Unit 4 section 5: Birth

Gestation

Period of fetal development in the uterus; lasts about 280 days

How long does a normal human pregnancy last?

About 280 days

Trimesters

How the pregnancy timeline is divided up into

Which trimester is the most critical for fetal development?

The first trimester because major organs are forming.

First Trimester

Weeks 1-12; organs begin forming and the embryo is most vulnerable to harmful substances.

During which trimester does the mother usually begin feeling the baby move?

Second trimester.

What are the three stages of birth in order?

Dilation → Expulsion → Afterbirth.

Dilation

First stage of birth in which the cervix opens.

During which stage of birth does the cervix widen?

Dilation.

Expulsion

Second stage of birth in which contractions push the baby out.

During which stage is the baby actually delivered?

Expulsion.

Afterbirth

Third stage of birth in which the placenta are expelled.

What is delivered during the afterbirth stage?

The placenta and fetal membranes.

Monozygotic Twins

1 sperm + 1 egg, zygote splits makes identical twins

Identical twins come from how many eggs and sperm?

One egg and one sperm.

Dizygotic Twins

Fraternal twins formed when two eggs are fertilized by two different sperm.

Fraternal twins come from how many eggs and sperm?

Two eggs and two sperm.

Twins are different sexes. What type of twins are they?

Dizygotic (fraternal) twins.

Conjoined Twins

Identical twins that do not completely separate during development.

What causes conjoined twins?

The embryo does not completely split.

Polar body twins

rare, they have shared maternal DNA but not paternal

what type of twin has shared maternal DNA but not paternal

polar body twins