Prenatal development
Ovulation and conception
• Around the midpoint of a woman’s cycle
(approximately day 14 of a 28-day cycle)
ovulation occurs
• 12-24hrs travel to uterus and wait sperm to
arrive
• Sperm can survive 3 days!
• www.cambridge.edu.au/hhd12weblinks
Prenatal development
• pregnancy is just over 9 calendar months’ or
40 weeks’ duration.
• The actual moment of conception is likely to
occur approximately 2 weeks into the 40week timeframe and the baby’s real age or
foetal age is 2 weeks behind the gestational
age.
• Pregnancy is often divided into three trimesters –
a trimester being a period that lasts for about 3
months.
The trimesters are also based on calculating
pregnancy from the first day of the mother’s last
period (40 weeks), as opposed to the stages of
pregnancy which are calculated from conception.
*Trimester one is measured from week 1–13,
*trimester two from week 14–27 and the third
*trimester from week 28–40 or birth.
• In early pregnancy there are three major
stages or periods of prenatal development.
They are determined by the timing of the key
characteristics of physical development.
• These are known as the germinal, embryonic
and foetal stages.
Germinal stage
• The first stage of prenatal development
measured from the moment of conception until
implantation (about 2 weeks post-conception).
• After this first division the fertilised egg is called
a zygote.
• four days after conception there is a group of
about 16–20 cells called a morula,
• 6 days after conception, the morula becomes a
blastocyst and attaches to the uterus known as
implantation
• Cells start to specialises and take on individual
functions this is known as differentiation
The
embryonic stage
• The second stage of prenatal development
measured from implantation (about two
weeks post conception) until the end of the
eighth week after conception.
• form three layers
• Ectoderm- brain spinal cord
• Mesoderm- heart, muscles, bones
• Endoderm-internal organs
foetal stage
• The third stage of prenatal development
measured from the end of week 8 until birth.
• time of extensive growth (in size and mass)
• Draw a timeline of prenatal development
1 Include 38 weeks along the timeline.
2 Indicate the stages of prenatal development.
3 Identify key features of development that
occur each week.