1 Week Pregnant: Preparing Your Body for Conception

Week 1 of pregnancy is a bit of a paradox—you’re not actually pregnant yet. Pregnancy is dated from the first day of your last menstrual period (LMP), which means week 1 begins with your period. This dating system helps doctors estimate your due date and track fetal development, even though conception typically doesn’t occur until week 3.¹

Why Does Pregnancy Start Before Conception?

The medical convention of dating pregnancy from your last period might seem confusing at first. Why count weeks before you’re actually pregnant?

The answer is practical: most people know when their last period started, but pinpointing the exact moment of conception is much harder. Ovulation timing varies, and sperm can survive in the reproductive tract for up to five days.² By using a fixed reference point—the first day of your last menstrual period—healthcare providers can standardize pregnancy dating and provide consistent care.

This system means pregnancy is calculated as lasting 40 weeks or 280 days from your LMP, even though conception occurs around day 14 and the actual time from conception to birth is closer to 38 weeks or 266 days.³

What’s Happening in Your Body at Week 1?

Week 1 is your menstrual period. Your uterus is shedding the lining it built up during your previous cycle, which is why you experience bleeding.

Hormonal reset: At the start of your period, estrogen and progesterone levels drop significantly. This hormonal shift triggers menstruation and signals your body to begin preparing for a new cycle.⁴

Follicle development begins: Even as you’re menstruating, your body is already preparing for potential conception. The pituitary gland releases follicle-stimulating hormone (FSH), which stimulates several follicles in your ovaries to mature. Each follicle contains an immature egg.⁵

Endometrial shedding and renewal: The uterine lining (endometrium) that supported last cycle’s unfertilized egg is shed during your period. Simultaneously, your body begins building a fresh endometrial layer that will support a fertilized egg if conception occurs this cycle.

Preparing for Conception During Week 1

Even though you’re not pregnant yet, week 1 is an ideal time to optimize your health for conception and early pregnancy. The first few weeks after conception are critical for development, and you won’t know you’re pregnant until around week 4 or later.

Start taking prenatal vitamins: Begin a prenatal vitamin with at least 400-800 mcg of folic acid. Folic acid is essential for preventing neural tube defects, and the neural tube begins forming just 3-4 weeks after conception—often before you know you’re pregnant.⁶ The CDC recommends that all people of reproductive age who could become pregnant take folic acid daily.

Track your cycle: Use a period tracker app, basal body temperature monitoring, or ovulation predictor kits to identify your fertile window. For people with a typical 28-day cycle, ovulation usually occurs around day 14, but this varies.⁷

Eat a balanced diet: Focus on nutrient-dense whole foods including fruits, vegetables, whole grains, lean proteins, and healthy fats. Iron-rich foods (leafy greens, lean red meat, beans) and calcium sources (dairy, fortified plant milk, leafy greens) are particularly important.

Limit alcohol and caffeine: If you’re trying to conceive, consider eliminating alcohol and limiting caffeine to less than 200 mg per day (about one 12-ounce cup of coffee). Alcohol consumption can affect fertility and early fetal development.⁸

Stop smoking: Smoking reduces fertility in both women and men and increases the risk of pregnancy complications. If you smoke, talk to your healthcare provider about cessation strategies.⁹

Maintain a healthy weight: Being significantly underweight or overweight can affect ovulation and fertility. Talk to your healthcare provider about a healthy weight range for you.

Manage chronic conditions: If you have conditions like diabetes, hypertension, or thyroid disorders, work with your healthcare provider to optimize management before conception. Some medications need to be adjusted during pregnancy.

Avoid harmful substances: Stay away from recreational drugs, and check with your healthcare provider about the safety of any prescription or over-the-counter medications you’re taking.

Reduce stress: While stress alone doesn’t prevent pregnancy, chronic high stress can affect hormone balance and overall health. Practice stress-reduction techniques like yoga, meditation, or regular exercise.

Exercise regularly: Moderate physical activity supports overall health and fertility. Aim for at least 150 minutes of moderate-intensity exercise per week, unless your healthcare provider advises otherwise.¹⁰

Understanding Your Fertile Window

Since week 1 is your period, you’re not fertile yet—but it’s helpful to understand when conception is most likely to occur.

For people with a 28-day cycle, ovulation typically happens around day 14 (which corresponds to week 3 in pregnancy dating). However, cycles vary widely. Your fertile window is the five days before ovulation plus the day of ovulation itself.¹¹

Sperm can survive in the reproductive tract for up to five days, while an egg is viable for about 12-24 hours after ovulation. This means you can conceive from sex that happened several days before ovulation.¹²

Methods to track ovulation include:

• Ovulation predictor kits: These detect the surge in luteinizing hormone (LH) that occurs 24-36 hours before ovulation
• Basal body temperature tracking: Your temperature rises slightly (0.5-1°F) after ovulation
• Cervical mucus monitoring: Fertile cervical mucus is clear, stretchy, and resembles raw egg white
• Cycle tracking apps: Digital tools can help predict ovulation based on your cycle history

What to Avoid When Trying to Conceive

Excessive heat exposure: Hot tubs, saunas, and very hot baths can temporarily reduce sperm count and may not be ideal during early pregnancy.¹³

Environmental toxins: Minimize exposure to pesticides, solvents, and heavy metals when possible. Eat organic produce when feasible, especially for the “Dirty Dozen” fruits and vegetables.

Certain fish: Avoid high-mercury fish like shark, swordfish, king mackerel, and tilefish. These can accumulate in your body and affect fetal brain development.¹⁴

Raw or undercooked foods: Even before conception, practice food safety habits you’ll need during pregnancy—avoid raw seafood, undercooked eggs, and unpasteurized dairy.

When to See a Healthcare Provider

If you’re planning to conceive, consider scheduling a preconception visit with your healthcare provider. This visit can include:

• Review of your medical history and any chronic conditions
• Discussion of current medications and their safety during pregnancy
• Screening for sexually transmitted infections
• Genetic carrier screening if indicated
• Vaccination updates (rubella, varicella, flu, COVID-19)
• Discussion of lifestyle factors affecting fertility and pregnancy

If you’re under 35 and have been trying to conceive for 12 months without success, or over 35 and trying for 6 months, consult a fertility specialist.¹⁵

Tracking Your Conception Journey with Nooko

If you’re trying to conceive, Nooko can help you track your cycle, log symptoms, and prepare for pregnancy. Once you conceive, Nooko seamlessly transitions to pregnancy tracking, giving you week-by-week information about your baby’s development.

Track your period, fertile window predictions, and preconception health habits all in one place. When you get that positive pregnancy test, your data is already there, and Nooko helps you navigate every week of pregnancy with evidence-based information and personalized tips.

Download Nooko on the App Store | Get Nooko on Google Play

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References

Footnotes

1. American College of Obstetricians and Gynecologists. (2017). “Methods for Estimating the Due Date.” https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/05/methods-for-estimating-the-due-date ↩

2. Cleveland Clinic. (2023). “Conception: Fertilization, Process & When It Happens.” https://my.clevelandclinic.org/health/articles/11585-conception ↩

3. NCBI Bookshelf. (2024). “Estimated Date of Delivery.” StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK536986/ ↩

4. Mayo Clinic. (2024). “Menstrual cycle: What’s normal, what’s not.” https://www.mayoclinic.org/healthy-lifestyle/womens-health/in-depth/menstrual-cycle/art-20047186 ↩

5. Johns Hopkins Medicine. (2025). “The Menstrual Cycle.” https://www.hopkinsmedicine.org/health/wellness-and-prevention/the-menstrual-cycle ↩

6. Centers for Disease Control and Prevention. (2025). “Folic Acid Recommendations.” https://www.cdc.gov/ncbddd/folicacid/recommendations.html ↩

7. American College of Obstetricians and Gynecologists. (2025). “Evaluating Infertility.” https://www.acog.org/womens-health/faqs/evaluating-infertility ↩

8. American College of Obstetricians and Gynecologists. (2024). “Alcohol and Pregnancy.” https://www.acog.org/womens-health/faqs/alcohol-and-pregnancy ↩

9. American College of Obstetricians and Gynecologists. (2024). “Tobacco, Alcohol, Drugs, and Pregnancy.” https://www.acog.org/womens-health/faqs/tobacco-alcohol-drugs-and-pregnancy ↩

10. American College of Obstetricians and Gynecologists. (2025). “Physical Activity and Exercise During Pregnancy and the Postpartum Period.” https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2020/04/physical-activity-and-exercise-during-pregnancy-and-the-postpartum-period ↩

11. BabyCenter. (2025). “When does implantation occur?” https://www.babycenter.com/getting-pregnant/how-to-get-pregnant/when-does-implantation-occur_41001244 ↩

12. Cleveland Clinic. (2023). “Conception: Fertilization, Process & When It Happens.” ↩

13. American Society for Reproductive Medicine. (2024). “Heat and Male Fertility.” https://www.reproductivefacts.org/ ↩

14. U.S. Food and Drug Administration. (2024). “Eating Fish: What Pregnant Women and Parents Should Know.” https://www.fda.gov/food/consumers/eating-fish-what-pregnant-women-and-parents-should-know ↩

15. American College of Obstetricians and Gynecologists. (2025). “Evaluating Infertility.” ↩