1 Week Pregnant: What to Expect in Your First Week of Pregnancy

ByiPrego Editorial Team

Medically reviewed by

Maureen Kelly, RN — 20+ years in L&D, postpartum, NICU, and women’s health.

Reviewed against ACOG, AAP, and Mayo Clinic guidance. Meet Maureen →

Medical Disclaimer: This article is for educational purposes only and should not replace professional medical advice. Always consult with your healthcare provider before starting any new health regimen or if you have concerns about your pregnancy. Every pregnancy is unique, and individual experiences may vary.

Welcome to week one of your pregnancy journey—though here’s something that might surprise you: you’re not actually pregnant yet. Pregnancy is dated from the first day of your last menstrual period (LMP), which means week one includes the days leading up to ovulation. Think of this as the starting line, the moment your body begins preparing for the possibility of conception. This week is all about understanding your cycle, preparing your body for the months ahead, and getting excited about what’s to come.

Understanding Week 1: The Beginning of Your Cycle

During week one of your pregnancy dating, your body is in the follicular phase of your menstrual cycle. Your period has just started (or is about to), and your pituitary gland is already sending signals to your ovaries to prepare for ovulation. Hormones like follicle-stimulating hormone (FSH) are rising, encouraging your ovaries to develop follicles—small fluid-filled sacs that each contain an egg.

While it might seem odd to talk about pregnancy when conception hasn’t occurred, this dating system makes sense from a medical standpoint. It provides consistency across pregnancies and makes it easier to estimate your due date. For more about early pregnancy, visit our first trimester guide.

Baby Development at Week 1

Size comparison: Microscopic—your future baby doesn’t exist yet.

At this stage, there’s nothing to measure in terms of your baby. Conception hasn’t occurred, so there’s no embryo or fetus. What’s happening instead is the preparation phase. Your ovaries contain millions of eggs, and this week, one is beginning its journey toward maturity. If you’re trying to conceive, learn more about how to track ovulation.

Your Body This Week

Week one brings the physical reality of menstruation:

  • Menstrual bleeding: Shedding of your uterine lining, typically lasting 3 to 7 days.
  • Cramping: Lower abdominal cramps as your uterus contracts.
  • Mood changes: Hormonal shifts may cause mood fluctuations and fatigue.
  • Bloating and tenderness: Mild bloating or breast tenderness is common.
  • Lower energy: Normal during menstruation due to hormonal shifts.

Common Symptoms at Week 1

The symptoms you experience during week one are related to menstruation, not pregnancy. However, if you’re tracking your cycle in hopes of conceiving, pay attention to your baseline:

  • Cramping: Mild to moderate is normal.
  • Headaches: Hormonal fluctuations can trigger these.
  • Food cravings or aversions: You might crave certain foods.
  • Sleep changes: Some sleep more deeply, others experience insomnia.
  • Mild temperature drop: Your basal body temperature may be slightly lower.

What to Do This Week

  • Schedule a preconception checkup to discuss your plans to conceive.
  • Start taking prenatal vitamins containing at least 400 mcg folic acid daily.
  • Begin tracking your cycle to identify your fertile window.
  • Evaluate your lifestyle: Exercise, diet, stress, and sleep habits.
  • Reduce caffeine to under 200 mg per day.
  • Eliminate harmful substances: Stop smoking and alcohol.

Nutrition Spotlight: Building Your Foundation

Your nutritional status now sets the stage for a healthy pregnancy. Focus on:

  • Folic acid: 400–800 mcg daily from leafy greens, legumes, fortified grains, and supplements.
  • Iron: Lean beef, poultry, beans, and fortified cereals.
  • Calcium: 1,000 mg daily from dairy, leafy greens, and fortified milks.
  • Omega-3 fatty acids: Fatty fish, walnuts, and flaxseeds.

For a complete guide, see our pregnancy nutrition guide and foods to avoid during pregnancy.

When to Call Your Doctor

Contact your healthcare provider if you experience:

  • Extremely heavy bleeding (soaking through more than one pad per hour)
  • Severe cramping that doesn’t respond to pain relievers
  • Periods lasting longer than seven days or occurring more frequently than every 21 days
  • Dizziness, extreme fatigue, or signs of infection

For more on warning signs, see when to call your doctor during pregnancy.

Frequently Asked Questions

Can I get pregnant during my period?

While it’s less likely, pregnancy during menstruation is possible, especially if you have a shorter cycle. Sperm can survive up to five days, so if you ovulate early, conception could occur. The most fertile window is typically five days before ovulation and the day of ovulation itself.

Should I be taking prenatal vitamins if I’m not pregnant yet?

Yes. The CDC recommends all women of childbearing age take 400 mcg of folic acid daily. Folic acid is crucial in the earliest stages of pregnancy, often before you know you’re pregnant. Learn more about the best prenatal vitamins.

How do I know when I’m ovulating?

Ovulation typically occurs around day 14 of a 28-day cycle. Signs include a rise in basal body temperature, changes in cervical mucus (clear, stretchy, egg-white-like), and mild one-sided pain. Ovulation predictor kits detect the LH surge that triggers ovulation. Check out the best fertility apps to help track.

What lifestyle changes should I make now to prepare for pregnancy?

Exercise regularly (150 minutes of moderate activity weekly), eat a balanced diet, manage stress, aim for 7–9 hours of sleep, and maintain a healthy weight. Eliminate smoking, alcohol, and recreational drugs. Reduce caffeine and ensure vaccinations are current.

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Key takeaways for the first trimester

  • Most fetal organ systems form between weeks 5 and 10. Folic acid (400–800 mcg daily) supports neural tube closure.
  • Nausea affects up to 80% of pregnancies (ACOG). It usually peaks around week 9 and resolves by week 14–16.
  • The first prenatal visit is typically scheduled between weeks 8 and 10.
  • Common symptoms — fatigue, breast tenderness, food aversions, mood swings — are driven by rising hCG and progesterone.
  • Miscarriage risk drops significantly after a heartbeat is detected on ultrasound (around week 6–8).

When to call your provider

Call your OB-GYN, midwife, or labor and delivery unit right away if you experience:

  • Heavy vaginal bleeding (more than light spotting)
  • Severe abdominal or pelvic pain
  • A severe headache that doesn’t respond to acetaminophen
  • Sudden facial, hand, or leg swelling
  • Vision changes (spots, blurring, light sensitivity)
  • Decreased fetal movement after 28 weeks (fewer than 10 movements in 2 hours during baby’s active period)
  • Signs of preterm labor: regular contractions, pelvic pressure, low back pain, fluid leaking
  • Fever over 100.4°F (38°C)

When in doubt, call. Your provider would always rather hear from you about a non-issue than miss something important.

Frequently asked questions about week 1

How big is the baby at 1 weeks pregnant?

At 1 weeks, your baby is roughly the size of a poppy seed (~0.1mm). Size estimates vary from baby to baby and are based on standardized growth charts (ACOG, NICHD).

What symptoms are common at 1 weeks pregnant?

Common first-trimester symptoms include fatigue, breast tenderness, nausea (often called morning sickness, though it can occur any time of day), food aversions, frequent urination, and mood changes. These are driven by rising hCG and progesterone.

What prenatal appointments happen around 1 weeks?

The first prenatal visit is typically scheduled between weeks 8 and 10. Expect blood work, a urine test, a discussion of medical history, and possibly a dating ultrasound.

When should I worry at 1 weeks pregnant?

Heavy bleeding (soaking a pad in an hour), severe one-sided pelvic pain (possible ectopic pregnancy), persistent vomiting that prevents fluid intake, fever over 100.4°F, or sudden cessation of all early-pregnancy symptoms warrant a same-day call to your provider.

Is what I’m feeling at 1 weeks normal?

Most of the symptoms experienced at 1 weeks are part of typical pregnancy and reflect your body’s adjustments. If anything feels alarming, severe, or unusual for you, contact your provider — trust your instincts.

Sources

  • American College of Obstetricians and Gynecologists (ACOG). Your Pregnancy and Childbirth: Month to Month (current edition). acog.org
  • American Academy of Pediatrics. Caring for Your Baby and Young Child (current edition).
  • Mayo Clinic. Pregnancy week by week. mayoclinic.org
  • National Institute of Child Health and Human Development (NICHD). Pregnancy and Pregnancy Loss research and guidance.

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