Week 1 of Pregnancy
Learn about your baby's development and what to expect at 1 weeks pregnant.
Baby's Size This Week
Baby Development at Week 1
- ● Week 1 of pregnancy is counted from the first day of your last menstrual period, before conception actually occurs.
- ● Your body is preparing for ovulation by developing follicles in the ovaries, each containing an immature egg.
- ● The uterine lining (endometrium) is shedding and will rebuild to prepare a nutrient-rich environment for a potential embryo.
- ● Hormones including follicle-stimulating hormone (FSH) are rising to stimulate egg maturation inside the dominant follicle.
- ● Although no embryo exists yet, this week is part of the standard 40-week pregnancy dating system used by all healthcare providers.
- ● Rising FSH signals the ovaries to begin selecting the most mature egg that will be released during ovulation around day 14.
Your Body at Week 1
- ● You are having your menstrual period, which marks the start of your pregnancy countdown.
- ● Estrogen and progesterone levels are at their lowest point, which triggers menstrual bleeding.
- ● You may experience typical period symptoms such as cramping, bloating, and fatigue.
- ● Your body is beginning to prepare for ovulation, which typically occurs around day 14 of your cycle.
- ● Mood changes are common due to hormonal fluctuations at the start of a new cycle.
- ● Prostaglandins released during menstruation may cause lower back pain and pelvic discomfort.
Week 1 Checklist
- ☐ Start taking a prenatal vitamin with at least 400 mcg of folic acid daily to protect against neural tube defects.
- ☐ Schedule a preconception appointment with your OB-GYN or midwife to review health history.
- ☐ Avoid alcohol, smoking, and limit caffeine to under 200 mg per day.
- ☐ Track your menstrual cycle using an app or calendar to identify your most fertile days.
- ☐ Review your medications with a healthcare provider to ensure they are pregnancy-safe.
- ☐ Begin eating a balanced diet rich in folate, iron, and calcium to support a healthy conception.
Frequently Asked Questions
Am I actually pregnant at week 1?
Not yet. Week 1 is counted from the first day of your last menstrual period (LMP). Conception typically occurs around week 2-3. This dating method is used because most women know their last period date but not the exact day of conception. Your actual pregnancy begins about two weeks later.
What should I start doing before getting pregnant?
Begin taking a prenatal vitamin with at least 400 mcg of folic acid to help prevent neural tube defects. Stop smoking and drinking alcohol, limit caffeine to 200 mg per day, and schedule a preconception visit with your doctor to review medications and discuss any health conditions that could affect pregnancy.
How is my due date calculated?
Your due date is typically calculated by adding 280 days (40 weeks) to the first day of your last menstrual period. This is called Naegele's rule. Your provider may adjust this date based on early ultrasound measurements. Only about 5% of babies are born on their exact due date.
When is the best time to conceive?
The most fertile window is the 5 days before ovulation and the day of ovulation itself. For most women with a 28-day cycle, ovulation occurs around day 14. Using ovulation predictor kits, tracking basal body temperature, or monitoring cervical mucus can help identify your fertile window.
Does folic acid really matter before I'm pregnant?
Yes, folic acid is critically important before conception and in the very early weeks of pregnancy. The neural tube — which develops into the brain and spinal cord — closes between weeks 3 and 4, often before a woman knows she is pregnant. Taking 400-800 mcg daily before conception reduces neural tube defects (like spina bifida) by up to 70%.
Track Your Exact Pregnancy Week
Use our free Pregnancy Week Tracker to find out exactly how far along you are based on your last menstrual period or due date.
Track My Pregnancy →Sources
- ACOG
- WHO Fetal Growth Charts
- Mayo Clinic
Medical disclaimer: This content is for informational purposes only and is not intended as medical advice. Always consult a qualified healthcare provider for guidance specific to your pregnancy.