GUIDE
You are not technically pregnant yet — pregnancy is dated from the first day of your last menstrual period.
It sounds counterintuitive, but week 1 of pregnancy is your period week. Doctors use this dating system because most people know when their last period started but not exactly when ovulation or fertilization occurred. Your body is shedding last month's uterine lining and preparing to build a new one — the one that may become your baby's first home.
Be prepared from day one
At week 1, there is no baby yet — not even a fertilized egg. Your body is menstruating, shedding the uterine lining from the previous cycle. This is the very beginning of a new menstrual cycle, and your reproductive system is already preparing for what comes next. If you are actively trying to conceive, understanding this cycle is essential.
During your period, follicle-stimulating hormone (FSH) is beginning to rise, signaling your ovaries to start maturing a new batch of follicles. One of these follicles will eventually become the dominant follicle and release an egg at ovulation, typically around day 14 of a 28-day cycle. That egg, if fertilized, could become your baby.
The reason pregnancy is counted from this point — before conception even occurs — is purely practical. The first day of your last menstrual period (LMP) is a reliable, identifiable date. Ovulation timing varies, and most people do not know exactly when fertilization happens. So the medical community standardized pregnancy dating from the LMP, making a full-term pregnancy 40 weeks long even though the baby only exists for about 38 of those weeks. For a deeper look at how this works, see our guide on how to calculate your due date.
Your body is doing exactly what it does every month during menstruation. The uterine lining — the endometrium — is being shed because no fertilized egg implanted last cycle. Prostaglandins trigger uterine contractions to help expel the tissue, which is what causes period cramps.
Meanwhile, your ovaries are quietly at work. The pituitary gland is releasing FSH, which stimulates several follicles in the ovaries to begin growing. Each follicle contains an immature egg. Over the next week or so, one follicle will become dominant while the others regress. Your body is also beginning to rebuild the endometrium — laying down a fresh, blood-rich lining that will be ready to receive a fertilized egg in about two weeks.
Emotionally, you may feel the same as any other period week. If you are actively trying to conceive, you might also be feeling hopeful about the new cycle ahead. Familiarize yourself with the earliest pregnancy symptoms so you know what to watch for in the weeks ahead.
Every pregnancy is different. You may experience all, some, or none of these symptoms.
This is your preparation window. The choices you make now — nutrition, supplements, lifestyle — can meaningfully affect early fetal development even though conception has not happened yet.
If you are trying to conceive, you should already be taking 400-800 mcg of folic acid daily. Folic acid is critical for preventing neural tube defects, and the neural tube forms very early — often before you know you are pregnant. Starting now gives your body time to build adequate levels.
Knowing the length of your cycle and your typical ovulation window is one of the most useful things you can do when trying to conceive. Note the first day of your period — this is day 1 of your cycle and will become the reference point for your entire pregnancy timeline.
Some prescription and over-the-counter medications are not safe during pregnancy. If you are actively trying to conceive, talk to your provider about anything you take regularly — including supplements, herbal remedies, and NSAIDs like ibuprofen.
There is no known safe amount of alcohol during pregnancy. If you are trying to conceive, reducing or eliminating alcohol now is wise. Caffeine should be limited to under 200 mg per day (about one 12-ounce cup of coffee).
When in doubt, call your provider. No question is too small during pregnancy.
Next week, your body will finish its period and begin building up the uterine lining in preparation for ovulation. The hormonal cascade that leads to conception is already underway.
Next up: Week 2. If you are just beginning your conception journey, make sure you have a good prenatal vitamin on board. You may also want to read about early signs of pregnancy so you know what to expect once conception occurs.
This guide is for informational purposes only and is not a substitute for professional medical advice. Always consult your healthcare provider with any questions about your pregnancy.
