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Early Pregnancy:
What You Should Know
By Michele St. Martin

If you're trying to conceive, you are probably hyper-aware of the signs of early pregnancy, and you may be able to find out very early in your pregnancy that you are, indeed, pregnant.

That's what happened to Marci Hutton with her fourth pregnancy. "I found out immediately after I missed my period. We had been trying to conceive for two months (not that long, I know), and were anxious." Even before Marci confirmed her pregnancy with a home pregnancy test, she had acne, "Worse than I ever had in high school."

According to OB/GYN Dr. David Barrere, "There is no rhyme or reason why some people are afflicted with symptoms while others are not. In fact, their severity is quite variable as well. However, the most common complaints are felt to be related to hormonal stimulation."

Safeguarding the Fetus Starts Before You Know You're Pregnant
That hormonal stimulation (caused by hCG -- human Chorionic Gonadatropin) can cause symptoms from nausea to headache to breast tenderness, to name just a few. But before a newly pregnant woman even misses her period or has symptoms, the embryo inside her is developing into a fetus.

If her periods tend to be irregular; she becomes pregnant accidentally; or she's just not keeping track, it's very possible that her developing fetus could suffer unintentional harm due to the presence of teratogens (factors that interfere with normal fetal development) in the mother's body. Dr. Barrere says that common teratogens include drugs, alcohol, heat, radiation and viruses.

And early pregnancy is the time of the greatest danger to a developing fetus, according to Dr. Barrere. "The embryonic period -- 3 to 8 weeks -- is the period of greatest sensitivity. Each organ system has a peak period of sensitivity at this time." Most major birth defects occur during this time period.

Genetics can influence this: "Genetic make-up also plays a part. Some fetuses are more sensitive due to genetics, so they may show more of any effect than another fetus that was exposed at the same moment in development," says Dr. Barrere. He adds that most teratogens have the potential to cause damage only at certain times of development; while they may have a slight impact outside this window, the damage is less.

Most Sensitive Periods of Fetal Development
Note: the following dates are based on the dating used by embryologists, which means the dates are two weeks behind how an OB/GYN dates a pregnancy. While your OB/GYN may consider you four weeks pregnant at the time of your first missed period, for this article we will follow the embryologist's dating method by which the fetus would be considered two weeks old.

  • Central Nervous System: 3 to 5 weeks
  • Heart: 3 to 6 weeks
  • Ears: 4 to 8 weeks
  • Eyes: 4 to 8 weeks
  • Limbs: 4 to 8 weeks
  • Lips and palate: 5 to 8 weeks
  • Genitalia: 7 to 9 weeks
Courtesy of Dr. David Barrere

What's Happening Between Conception and the Positive Pregnancy Test
Because early pregnancy is so vital to the health of the baby you've dreamed of, it's important to understand the early development of the fetus and to be taking care of yourself as though you are already pregnant. Major organs may be developing even before you miss your period, certainly before you see the "+" sign on your home pregnancy test or start feeling tired and queasy.

Here's a timeline of what happens in early pregnancy:

  • fertilizationConception occurs when the sperm penetrates the egg. Once the egg is fertilized it is called a zygote, until it reaches the uterus about three to four days later; it is then referred to as the embryo.

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  • implantationImplantation occurs when the embryo implants in the uterus. It may float in the uterus for up to two days before implanting. Some women have very slight spotting when this occurs; this spotting is referred to as "implantation bleeding." Once the embryo implants, the placenta begins to form.

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  • implantationEmbryo Formation really gets under way at implantation. At four weeks (six weeks since last menstrual period), the embryo is about 1/5 of an inch in length. Head, mouth, liver, and intestines are beginning to take shape. Although the heart is not yet fully developed, it is beating. At 8 weeks (10 weeks since your last menstrual period), the embryo is now about one inch in length. Facial features and limbs can be detected. The nervous system and internal organs have begun to function.

It's not only interesting to be able to follow your baby's development, this knowledge can be empowering: by practicing good prenatal habits, you can get your baby off to the very best start. Not all birth defects are major: Dr. Barrere points out that while the fetus becomes increasingly desensitized to teratogens as it gets older, it is still susceptible to minor malformations and functional defects.

Expectant mom Michele Wolosyn sums it up by saying, "You can't be too careful. Women say all the time that they drank and smoke throughout their pregnancy and their baby was born fine. How about 10 years down the road? Are they still fine?"



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