1. How Big Are You?
At this point, your pregnancy doesn’t show.
2. How Your Actions Affect Your Baby’s Development
During pregnancy, nearly every parent
worries about whether their baby will be perfect. Most parents worry
unnecessarily. Major birth defects occur in few births. Most birth
defects occur during the first trimester (the first 13 weeks of
pregnancy).
Structural birth defects occur when
some part of the baby’s body is not formed correctly or is missing.
Heart defects and neural-tube defects are common structural defects.
Genetic defects are caused by a mistake in a gene. Some are inherited; others occur when the egg and sperm join. Exposure to certain chemicals,
such as medicines, alcohol, drugs or toxic agents, such as radiation,
lead or mercury, account for other birth defects. Additional defects may
occur if a pregnant woman is exposed to a particular infection, such as
rubella (German measles).
By the time you miss a period, 80% of baby’s organ development has already occurred.
Teratology is the study of abnormal fetal development. A teratogen
is a substance that can cause birth defects. Those who care for
pregnant women are often asked about substances that may be harmful.
Some substances may cause major defects if
exposure occurs at a specific time in fetal development, but they may
not be harmful at other times. By the 13th week, baby has
completed major development. After that time, the effect of a substance
may be smaller growth or smaller organ size. One example is rubella. It
can cause birth defects, such as heart malformations, if the baby is
infected during the first trimester. Rubella infection later in
pregnancy is less serious.
Women’s responses to substances, and the
amount they are exposed to, vary greatly. Alcohol is a good example.
Large amounts appear to have no effect on some babies, while other
babies can be harmed by very low amounts.
Animal studies
provide much of our information, which can be helpful but cannot always
be applied to humans. Other data comes from situations in which women
were exposed who didn’t know they were pregnant or
that a particular substance could be harmful. Information gathered from
these cases is difficult to apply directly to a particular pregnancy.
The Corpus Luteum
The area on the ovary where the egg comes from is called the corpus luteum. If you become pregnant, it is called the corpus luteum of pregnancy.
The corpus luteum forms immediately after ovulation at the site where
the egg is released. It looks like a small sac of fluid. It rapidly
changes in preparation for producing hormones, such as progesterone, to
support a pregnancy before the placenta takes over.
Tip for Week 4
Second- and third-hand smoke may harm a
nonsmoking woman and her developing baby. Ask those who smoke to refrain
from smoking around you during your pregnancy and avoid places where
people smoke.
We believe the corpus luteum is important
in the early weeks of pregnancy because it produces progesterone. The
placenta takes over this function between 8 and 12 weeks of pregnancy.
Around the sixth month of pregnancy, the corpus luteum shrinks.
Pregnancy at around 4 weeks
(fetal age—2 weeks).
3. Changes in You
You’re probably expecting a period around
the end of this week. When it doesn’t occur, pregnancy may be one of the
first things you think of.
