Virgin and Child, Enthroned, The Master of Moulins, 1499

 

FETAL
DEVELOPMENT

 

When sperm is deposited in the vagina, it travels through the cervix and into the Fallopian tubes. Conception usually takes place in the Fallopian tube. A single sperm penetrates the mother's egg cell, and the resulting cell is called a zygote.

The zygote contains all of the genetic information (DNA) necessary to become a child. Half of the genetic information comes from the mother’s egg, and half from the father’s sperm.

The zygote spends the next few days traveling down the Fallopian tube and divides to form a ball of cells. Further cell division creates an inner group of cells with an outer shell. This stage is called a "blastocyst". The inner group of cells will become the embryo, while the outer group of cells will become the membranes that nourish and protect it.

The blastocyst reaches the uterus at roughly the fifth day, and implants into the uterine wall on about day six. At this point in the mother's menstrual cycle, the endometrium (lining of the uterus) has grown and is ready to support a fetus. The blastocyst adheres tightly to the endometrium, where it receives nourishment via the mother's bloodstream.

The cells of the embryo now multiply and begin to take on specific functions. This process is called differentiation, which produces the varied cell types that make up a human being (such as blood cells, kidney cells, and nerve cells).

There is rapid growth, and the baby's main external features begin to take form. It is during this critical period of differentiation (most of the first trimester) that the growing baby is most susceptible to damage from:

The following list describes specific changes by week.

The end of the eighth week marks the end of the "embryonic period" and the beginning of the "fetal period".


STATISTICS on VIABILITY
from Ford, The Prenatal Person, ch. 9, "Newborns"


Table 9.3: Neonatal intensive care unit, Loyola University Medical Center, survival rates, 1990—4

Gestational age, weeks

Survivors %

22—3

19 %

24—5

63 %

26—7

88 %

Source: modified from “Neonatal Survival Rates”  in Cambridge Quarterly of Healthcare Ethics 8 (1999):162.


Table 9.4: Survival rates by gestational age, 1994–6

Gestational age (weeks)

Live births

Survivors percentage

23

31

35.5 %

24

36

65.6 %

25

46

73.9 %

26

64

85.9 %

28

75

96.0 %

32

262

98.1 %

Source: modified and calculated from data in the Royal Women’s Hospital in Melbourne,  Medical Journal of Australia, June 7, 1999.