1st Week of Pregnancy: The Journey Begins

In this article:
What's Happening with Your Body
All About Baby
Most Common Pregnancy Questions
Multiple Madness
For Your Partner
Fun Fact

Did you know that your pregnancy officially begins on the first day of your last menstrual period (LMP)? Learn what's happening in these very early stages with you and your growing baby.

Welcome to BabyZone's Pregnancy Week by Week! Each week we will provide you with information, facts, pictures, and links to other resources for the appropriate stage of your pregnancy. In the coming weeks, we'll calculate your pregnancy from your last menstrual period (LMP), and also from your gestational age, figured out by the date on which you actually conceived. Sound confusing? Read on and you'll be an expert in no time. Or go to our convenient calculator to make sure you're on track.

Remember that every pregnancy is different, and growth rates vary, so always read one week on either side of your estimated pregnancy stage. If you have any questions, please check with your healthcare provider.

What's Happening with Your Body

Note: Yes, this is the first week of your pregnancy . . . but you're not even pregnant yet! Confused? Understanding the LMP method (last menstrual period) for calculating pregnancy is tricky. Here's a primer:

Your doctor will calculate your due date by counting from the first day of your last menstrual period, or LMP. Doctors use this date because many women just don't know when they last ovulated. Try to think of it this way: Each time your body has a period, you're preparing for pregnancy, so it makes perfect sense that the first day of your menstrual cycle fits in to figuring out your baby-to-be's due date.

Pregnancy Begins Before Conception
Your pregnancy begins about two weeks before the actual conception. The first day of your last period counts toward the 40 weeks physicians use to chart your pregnancy (doctors call this the LMP, or last menstrual period). It might sound backwards at first, but every period you have is a potential pregnancy—at least that's how your body sees it.

After an egg leaves the ovary and travels through the fallopian tube, it's primed for fertilization. And your body readies itself for that possible pregnancy. During a 12- to 24-hour window as the egg is making this journey, it could be fertilized. The lining of the uterus builds up in anticipation. If the egg is unfertilized, the uterus lining will shed (this is menstruation) so that the body can prepare for the next egg—and the next potential pregnancy.

Monitoring Your Menstrual Cycle
To understand when you're primed for pregnancy, you need to know a little bit about your menstrual cycle. The average woman menstruates every 28 days, explains Dr. Timothy R.B. Johnson, MD, head of the Department of Obstetrics and Gynecology at the University of Michigan Health System. The first day of your cycle begins when you notice blood coming from your vagina. Your period lasts a few days. About 14 days after you first started menstruating, your ovaries release another egg. In other words, you're ovulating—this is a prime time to get pregnant. Over the next 14 days, or the second part of your cycle, the egg works its way to the uterus. If it goes unfertilized, the cycle begins again.

But charting this cycle is sometimes difficult. "Not all women have 28-day cycles," explains Dr. Johnson. "Some women have 30-day cycles, or even 35; other women have shorter cycles." So while your healthcare provider will give you an estimated due date based on your LMP during your first prenatal visit, only an ultrasound can give you an accurate picture of your baby's exact arrival day.

Birth Control and Pregnancy
Birth control doesn't increase your odds of infertility, although it may take you longer to get pregnant once stopping the contraceptive, advises Dr. Johnson. "It will probably take a couple of months before your cycle returns to normal." That said, Dr. Johnson knows plenty of patients who got pregnant soon after they stopped taking the pill.

If you're concerned that you've been off birth control without getting pregnant after those two months, it's important to understand that from a medical standpoint, you're not considered an infertility risk until you've gone at least one year with unprotected sex without a pregnancy.

Preparing for Pregnancy
To jumpstart a healthy pregnancy you might consider taking pretnatal vitamins, drinking orange juice for folic acid, and getting some exercise. You may not even realize when you first become pregnant so refrain from drinking alcohol, taking drugs, or smoking cigarettes when you're trying to conceive. Even prescriptions may be harmful to your developing baby, so be sure to speak to your doctor when you're ready to start a family.