Week 1
Your baby is the size of a poppy seed
What's happening this week
Here's something that surprises almost every new parent: during week 1 of pregnancy, you're not actually pregnant yet. Pregnancy is dated from the first day of your last menstrual period (LMP), which means the clock starts about two weeks before conception even happens. So why count it? Because pinpointing the exact moment of conception is nearly impossible, and doctors need a reliable starting point. Your LMP provides that anchor.
Right now, your body is doing something remarkable — it's preparing the stage. Your uterine lining is shedding from the previous cycle and will soon begin rebuilding, creating a thick, nutrient-rich environment ready to receive a fertilized egg. Meanwhile, your ovaries are already preparing the follicles that will mature into this cycle's egg. Typically 15 to 20 eggs begin maturing in their follicles each cycle, but usually only one will become the dominant follicle and release a mature egg during ovulation.
Think of this week as the opening act. Nothing has been fertilized yet, no cells are dividing — but every biological system involved in creating a new life is warming up. Your hormones, your uterine lining, your ovaries — they're all working in concert, even though the main event is still a couple of weeks away.
Your body this week
Since week 1 is actually your menstrual period, what you're experiencing right now is familiar territory — your period. You may have cramps, bloating, breast tenderness, mood changes, and fatigue. These are all normal parts of your cycle.
But here's where this week becomes different from any other period: if you're trying to conceive, this is the perfect time to start (or continue) taking a prenatal vitamin with at least 400 micrograms of folic acid. The neural tube — which becomes your baby's brain and spinal cord — forms very early in pregnancy, often before you even know you're pregnant. Having adequate folate in your system before conception is one of the most impactful things you can do.
This is also a good week to schedule a preconception checkup if you haven't already. Your healthcare provider can review your medications, discuss any chronic conditions, and make sure you're up to date on vaccinations. If you drink alcohol or smoke, your provider may recommend stopping now — even before conception.
One thing to keep in mind: every pregnancy is different. Some people have very regular cycles and can predict ovulation with precision. Others have irregular cycles that make timing harder. Both are completely normal, and neither determines how healthy your pregnancy will be.
For dads
This might feel like the earliest possible moment to be involved, and honestly — it is. But it's also the perfect time to start. If you and your partner are trying to conceive, this week is about getting the groundwork right. That means understanding the basics of her cycle (ovulation typically happens around day 14 of a 28-day cycle, but varies widely), knowing when the fertile window opens, and being available — emotionally and practically. You might also want to look into your own health: studies show that sperm quality is affected by diet, exercise, alcohol, and stress. A checkup for you isn't a bad idea either.
This week, your partner is on her period and may be dealing with cramps, fatigue, and mood shifts. The most helpful thing you can do is small, concrete gestures — pick up her preferred comfort food, handle dinner, or just ask how she's feeling without trying to fix anything. If you're both actively trying to conceive, talk openly about expectations and timelines. The process can take longer than people expect, and having honest conversations early takes pressure off both of you.
Common concerns
Am I actually pregnant during week 1?+
No — and this confuses almost everyone. Pregnancy is dated from the first day of your last period, which is typically about two weeks before conception. Doctors use this method because the exact date of conception is rarely known. So during week 1, your body is having a normal menstrual period while preparing for a potential pregnancy.
When should I start taking prenatal vitamins?+
Ideally, you should start taking a prenatal vitamin with at least 400 micrograms of folic acid before you conceive. The neural tube forms in the first few weeks of pregnancy — often before a positive test — so having folate already in your system gives your baby the best start. Your healthcare provider can recommend a specific prenatal vitamin for you.
Does the timing of my period affect my chances of conceiving?+
Not directly, but your cycle length can affect when you ovulate. Most people ovulate about 14 days before their next period starts, not 14 days after their period begins. If your cycles are irregular, ovulation can be harder to predict. Ovulation predictor kits and tracking apps can help, but talk to your provider if you have concerns.
When should I see a doctor if I'm trying to conceive?+
A preconception checkup is a great idea for anyone planning a pregnancy. Your provider can review medications, check for any underlying conditions, and discuss lifestyle changes. If you've been trying to conceive for 12 months without success (or 6 months if you're over 35), your provider may suggest a fertility evaluation.
Product picks for week 1
We may earn a small commission if you purchase through links on this page — at no extra cost to you. Learn more.
Prenatal vitamins with folate
Start before conception — look for at least 400mcg of folic acid or methylfolate to support early neural tube development.
Basal body temperature thermometer
Track your temperature each morning to identify your ovulation pattern and pinpoint your fertile window.
Trying to conceive guidebook
An evidence-based guide covering fertility basics, timing, nutrition, and what to expect — for both partners.
A quick note: This content is for informational purposes only and is not a substitute for professional medical advice. Always talk to your healthcare provider about any questions or concerns. Learn how we create our content.
Content based on guidance from the American College of Obstetricians and Gynecologists (ACOG), the American Academy of Pediatrics (AAP), Mayo Clinic, and peer-reviewed medical literature. Learn more about how we create our content.