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Pregnancy Week by Week: Week 4

Updated on September 27, 2007

Woohoo - now you're pregnant! Finally. Find out why pregnancy isn't really pregnancy in Week One, Week Two, or even Week Three. But here we are in Week 4 and by now you may notice that telltale of all early pregnancy symptoms, no period! Instead of getting your period, you get implantation. This is technically where pregnancy begins.

What is a Due Date?

Week 4 and only just now pregnant? Your doctor figures out a due date by counting from the first day of your last menstrual period (LMP). So many women don't know when they last ovulated. Do you? You may not know the LMP either, but it's easier to pin down than ovulation. LMP is the best predictor doctor's have to determine your baby's due date.

LMP is different from gestational age, which is calculated based on the date you actually conceived. These estimates are both valuable, but keep in mind they are just that - estimates. The truth is that baby comes when baby is ready. It's relatively rare to give birth on your actual due date, and most women, especially first time mothers, will not hold their babies until well after their due dates have passed.

Conception and Implantation

Conception occurred when sperm met egg and said, let's get together. The new blastocyst (cell mass), or embryo, traveled down the fallopian tubes and into the uterus. Once there, it finds a place in the uterine lining to settle. This is implantation. Now that the embryo has made a home, cells start to specialize into those that will become the baby and those that will become the placenta.

Can you feel it? If you feel your monthly ovulation, you may feel something at implantation but most women do not. You may have cramping as well as other symptoms commonly attributed to PMS. Click here for a complete list of early pregnancy symptoms.

Fetal Development

At this point the amniotic sac and placenta start to develop. Major systems of the body like the spine and internal organs are forming. The doctor may even be able to detect a heartbeat at this point. Gender is determined by Dad! The sperm contains that chromosome that determines baby's sex. X for girl, Y for boy. There are also several ways some people believe you can tell the gender of your baby, and there are over the counter tests you can buy.

Major No-No's

There's no common consensus about just how much alcohol is harmless so American doctors and midwives generally counsel you to consume zero. It goes without saying (but I'll say it anyway) that any illegal drug use needs to end ASAP. Check with your doctor on everything else from caffeine to prescription drugs. So what if say, hypothetically, you sort of maybe tie one on and then later find out you're pregnant? Not to worry. Many a healthy baby has been born nine months after that wild birthday bash or New Year's Eve celebration. Of course, if you're planning to get pregnant or if you suspect you already are, then act accordingly.


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  • childcen profile image

    childcen 9 years ago from New Zealand

    Thanks for the valuable info.

  • profile image

    BabyGenderSelection 9 years ago

    Thank you for the useful information. I have become quite interested in baby gender selection of a baby boy or a baby girl. I found some pretty useful information so far and I am excited to share it with everyone. Also, howtoinducelabor, I use to think that was odd, too. I am working on baby # 2 and it confused me all throughout my pregnancy last time. It's because the pregnancy starts with the unfertalized egg with the potencial of it being fertilized. Very interesting indeed.

  • Barbara6 profile image

    Barbara6 10 years ago from Gainesville, FL

    i enjoyed this hub - thanks for simplifying the info that is usually presented with lots of obscure medical terms. also wonderful to see natural childbirth on your booklist!

  • profile image

    howtoinducelabor 10 years ago

    Hi again,

    Forgot to mention, thanks for this lens, it's very informative.

  • profile image

    howtoinducelabor 10 years ago

    I always thought it was so strange that when you are really only 2 weeks pregnant, it is considered 4 weeks pregnant. So the day of conception, you are considered 2 weeks pregnant. Very odd!!