Gestation and Birth

GestationGestation is the period of carrying an embryo or foetus inside the female (pregnancy).

This period lasts for approximately 36 weeks (9 months).

GestationBy the time the embryo is one month old it has the beginnings of a brain, gut, kidneys and a heart.

By two months, it is about 31 mm longs and has all the main organ systems including a beating heart.

The embryo is now called a foetus.

Foetus at 2 Months

Foetus at 2 Months

4 weeks 18 weeks 8 weeks 38

weeks

Gestation PeriodsAnimal

Average gestation

period (days)Rabbits 33Cats 62Dogs 65Lions 108Pigs 115Sheep 150Humans 259-294Cattle 283Horses 336Elephants 600-660

BirthBirth is actually a series of events.

1. During the last few weeks of pregnancy the baby usually turns upside down so its head is pressed against the cervix.

Birth2. The increased pressure on the

cervix causes the pituitary to release yet another hormone, oxytocin.

3. Higher levels of oxytocin cause the uterine walls to contract which applies more pressure to the cervix resulting in a positive feedback loop.

Positive Feedback LoopPressure

on the Cervix

Release of Oxytocin

Contractions

of the Uterus

Birth4. As more oxytocin is released the

contractions become more frequent and more intense.

5. The amnion breaks and amniotic fluid pours out (water breaking).

6. The cervix begins to dilate from the normal 5mm to about 10cm.

Birth7. When the cervix is dilated

the mother begins to push using her abdominal muscles and forces the baby out.

8. The umbilical cord is cut and soon after the placenta is passed out.