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.