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Week 4
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If you've just found out you're pregnant, you might want to start by reading the previous sections.

How Big Is Your Baby?

Your developing baby is still very small. Its size varies from 0.014 inch to about 0.04 inch (0.36mm to about 1mm) in length. One millimeter is half the size of a letter ôoö on this page.

How Big Are You?

At this point, your pregnancy doesn't show at all. You haven't gained weight, and your figure hasn't changed. The illustration on page 48 gives you an idea of how small your baby still is, so you can see why you won't notice any changes yet.

How Your Baby Is Growing and Developing

Fetal development is still in the very early stages, but many great changes are taking place! The implanted blastocyst is imbedded more deeply into the lining of your uterus, and the amniotic cavity, which will be filled with amniotic fluid, is starting to form. The placenta, which plays an important role in hormone production and transport of oxygen and nutrients, is forming, and vascular networks that contain maternal blood are being established.

Germ Layers

Different layers of cells are developing. These germ layers develop into specialized parts of your baby's body, such as various organs. There are three germ layersùthe ectoderm, endoderm and mesoderm.

The ectoderm will become the nervous system (including the brain), the skin and the hair. The endoderm develops into the lining of the gastrointestinal tract, the liver, pancreas and thyroid. From the mesoderm comes the skeleton, connective tissues, blood system, urogenital system and most of the muscles.

Changes in You

You are 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!

The Corpus Luteum

When you ovulate and the egg leaves the ovary, 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 of the ruptured follicle where the egg is released and looks like a small sac of fluid on the ovary. It undergoes rapid blood-vessel development in preparation for producing hormones, such as progesterone, to support a pregnancy before the placenta takes over.

The importance of the corpus luteum is the subject of much debate. It is believed to be essential in the early weeks of pregnancy because it produces progesterone. The placenta takes over this function between 8 and 12 weeks of pregnancy. The corpus luteum lasts until about the sixth month of pregnancy, when it shrinks, although normal corpus lutea have been found with full-term pregnancies. Successful pregnancies have also occurred when the corpus luteum was removed because of a ruptured cyst as early as the 20th day after a menstrual period or about the time of implantation.

How Your Actions Affect Your Baby's Development

HIV and AIDS

Women make up one of the fastest growing groups infected with the human immunodeficiency virus (HIV). Most affected women are of childbearing age.

HIV is the causative agent of acquired immune deficiency syndrome (AIDS). The exact number of people infected with HIV is unknown. Currently it is estimated that up to 2-million people in the United States alone may be infected. The AIDS epidemic among women has grown to 15% of all reported cases.

Infection with HIV can lead to a progressive debilitation of the immune system, which is AIDS. This can leave the individual susceptible to various infections and unable to fight them.

Women at greatest risk include current or former I.V. drug users and women whose sexual partners have used drugs intravenously or engaged in bisexual activities. Women with sexually transmitted diseases, those who engage in prostitution or those who received blood transfusions before screening began are also at higher risk. If you are unsure about your risk, seek counseling about testing for the AIDS virus.

When Helen came to see me for an HIV test, she wasn't pregnant but was planning a pregnancy in the next 6 months. I told her having the HIV test before she got pregnant was a good idea. She could be reassured she was not HIV-positive when she got pregnant. I also told her it was better to have the test before she got pregnant than after. She was relieved to receive negative test results. She entered her pregnancy with greater peace of mind.

A woman infected with HIV may not have symptoms. There may be a period of weeks or months when tests do not reveal the presence of the virus. In most cases, antibodies can be detected

6 to 12 weeks after exposure. In some cases, this latent period can be as long as 18 months. Once the test is positive, a person may remain without symptoms for a variable amount of time. For every patient with AIDS, there are 20 to 30 infected individuals who have no symptoms.

There is no evidence of transmission through casual contact with water, food or environmental surfaces. There is no evidence the virus can be transmitted with RhoGAM«. (See Week 16.) A mother can pass HIV to her baby before birth or during its birth.

Pregnancy may hide some AIDS symptoms, which makes the disease harder to discover. Because the illness is a serious threat to an unborn child, counseling and psychological support are critical.

There is some positive news for women who suffer from AIDS. We know if a woman is in the early course of the illness, she can usually have an uneventful pregnancy, labor and delivery. Her baby has a 20% to 30% risk of being infected during pregnancy, birth or breastfeeding. Research has also shown that taking AZT during pregnancy decreases the risk of giving birth to a baby infected with AIDS.

There is no indication that one method of delivery (C-section versus vaginal delivery) is safer for mother or infant. Because we know it is possible for the HIV infection to spread during breastfeeding, women with HIV are advised not to breastfeed.

Testing for AIDS

Testing comprises two testsùthe ELISA test and the Western Blot test. The ELISA is a screening test. If positive, it should be confirmed by the Western Blot test. Both tests involve testing blood to measure antibodies to the virus, not the virus itself. No test should be considered positive until the Western Blot test is done. It is believed to be more than 99% sensitive and specific.

You Should also Know

Environmental Pollutants and Pregnancy

Some environmental pollutants may be harmful to a developing baby. They are particularly important for a pregnant woman to know about. Avoiding exposure to these pollutants can be very important to the well-being of a developing baby. See the list on the following page.

What Can You Do?

There is a lack of clear information on the safety or lack of safety of many chemicals in our environment. The safest course of action is to avoid exposure when possible, whether by oral ingestion or through the air you breathe. It may not be possible to eliminate all contact.

If you know you will be around various chemicals, wash your hands well before eating. Not smoking cigarettes also helps.

One reassuring fact is that most of the chemicals tested have produced illness in the mother-to-be before damage to her growing baby occurred. An environment that is healthy for you will be healthy for your developing baby.

Cocaine Use in Pregnancy

Many people use cocaine today. It can be introduced into the body by three primary routesùsniffing, smoking or injecting into a vein. When smoked, it is called crack. When it is injected directly into a vein, it is called freebasing.

Cocaine use by a pregnant woman can be very serious for the developing baby. Cocaine is a stimulant and increases the user's heart rate and blood pressure. Women who use the drug during pregnancy have a higher rate of placental abruption, the premature separation of the placenta from the uterus.

If you use cocaine during the first 12 weeks of pregnancy, you run a higher risk of miscarriage. Cocaine can also cause severe deformities in a fetus. The type of defect it causes depends on the point at which cocaine is used in the pregnancy.

Infants born to mothers who use cocaine during pregnancy have been found to have long-term mental deficiencies. Sudden infant death syndrome (SIDS) is also more common in these babies. Many babies born to women who use cocaine are stillborn.

Stop using cocaine before you stop using birth control. Damage to the embryo (later the fetus) can occur as early as 3 days after conception!

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