 2.0 lbEnlarged breasts 1.0 lbIncreased blood volume 4.0 lbFluid retention 2.7 lbMaternal storage fat 3.5 lb 24.6 lb(From Mitchell et al, Nutrition in Health and Disease, 16th ed.)

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

Pregnancy causes significant stresses on the mother:

Fetus: Surrounded by amnion and chorion. Amniotic fluid ~ 1 liter/quart

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

All organs mature, but:

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

- 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

Triggering Events:

Three Stages of Labor:

Effacement (thinning) and 8-24 hrsdilation (widening) of cervix

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 anesthesiaAwake but no sensation or movement of abdomen or lower limbs

Incisions are made though the skin, abdominal muscles, and uterusFetus/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