HUMAN REPRODUCTIONBIOLOGY 269

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.)

(Mother): Fetal nutrition = Significant extra load on her 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

Milk production stimulated by prolactin from pituitary - Breasts enlarged and tender - Expression of colostrum

Joint between two pubic bones softens - Problems standing and walking

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

Lungs

No food

Temperature

Vision

Blood

All organs mature, but:

Few weeks before birth: - Fetus rotates - Myometrium begins Stronger contractions Cervix

Triggering Events:

- 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:

(thinning) and 8-24 hrs (widening) of cervix

15-30 min

10-45 min

Stage 1: Effacement and dilation of cervix

Contractions begin many minutes apart, relatively weak Gradually increase in strength and frequency

Cervix thins, shortens due to pressure of fetal head –

Cervical opening widens to about 10 cm -

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

Adjustments after Birth:

Mother:

Uterus continues to contract for days to expell remaining functional layer of endometrium.

Uterus becomes smaller over weeks / months

Pubic joint (and other joints) tighten over 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 =High in fat, protein, mineral, antibodies

Later:

Adjustments after Birth:

Infant: As body cools,.

As infant nurses,.

Starts breathing,

Blood starts flowing

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

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