Week 1

Nobody tells you this, but during week 1 of pregnancy, there's no baby. There's not even a fertilized egg.

Pregnancy is dated from the first day of your last menstrual period (LMP). The clock starts about 14 days before conception actually happens. Doctors use this system because pinpointing the exact moment sperm meets egg is nearly impossible. Your LMP gives them a reliable anchor.

So what IS happening?

Your uterine lining from the previous cycle is shedding. That's your period. But behind the scenes, your body is already gearing up. Your ovaries are recruiting follicles. About 15 to 20 of them start maturing each cycle, each one holding an immature egg. Between days 5 and 7, your body selects a single dominant follicle from the pack. The rest gradually break down through a process called atresia. That one winning follicle keeps growing, fueled by rising estrogen, until it releases a mature egg at ovulation around day 14.

Your hormones are running the show. Follicle-stimulating hormone (FSH) kicks off the recruitment. As the dominant follicle takes the lead, it pumps out more estrogen, which tells your uterine lining to start rebuilding. Layer by layer, it thickens into a nutrient-rich environment ready for a fertilized egg.

The main event is still two weeks out. But every biological system involved in creating a new life is already in motion. Your hormones, your lining, your follicles. All of it moving together, like an orchestra tuning up before the concert starts.

Right now, you're on your period. Cramps, bloating, breast tenderness, mood shifts, fatigue. The usual.

But here's where this cycle gets different: if you're trying to conceive, what you put in your body this week matters more than you'd expect. The U.S. Preventive Services Task Force gives its highest recommendation (Grade A) to taking 400 to 800 micrograms of folic acid daily if you're planning or could become pregnant.

The reason is timing.

Your baby's neural tube, which becomes the brain and spinal cord, starts forming in the earliest weeks of pregnancy. That's typically before a missed period, and well before a positive test. A 2024 umbrella review combining data from multiple meta-analyses found folic acid supplementation was associated with a 77% reduction in neural tube defects. You can't go back and add folate retroactively. The window is right now.

This is also a smart week to schedule a preconception checkup if you haven't already. Your provider can review your medications (some common ones aren't safe during pregnancy), make sure vaccinations are current, and screen for conditions like thyroid disorders or diabetes. These are much easier to manage before pregnancy than during it. If you smoke or drink alcohol, your provider can help you build a plan to stop.

One more thing worth knowing: every body is different. Some people have textbook 28-day cycles and can predict ovulation down to the hour. Others run long, short, or wildly inconsistent. Both are completely normal. Neither one determines how healthy your pregnancy will be.