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>> LQ 4.1 What happens during the three stages of prenatal development?

We begin by looking at the process of prenatal development, describing how, over the period of 9 months, a single fertilized cell develops into a fully formed and functional newborn. We also look at how assistive reproductive technology can help couples who are dealing with infertility.

The prenatal journey begins when a follicle in a woman’s ovary matures and releases an ovum or egg during her monthly menstrual cycle in the process called ovulation. The ovum begins to travel down the fallopian tube toward the uterus. This is where fertilization occurs, when the egg is penetrated by one of the approximately 300 million sperm cells released into the woman’s reproductive system during an act of intercourse. Usually only one child is conceived at a time, but as you learned in Chapter 3, multiple births can also occur.

Ovum: An unfertilized egg.

Ovulation: The release of a mature egg from an ovary.

Although the ratio of male–to-female conceptions has been a topic of debate for a number of years, the best current evidence is that there are an equal number of male and female conceptions (Orzack et al., 2015). Although more male than female fetuses are lost in the early weeks of a pregnancy and again near the end, the overall rate of loss during the prenatal period is higher for female fetuses (Orzack et al., 2015). Consequently, by the time babies are born, the number of males exceeds the number of females. In some countries, the selective abortion of female fetuses increases the worldwide male-to-female ratio even more (United Nations Population Fund, 2017).

T/F #1

A woman is more likely to miscarry a pregnancy if she is carrying a male fetus. False

Prenatal development is divided into three stages of very different lengths. We next describe what happens in each of these stages in detail.